Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices — United States, 2023–24 Influenza Season

Trends in the administration of COVID-19 vaccines with other vaccines in the United States reported to V-safe during December 14, 2020-May 19, 2023

Introduction COVID-19 vaccines may be administered with other vaccines during the same healthcare visit. COVID-19 monovalent (Fall 2021) and bivalent (Fall 2022) vaccine recommendations coincided with annual seasonal influenza vaccination. Data describing the frequency of the co-administration of COVID-19 vaccines with other vaccines are limited. Methods We used V-safe, a voluntary smartphone-based U.S. safety surveillance system established by the CDC, to describe trends in the administration of COVID-19 vaccines with other vaccines reported to V-safe during December 14, 2020 - May 19, 2023. Results Of the 21 million COVID-19 vaccinations reported to V-safe, 2.2% (459,817) were administered with at least 1 other vaccine. Co-administration most frequently occurred during the first week of October 2023 (27,092; 44.1%). Most reports of co-administration included influenza vaccine (393,003; 85.5%). Co-administration was most frequently reported for registrants aged 6 months-6 years (4,872; 4.4%). Conclusion Reports of co-administration to V-safe peaked during October 2023, when influenza vaccination most often occurs, possibly reflecting increased opportunities for multiple vaccinations and greater acceptability of the co-administration of COVID-19 vaccine with other vaccines, especially influenza vaccine.

Antibody response to sequential vaccination with cell culture, recombinant, or egg-based influenza vaccines among U.S. adults

The immune response to inactivated influenza vaccines (IIV) is influenced by multiple factors, including hemagglutinin content and egg-based manufacturing. Only two US-licensed vaccines are manufactured without egg passage: cell culture-based inactivated vaccine (ccIIV) and recombinant vaccine (RIV). We conducted a randomized open-label trial in central Wisconsin during the 2018-19 and 2019-20 seasons to compare immunogenicity of sequential vaccination. Participants 18-64 years old were randomized 1:1:1 to receive RIV, ccIIV or IIV in strata defined by number of influenza vaccine doses in the prior 3 years. They were revaccinated with the same product in year two. Paired serum samples were tested by hemagglutination inhibition against egg-adapted and cell-grown vaccine viruses. Serologic endpoints included geometric mean titer (GMT), mean fold rise, and percent seroconversion. There were 373 participants randomized and vaccinated in 2018-19; 332 were revaccinated in 2019-20. In 2018-19, RIV and ccIIV were not more immunogenic than IIV against A/H1N1. The post-vaccination GMT against the cell-grown 3C.2a A/H3N2 vaccine virus was higher for RIV vs IIV (p = .001) and RIV vs ccIIV (p = .001). The antibody response to influenza B viruses was similar across study arms. In 2019-20, GMT against the cell-grown 3C.3a A/H3N2 vaccine virus was higher for RIV vs IIV (p = .03) and for RIV vs ccIIV (p = .001). RIV revaccination generated significantly greater backboosting to the antigenically distinct 3C.2a A/H3N2 virus (2018-19 vaccine strain) compared to ccIIV or IIV. This study adds to the evidence that RIV elicits a superior immunologic response against A/H3N2 viruses compared to other licensed influenza vaccine products.

Bibliometric and visual analyses of vaccine literacy research from 1982 to 2023

Vaccine literacy (VL) is an important part of health literacy (HL), which is of great significance in reducing vaccine hesitancy and improving vaccine coverage rate. We aimed to perform a bibliometric analysis of VL research conducted from 1982 to 2023 to evaluate its current status and prospects. All relevant publications were retrieved from the Web of Science Core Collection database and the Scopus database. The Bibliometrix R-package and VOSviewer software were used to analyze the publication outputs, countries, organizations, authors, journals, cited publications, and keywords. In total, 1,612 publications were included. The number of articles published on VL generally showed an increasing trend. The United States was in a leading position among all countries and had the closest connections with other countries and organizations. Its in-depth study of vaccine hesitancy provided a good foundation for VL research. Harvard University was the most productive organization. Bonaccorsi G was the most productive and cited author. VACCINES was the most productive journal. Research topics primarily revolved around vaccination, HL, vaccine hesitancy, and COVID-19 vaccine. In conclusion, the current research on the conceptual connotation and influencing factors of VL is insufficiently deep and should be further improved in the future to distinguish it from HL in a deeper manner. More tools for measuring VL need to be developed, such as those applicable to different populations and vaccines. The more complex relationship between VL, vaccine hesitancy and vaccination needs to be further explored. Gender differences deserve further investigation.

Education for Healthcare Providers: Impact of Academic Detailing on Reducing Misinformation and Strengthening Influenza Vaccine Recommendations

BACKGROUND

Recommendations from a trusted healthcare provider have been shown to be the most effective intervention for encouraging patients to be vaccinated. However, providers have reported feeling less prepared to address vaccination questions and having less time to discuss vaccines with patients than before the COVID-19 pandemic. Providers may benefit from a brief update about the available influenza vaccines and vaccination guidelines. Academic detailing is an evidence-based approach for preparing healthcare providers to discuss getting vaccinated with patients.

METHODS

An academic detailing presentation was developed using influenza statistics, vaccination recommendations, and recent local and national immunization rate data. Academic detailing was conducted with physicians and community pharmacy personnel in Yakima County, Washington, between November 2023 and January 2024. Yakima County is designated as a medically underserved area due to a lack of providers. A pre-detailing survey was conducted to evaluate participant knowledge of current ACIP recommendations and gather opinions about local resident vaccination barriers. A post-detailing survey was conducted to gather participants' opinions about the value of detailing.

RESULTS

Prior to the training, 73% of providers believed it was important to discuss influenza vaccination with patients, but only 52% felt confident in combating misinformation. Healthcare providers believed misinformation and vaccine hesitancy are the most common barriers for Yakima County patients, but recent survey results showed that online scheduling systems, long wait times, and limited appointment hours were the predominant issues reported locally. Two out of 12 community pharmacy personnel and zero resident physicians correctly named all three preferentially recommended influenza vaccines for patients 65 years and older. Overall, 96% of detailing participants reported that the session was valuable, 87% believed it would help them combat vaccine misinformation, and 65% reported planning to have more conversations with patients about influenza vaccination after participating.

CONCLUSION

Physicians and community pharmacy immunizers found the influenza vaccines academic detailing to be valuable. Staying up to date on vaccination guidelines can prepare providers to be confident in having informed conversations with patients about getting vaccinated.

Influenza knowledge and barriers to vaccination in immunosuppressed patients in the pediatric rheumatology clinic

BACKGROUND

Most patients with a pediatric rheumatic disease are at increased risk of influenza due to immunosuppressive medication use. Despite initial quality improvement efforts, our influenza vaccination rate plateaued at 72%, which prompted a survey of patients and families to assess provider vaccine recommendations, influenza knowledge, and barriers to influenza vaccination.

METHODS

Patients on immunosuppressive medication or their parent were eligible to complete a survey between July 2019 and January 2020. Survey questions assessed demographics, rheumatology diagnosis, immunosuppressive medication(s), influenza vaccination recommendation, patient/parent influenza knowledge, and barriers to influenza vaccination. Influenza vaccination rates for immunosuppressed patients were acquired each influenza season from 2015-2020 and tracked on a control chart.

RESULTS

Of the 226 completed surveys, 145 (64.2%) were completed by parents and 81 (35.8%) by patients. The majority (85%) reported the influenza vaccine was recommended. The most common reasons for not receiving the influenza vaccine included: worry about disease flare (25.6%), concern the vaccine will cause influenza (25.6%), and lack of vaccine effectiveness (20.5%). Parents (40.9%) were more worried about disease flare compared to patients (17%; p = 0.024). Most respondents were able to correctly answer fever, cough and/or congestion as the most common symptoms of influenza; however, 23% answered gastrointestinal symptoms and 10.2% joint swelling. Most respondents (95.1%) were aware that immunosuppressive medication increases risk of infection. The average weekly influenza vaccination rate for the 2019-2020 flu season was 85.5%, which increased from 72.0% the previous year. Parents with higher education status were more likely to have their child receive the influenza vaccine compared to parents with less education.

CONCLUSIONS

This survey indicates that respondents understand the potential severity of influenza and the increased risk of infection due to immunosuppressive medication use; however, many inaccurately identified the most common symptoms of influenza and also reported misconceptions of influenza vaccine risks. The barriers identified in this survey will help drive future improvement efforts to increase influenza vaccination rates in this high-risk population.

Recent advances in the influenza virus vaccine landscape: a comprehensive overview of technologies and trials

SUMMARYIn the United Kingdom (UK) in 2022/23, influenza virus infections returned to the levels recorded before the COVID-19 pandemic, exerting a substantial burden on an already stretched National Health Service (NHS) through increased primary and emergency care visits and subsequent hospitalizations. Population groups ≤4 years and ≥65 years of age, and those with underlying health conditions, are at the greatest risk of influenza-related hospitalization. Recent advances in influenza virus vaccine technologies may help to mitigate this burden. This review aims to summarize advances in the influenza virus vaccine landscape by describing the different technologies that are currently in use in the UK and more widely. The review also describes vaccine technologies that are under development, including mRNA, and universal influenza virus vaccines which aim to provide broader or increased protection. This is an exciting and important era for influenza virus vaccinations, and advances are critical to protect against a disease that still exerts a substantial burden across all populations and disproportionately impacts the most vulnerable, despite it being over 80 years since the first influenza virus vaccines were deployed.

Consensus on COVID-19 vaccine recommendations: Challenges and strategies for high-risk populations in Taiwan

The COVID-19 pandemic has had a profound impact globally, particularly in high-risk populations such as those with underlying health conditions. In response to the evolving pandemic landscape and the recent surge in confirmed cases in Taiwan, the Taiwan Association of Family Medicine (TAFM) established a consensus on COVID-19 vaccine recommendations for vulnerable groups through a comprehensive literature review, expert panel discussions, and a practice-oriented formulation procedure to develop evidence-based guidance. Its key findings highlight the increased risk of severe COVID-19 outcomes among individuals with disorders such as diabetes, obesity, chronic kidney disease, cardiovascular disease, and respiratory illness. It emphasizes the safety and effectiveness of COVID-19 vaccines, particularly mRNA vaccines, in these high-risk populations. It particularly underscores the critical role of family medicine physicians in the COVID-19 response, including routine screening, health education, vaccination delivery, and continuous research to optimize strategies. Ongoing monitoring, adaptation, and collaborative efforts will be essential to ensure the continued effectiveness of these recommendations in the evolving COVID-19 landscape. In conclusion, the TAFM consensus recommendations provide a robust framework to guide healthcare providers and policymakers in tailoring vaccination efforts to address the unique needs of vulnerable groups in Taiwan and are an applicable template for neighboring countries.

Relative effectiveness of adjuvanted versus non-adjuvanted influenza vaccines in older adults with risk factors for influenza complications during the 2019-2020 U.S. influenza season

This study estimated the relative vaccine effectiveness (rVE) of the MF59®-adjuvanted trivalent influenza vaccine (aTIV) versus standard-dose nonadjuvanted egg-based quadrivalent influenza vaccines (QIVe) for the prevention of influenza-related medical encounters (IRMEs), outpatient IRMEs, and influenza- and pneumonia-related hospitalizations during the 2019-2020 US influenza season among adults ≥65 years of age who had ≥1 high-risk condition. A secondary objective evaluated the rVE of aTIV versus QIVe in preventing these outcomes among older adults with specific high-risk conditions. This retrospective cohort study included US adults ≥65 years of age vaccinated with aTIV or QIVe between August 1, 2019, and January 31, 2020. Exposures, covariates, risk factors, and outcomes were captured from a linked dataset comprised of electronic health records (EHR) (Veradigm Network EHR) linked to insurance claims (Komodo Healthcare Map). A doubly robust approach was applied wherein multivariable-adjusted odds ratios were derived using inverse probability of treatment-weighted samples to calculate rVEs and 95 % confidence interval independently for individuals ≥1 high-risk condition and those with specific high-risk conditions. The study included 954,707 aTIV and 719,125 QIVe recipients. For all outcomes, aTIV was more effective than QIVe among adults ≥65 years of age who had ≥1 high-risk condition (any IMRE: 23.6 % [20.9 %-26.1 %]), outpatient IRME: 23.3 % [20.4 %-26.1 %], and influenza- or pneumonia-related hospitalizations: 19.0 % [16.3 %-21.6 %]), during the 2019-2020 influenza season. Similarly, aTIV was more effective than QIVe at preventing outcomes among individuals with specific high-risk conditions except for body mass index ≥40. This study demonstrated higher effectiveness of aTIV versus QIVe in preventing any IRMEs, outpatient IRMEs, and influenza- or pneumonia-related hospitalizations among adults ≥65 years of age who had ≥1 high-risk condition.

Estimating influenza vaccine effectiveness among older adults using an integrated administrative database and the implications of potential bias: A population-based cohort study in Japan

BACKGROUND

Japan lacks an established framework for routine seasonal influenza vaccine effectiveness (SIVE) assessment at the national and municipal levels. This study aimed to estimate SIVE among older adults using an innovative population-based administrative database linking medical fee claims data with vaccination records, while also exploring its potential bias.

METHODS

In this retrospective population-based cohort study, we assessed SIVE against medically attended influenza during the 2017/18 season among older adults aged ≥65 years in a Japanese city. A Cox proportional hazards model was used to estimate hazard rate ratios, treating vaccination status as time-dependent. To explore potential biases, multivariate logistic regression analysis was used to investigate the association between vaccination status and acute respiratory infection (ARI) diagnosis and trauma/injury during the non-influenza season.

RESULTS

This study included 82 % (n = 110,892) of the city's older adult population, with 39.7 % vaccination coverage. The estimated SIVE was 2.9 % (95 % confidence interval: -6.2-11.2), showing no statistical significance. Similarly, subgroup analyses by age and comorbidities revealed no significant protective effect of SIVE. In the non-season analysis, adjusted odds ratios of vaccination were significantly higher for ARI [1.3 (1.3-1.4)] and trauma/injury [1.2 (1.1-1.2)]. However, no significance was observed for hospitalizations with these diagnoses, which include severe conditions less associated with healthcare-seeking behaviors [0.9 (0.8-1.1) and 0.8 (0.6-1.0), respectively].

CONCLUSIONS

No significant SIVE was observed during the 2017/18 season. Our real-world observational study, based on medical fee claims data, indicates a potential underestimation of SIVE owing to bias related to healthcare-seeking behaviors.

The clinical and economic value of enhanced influenza vaccines for the elderly in Argentina

Background

Enhanced influenza vaccines are the best option for the elderly. In 2021, Argentina introduced the MF59-adjuvanted inactivated influenza vaccine (aIIV) for individuals aged 65 years. and above, in the national immunization program. High dose inactivated influenza vaccine (HD-IIV) is also currently registered. This study evaluates the clinical and economic outcomes of these noted enhanced influenza vaccines for the elderly in Argentina.

Methods

Using a static decision-tree model and adopting the payer's perspective during an average influenza season, the analysis incorporated influenza epidemiological data from pre-pandemic Argentinian seasons (2014-2019), strain distribution, vaccination uptake, influenza-related costs and Quality-Adjusted Life-Years (QALYs) gained. Results include two relative vaccine effectiveness (rVE) scenarios from two published meta-analyses, due to reported rVE variability, although without statistical significance expected between enhanced vaccines. Vaccination acquisition costs were obtained from aIIV manufacturer, while HD-IIV costs were estimated using local (Argentinian private sector) and international public sector data (Europe). This assessment considered one GDP per-capita (US$13,696) as a cost-effectiveness threshold and included multiple sensitivity analysis.

Results

With an expected lower vaccine cost and non-significant higher rVE for aIIV vs HD-IIV (3.2 %), aIIV generated 41.4 QALYs gained and US$8.7 M savings to the Argentinean public health system. In this scenario aIIV resulted as a dominant strategy over HD-IIV. On a second scenario, where HD-IIV has a non-significant higher rVE compared to aIIV (15.9 % and 13.9 % for HD-IIV and aIIV, respectively, both vs standard-dose IIV), HD-IIV would only result cost-effective compared to aIIV if its public price is up to 25 % the incremental cost in relation to the standard-dose IIV acquisition price.

Conclusions

In Argentina, the use of enhanced influenza vaccines in the elderly can increase vaccine effectiveness, reduce mortality and disease-related costs. Based on comparable effectiveness, the economic advantage of aIIV over HD-IIV confirms the current vaccination strategy employing aIIV in Argentina.

Protection against influenza hospitalizations from enhanced influenza vaccines among older adults: A systematic review and network meta-analysis

BACKGROUND

Influenza vaccines are available to help protect persons aged ≥65 years, who experience thousands of influenza hospitalizations annually. Because some influenza vaccines may work better than others, we sought to assess benefit of high-dose (HD), adjuvanted (ADJ), and recombinant (RIV) influenza vaccines ("enhanced influenza vaccines") compared with standard-dose unadjuvanted influenza vaccines (SD) and with one another for prevention of influenza-associated hospitalizations among persons aged ≥65 years.

METHODS

We searched MEDLINE, Embase, CINAHL, Scopus, and Cochrane Library to identify randomized or observational studies published between January 1990 and October 2023 and reporting relative vaccine effectiveness (rVE) of HD, ADJ, or RIV for prevention of influenza-associated hospitalizations among adults aged ≥65 years. We extracted study data, assessed risk of bias, and conducted random-effects network meta-analysis and meta-regression.

RESULTS

We identified 32 studies with 90 rVE estimates from five randomized and 27 observational studies (71,459,918 vaccinated participants). rVE estimates varied across studies and influenza seasons. Pooled rVE from randomized studies was 20% (95% CI -54 to 59) and 25% (95% CI -19 to 53) for ADJ and HD compared with SD, respectively; rVE was 6% (95% CI -109 to 58) for HD compared with ADJ; these differences were not statistically significant. In observational studies, ADJ, HD, and RIV conferred modestly increased protection compared with SD (rVE ranging from 10% to 19%), with no significant differences between HD, ADJ, and RIV. With enhanced vaccines combined, rVE versus SD was 18% (95% CI 3 to 32) from randomized and 11% (95% CI 8 to 14) from observational evidence. Meta-regression of observational studies suggested that those requiring laboratory confirmation of influenza reported greater benefit of enhanced vaccines.

CONCLUSIONS

HD, ADJ, and RIV provided stronger protection than SD against influenza hospitalizations among older adults. No differences in benefit were observed in comparisons of enhanced influenza vaccines with one another.

Safety and immunogenicity of mRNA-1345 RSV vaccine coadministered with an influenza or COVID-19 vaccine in adults aged 50 years or older: an observer-blinded, placebo-controlled, randomised, phase 3 trial

BACKGROUND

Coadministration of a respiratory syncytial virus (RSV) vaccine with seasonal influenza or SARS-CoV-2 vaccines could reduce health-care visits and increase vaccination uptake in older adults who are at high risk for severe respiratory disease. The RSV mRNA-1345 vaccine demonstrated efficacy against RSV disease with acceptable safety in the ConquerRSV trial in adults aged 60 years and older. We aimed to evaluate the safety and immunogenicity of mRNA-1345 coadministered with a seasonal influenza vaccine or SARS-CoV-2 mRNA vaccine.

METHODS

We conducted a two-part, phase 3, observer-blinded, placebo-controlled, randomised trial in medically stable adults aged 50 years or older in the USA. In part A, participants were randomly assigned in a 7:10:10 ratio to receive 50 μg mRNA-1345 plus placebo (0·9% sodium chloride) or coadministered with 60 μg of a standard-dose quadrivalent inactivated influenza vaccine (SIIV4), or SIIV4 plus placebo. In part B, participants were randomly assigned in a 1:1:1 ratio to receive 50 μg mRNA-1345 plus placebo or coadministered with 50 μg SARS-CoV-2 mRNA-1273.214 (bivalent [Wuhan-Hu-1 plus omicron BA.1]), or mRNA-1273.214 plus placebo. Random allocation in both parts was stratified by age group (50-59 years, 60-74 years, and ≥75 years) and used interactive response technology. The coprimary objectives in each part were safety in the safety set throughout the study and non-inferiority for six immunogenicity endpoints in the per-protocol set comparing coadministered versus individual vaccines on day 29. Immunogenicity endpoints were geometric mean titre (GMT) ratios (GMRs) of RSV-A neutralising antibodies (nAbs; in parts A and B), GMRs of haemagglutination inhibition (HAI) titres to each of the four influenza strains in SIIV4 (A/Victoria/2570/2019 [H1N1]pdm09-like virus [A/H1N1], A/Cambodia/e0826360/2020 [H3N2]-like virus [A/H3N2], B/Washington/02/2019-like virus [B/Victoria], and B/Phuket/3073/2013-like virus [B/Yamagata]; in part A), GMRs of nAbs against SARS-CoV-2 (ancestral [D614G] and omicron BA.1; part B), and differences in seroresponse rates for nAbs against RSV-A (parts A and B) and SARS-CoV-2 (ancestral [D614G] and omicron BA.1; part B). Non-inferiority was declared when the lower bound of the 95% CI for GMRs was greater than 0·667 and for seroresponse rate differences was greater than -10%. This trial is registered with ClinicalTrials.gov (NCT05330975) and is ongoing.

FINDINGS

Between April 1 and June 9, 2022, 1631 participants were randomly allocated in part A and 1623 received vaccinations on day 1 (685 [42%] received mRNA-1345 plus SIIV4, 249 [15%] mRNA-1345 plus placebo, and 689 [42%] SIIV4 plus placebo). Due to an interactive response technology error, the mRNA-1345 plus placebo group was smaller than planned (249 vs 420 participants). Of the 1623 participants in the safety set, 877 (54%) were female and 746 (46%) were male. Between July 27 and Sept 28, 2022, 1691 participants were randomly allocated in part B and 1681 received vaccinations on day 1 (564 [34%] received mRNA-1345 plus mRNA-1273.214, 558 [33%] mRNA-1345 plus placebo, and 559 [33%] mRNA-1273.214 plus placebo). Among the 1681 participants in the safety set, 924 (55%) were female and 757 (45%) were male. The reactogenicity profiles of the coadministered regimens were generally similar to the profiles when the vaccines were administered alone. As of the 6-month and 7-month follow-up times for parts A and B, respectively, no serious adverse events, adverse events of special interest, discontinuations due to adverse events, or fatal events considered related to study vaccination were reported. In part A, the GMR of nAbs against RSV-A in the mRNA-1345 plus SIIV4 group versus the mRNA-1345 alone group was 0·81 (95% CI 0·67 to 0·97), and the seroresponse rate difference in nAbs against RSV-A between the groups was -11·2% (95% CI -17·9 to -4·1). GMRs of anti-HAI titres in the mRNA-1345 plus SIIV4 versus SIIV4 alone groups were 0·89 (0·77 to 1·03) for A/H1N1, 0·97 (0·86 to 1·09) for A/H3N2, 0·93 (0·82 to 1·05) for B/Victoria, and 0·91 (0·81 to 1·02) for B/Yamagata. In part B, the GMR of nAbs against RSV-A in the mRNA-1345 plus mRNA-1273.214 versus the mRNA-1345 alone groups was 0·80 (95% CI 0·70 to 0·90), and the seroresponse rate difference was -4·4% (95% CI -9·9 to 1·0). Comparing the mRNA-1345 plus mRNA-1273.214 group with the mRNA-1273.214 alone group, the GMR of nAbs was 0·96 (0·87 to 1·06) for the ancestral (D614G) virus and 1·00 (0·89 to 1·14) for omicron BA.1; seroresponse rate differences were 0·2% (95% CI -6·0 to 6·3) for SARS-CoV-2 ancestral and -0·9% (-6·6 to 4·7) for omicron BA.1.

INTERPRETATION

Coadministered mRNA-1345 plus SIIV4 or mRNA-1273.214 vaccines had acceptable safety profiles and elicited mostly non-inferior immune responses compared to individual vaccines in adults aged 50 years or older; only the seroresponse rate difference in nAbs against RSV-A in part A did not meet the non-inferiority criterion. Overall, these data support coadministration of mRNA-1345 with these vaccines in this population; longer-term evaluation continues in this study.

FUNDING

Moderna.

A Modified Novel Validated High-Throughput Hemagglutinin Inhibition Assay Using Recombinant Virus-like Particles and Human Red Blood Cells for the Objective Evaluation of Recombinant Hemagglutinin Nanoparticle Seasonal Influenza Vaccine

Currently available seasonal influenza vaccines confer variable protection due to antigenic changes resulting from the accumulation of diverse mutations. The analysis of new seasonal influenza vaccines is challenging in part due to the limitations of the traditional hemagglutination inhibition (HAI) assay with A/H3N2 strains. An improved and objective novel HAI assay was developed with recombinant virus-like particles (VLPs) and an egg-derived virus as agglutinins, the oseltamivir treatment of VLPs, human red blood cells, and using an automated image reader-based analysis of hemagglutination. HAI validation was demonstrated using four VLPs and egg-derived strains, with 46-56 serum samples tested 12 times in duplicate per strain. The validated HAI assay was precise as indicated by the percent geometric coefficient of variation for intra-, inter-, and total assay precision, as well as accurate as evidenced by percent bias measurements. The assay exhibited linearity, specificity for homologous type/subtype strains, and sensitivity with a starting dilution of 1:10. Assay robustness and sample stability were demonstrated as a percentage difference compared to reference condition. Validated HAI results were equivalent for the single and duplicate sample testing and correlated well with a qualified live wild-type influenza microneutralization assay. These findings demonstrate the suitability of this high-throughput novel modified validated HAI assay for evaluating vaccine immunogenicity and efficacy.

Prokaryote- and Eukaryote-Based Expression Systems: Advances in Post-Pandemic Viral Antigen Production for Vaccines

This review addresses the ongoing global challenge posed by emerging and evolving viral diseases, underscoring the need for innovative vaccine development strategies. It focuses on the modern approaches to creating vaccines based on recombinant proteins produced in different expression systems, including bacteria, yeast, plants, insects, and mammals. This review analyses the advantages, limitations, and applications of these expression systems for producing vaccine antigens, as well as strategies for designing safer, more effective, and potentially 'universal' antigens. The review discusses the development of vaccines for a range of viral diseases, excluding SARS-CoV-2, which has already been extensively studied. The authors present these findings with the aim of contributing to ongoing research and advancing the development of antiviral vaccines.

Pediatric practice experiences with second dose influenza vaccination: An AAP Pediatric Research in Office Settings (PROS) Study

OBJECTIVES

Explore pediatric staff experiences administering the second influenza vaccine dose.

STUDY DESIGN

Qualitative focus groups/interviews.

METHODS

As part of the National Institutes of Health-funded Flu2Text randomized control trial of text message reminders for second influenza vaccine dose, we conducted seven focus groups and four individual interviews (n = 39 participants total) with clinicians and staff from participating practices from the American Academy of Pediatrics' Pediatric Research in Office Settings (PROS) Network. Of 37 participating practices, 10 were selected through stratified sampling of practices with highest (n = 5) and lowest (n = 5) randomized controlled trial effect sizes. A semi-structured discussion guide included questions that addressed parental, practice, and health system barriers/facilitators to second influenza vaccine dose administration. Using the Systems Model of Clinical Preventive Care as a conceptual framework, two investigators independently coded transcripts (Κ = 0.86, high agreement) with NVivo 12 Plus. Coding inconsistencies were resolved by consensus.

RESULTS

Clinicians/staff reported that administering the second influenza vaccine dose in a season was more complex than other childhood vaccines. They highlighted parental uncertainty about the need for the second dose and the difficulty and inconvenience of bringing children back to the office as important barriers. Caregiver-staff relationships were perceived as helpful in getting children vaccinated with their second dose and vaccine reminders were seen as important cues-to-action.

CONCLUSIONS

Ensuring receipt of two doses of the influenza vaccine in a given season presents unique challenges. Themes identified provide a framework for understanding opportunities to bolster second dose receipt, including explaining why two doses are needed, offering flexible hours for vaccination, and sending vaccine reminders.

Time of day for vaccination, outcomes, and relative effectiveness of high-dose vs. standard-dose quadrivalent influenza vaccine: A post hoc analysis of the DANFLU-1 randomized clinical trial

OBJECTIVES

Morning influenza vaccination enhances antibody response. In this post hoc analysis of the DANFLU-1 trial, we sought to evaluate the association between time of day for vaccination (ToV) and outcomes and whether ToV modified the relative effectiveness of high-dose (QIV-HD) vs. standard-dose (QIV-SD) quadrivalent influenza vaccine.

METHODS

DANFLU-1 was a pragmatic feasibility trial of QIV-HD vs. QIV-SD. Outcomes included hospitalizations and mortality. For subgroup analysis, the population was dichotomized at median ToV into two groups (early and late).

RESULTS

The study population included 12,477 participants. Mean age was 71.7 ± 3.9 years with 5877 (47.1%) female participants. Median ToV was 11.29 AM. Earlier ToV was associated with fewer respiratory hospitalizations independent of vaccine type, which persisted in adjusted analysis (IRR 0.88 per 1-hour decrement (95% CI 0.78- 0.98, p = 0.025). No effect modification by continuous or dichotomous ToV was found. In subgroup analysis, effects consistently favored QIV-HD against hospitalizations for pneumonia or influenza (early: IRR 0.30; late: 0.29), all-cause hospitalizations (early: IRR 0.87; late: 0.86), and mortality (early: HR 0.53; late: 0.50).

CONCLUSION

In this exploratory post hoc analysis, earlier ToV was associated with fewer respiratory hospitalizations. The relative effectiveness of QIV-HD vs. QIV-SD was not modified by ToV. Further research is needed to confirm findings.

TRIAL REGISTRATION

Clinicaltrials.gov: NCT05048589.

Safety of quadrivalent recombinant influenza vaccine in pregnant persons and their infants

Background

The Advisory Committee on Immunization Practices (ACIP) and the American College of Obstetricians and Gynecologists (ACOG) recommend that all pregnant persons receive any licensed, recommended, and age-appropriate inactivated influenza vaccine (SD-IIV) or recombinant influenza vaccine (RIV) to protect against influenza and influenza-related complications. RIV was safe and efficacious in pre- and postlicensure studies, however there is limited RIV safety data in pregnant persons.

Objective

To evaluate the safety of quadrivalent recombinant influenza vaccine (RIV4) versus a quadrivalent standard-dose, inactivated influenza (SD-IIV4) in a large cohort of pregnant persons and their infants.

Study Design

This postlicensure observational safety study conducted at Kaiser Permanente Northern California evaluated the subset of pregnant persons vaccinated in routine care as part of a larger cluster-randomized vaccine effectiveness study comparing RIV4 vs. SD-IIV4 (ClinicalTrials.gov NCT03694392). We identified pregnancy (spontaneous abortion, preterm labor, stillbirth/fetal death, congenital/fetal anomalies detected during pregnancy, eclampsia/pre-eclampsia, placental abruption), birth (preterm birth, low birth weight, small for gestational age), and neonatal/infant outcomes (infant death, failure to thrive, congenital anomalies detected after delivery) using diagnostic codes among pregnant persons ≥18 years immunized with RIV4 or SD-IIV4 during the 2018/19 and 2019/20 influenza seasons and their infants. We used conditional logistic regression adjusted for age group, race, ethnicity, trimester of influenza vaccination, comorbidities, and BMI, stratified by gestational age to estimate the odds ratio (OR) of pregnancy outcomes following vaccination with RIV4 vs. SD-IIV4. Using logistic regression, we separately estimated the adjusted OR of birth and neonatal/infant outcomes in the first year of life (eg, death) in infants of RIV4 vs. SD-IIV4 vaccinated pregnant persons.

Results

The study population included 48,781 pregnant persons (RIV4 = 14,981; SD-IIV4 = 33,800) and 47,394 live births (RIV4 = 14,538; SD-IIV4 = 32,856). There was no statistical difference in any pregnancy outcome or in birth and neonatal/infant outcome between RIV4 vs. SD-IIV4 vaccinated pregnant persons and their infants.

Conclusion

Compared with receipt of a SD-IIV4 during pregnancy, this large study did not identify any pregnancy, birth, or neonatal/infant safety concerns following receipt of a RIV4 during pregnancy and demonstrates that the safety of RIV4 in pregnancy was similar to SD-IIV4. This study provides additional evidence regarding the safety of influenza vaccination in pregnant persons and further supports ACIP and ACOG recommendations that all pregnant persons receive an inactivated or recombinant influenza vaccine.

Vaccinations in older adults: Optimization, strategies, and latest guidelines

This article is a summary of the first AGS Symposium entitled "Update on Vaccination Strategies for Older Adults: Matching the Approach to the Individual and the Care Setting." Given declines in host defenses and immune function with aging, vaccinations play a pivotal role in fortifying older adults against preventable infections, resulting diseases, disability, and death. Current guidelines generally list recommendations applicable for an average older adult of a given chronological age. However, growing evidence indicates that heterogeneity in terms of factors as varied as biological sex, frailty, functional status, and multimorbidity may impact vaccine responses and clinical outcomes. As a result, clinicians will increasingly need to take these additional factors into consideration as they seek to improve outcomes through improved targeting of such aging-related heterogeneity. Moreover, efforts at protecting older citizens through vaccination must also include strategies to overcome barriers to the adoption of vaccine recommendations in varied settings including long-term care. This 2023 AGS Plenary Symposium sought to commence a broader dialogue across AGS and beyond on optimizing vaccinations for older adults, ensuring not only extended lifespans but also healthier and more active lives. This report is not a systematic review, and thus should not be considered comprehensive.

Costs of in- and outpatient respiratory disease and the seasonal influenza vaccination program in Armenia - 2020-2021

BACKGROUND

Despite the substantial global impact of influenza, there are limited economic data to guide influenza vaccination programs investments in middle-income countries. We measured the costs of influenza and the costs of an influenza vaccination program in Armenia, using a societal perspective.

METHODS

During December 2022 through March 2023, retrospective cost data were collected from case-patients and healthcare providers through structured questionnaires at 15 healthcare facilities selected through stratified sampling. Medical costs included medications, laboratory costs, laboratory and diagnostic tests, and routine health care service costs and direct and indirect societal costs were included. Vaccination program costs from the 2021-2022 influenza season were identified using accounting records and categorized as: planning, distribution, training, social mobilization and outreach, supervision and monitoring, procurement, and national- and facility-level administration and storage.

RESULTS

The mean costs per episode for SARI and ILI case-patients were $US 823.6 and $US 616.57, respectively. Healthcare service costs were the largest direct expenses for ILI and SARI case-patients. Total costs of the 2021-2022 influenza vaccination program to the government were $US 4,353,738, with the largest costs associated with national- and facility-level administration and storage (30% and 65% respectively). The total cost per dose administered was $US 25.61 ($US 7.73 per dose for procurement and $US 17.88 for the marginal administration cost per dose).

CONCLUSIONS

These data on the costs of seasonal influenza prevention programs and the societal costs of influenza illness in Armenia may inform national vaccine policy decisions in Armenia and may be useful for other middle-income countries. Influenza vaccines, like other vaccine programs, are recognized as substantially contributing to the reduction disease burden and associated mortality and further driving economic growth. However, a formal cost-effectiveness analysis should be performed once burden of disease data are available.

Safety and Immunogenicity of Respiratory Syncytial Virus Prefusion F Protein Vaccine when Co-administered with Adjuvanted Seasonal Quadrivalent Influenza Vaccine in Older Adults: A Phase 3 Randomized Trial

BACKGROUND

We evaluated co-administration of adjuvanted seasonal quadrivalent influenza vaccine (FLU-aQIV) and respiratory syncytial virus (RSV) prefusion F protein-based vaccine (RSVPreF3 OA) in ≥65-year-olds.

METHODS

This phase 3, open-label trial randomized ≥65-year-olds to receive FLU-aQIV and RSVPreF3 OA concomitantly (Co-Ad) or sequentially, 1 month apart (Control). Primary objectives were to demonstrate the non-inferiority of FLU-aQIV and RSVPreF3 OA co-administration versus sequential administration in terms of hemagglutination inhibition (HI) titers for each FLU-aQIV strain and RSV-A and RSV-B neutralization titers, 1 month post-vaccination. Reactogenicity and safety were also assessed.

RESULTS

Overall, 1045 participants were vaccinated (Co-Ad: 523; Control: 522). Non-inferiority of FLU-aQIV and RSVPreF3 OA co-administration versus sequential administration was demonstrated in terms of HI titers for the A/Victoria(H1N1), B/Victoria, and B/Yamagata influenza strains and RSV-A neutralization titers (upper limits [ULs] of 95% confidence intervals [CIs] for adjusted geometric mean titer [GMT] ratios [Control/Co-Ad] ≤1.50) but not for A/Darwin(H3N2) HI titers (95% CI UL = 1.53). The immune response to A/Darwin(H3N2) was further assessed post-hoc using a microneutralization assay; the post-vaccination adjusted GMT ratio (Control/Co-Ad) was 1.23 (95% CI: 1.06-1.42, ie, UL ≤1.50), suggesting an adequate immune response to A/Darwin(H3N2) following co-administration. RSV-B neutralization titers were comparable between groups (95% CI UL for adjusted GMT ratio ≤1.50). Solicited adverse events were mostly mild or moderate and transient; unsolicited and serious adverse event rates were balanced between groups.

CONCLUSIONS

Adjuvanted FLU-aQIV and RSVPreF3 OA had acceptable reactogenicity/safety profiles when co-administered in ≥65-year-olds, without clinically relevant interference with the immune responses to either vaccine.

CLINICAL TRIALS REGISTRATION

NCT05568797.

Immunization in women's lives: present and future

•The negative impact of infectious diseases and their immunoprevention during the different stages of a woman's life requires a broad approach including adolescence, adulthood, pregnancy and the postmenopausal phase. •Immunization of pregnant women should be a priority for the protection of the maternal-fetal dyad, especially in regions with high rates of infections preventable by immunization. •Brazil has one of the most comprehensive vaccination programs in the world - the National Immunization Program (Programa Nacional de Imunizações, PNI) - that serves all age groups: newborns, children, adolescents, adults, pregnant women and older adults, as well as groups with special needs, such as adolescents, pregnant and older adult women. •However, vaccination coverage remains below ideal for all available vaccines, especially among adolescents and pregnant women, and Febrasgo is committed to collaborating with the PNI to combat vaccine hesitancy. •The gynecologist/obstetrician is the reference physician for women, therefore the access to information and updates regarding all vaccines recommended for their patients is extremely important for this professional, aiming at the greatest possible protection. •The objective of this Febrasgo Position Statement is to bring an update to women's vaccination schedule, covering some vaccines that are available, including new approved vaccines and those in the commercialization phase. •This work is a compilation of the First Febrasgo Scientific Immunization Forum held in the city of São Paulo in October 2023 with the objective to update recommendations for vaccines in use and new innovative vaccines soon to be available.

Interim Effectiveness Estimates of 2024 Southern Hemisphere Influenza Vaccines in Preventing Influenza-Associated Hospitalization - REVELAC-i Network, Five South American Countries, March-July 2024

To reduce influenza-associated morbidity and mortality, countries in South America recommend annual influenza vaccination for persons at high risk for severe influenza illness, including young children, persons with preexisting health conditions, and older adults. Interim estimates of influenza vaccine effectiveness (VE) from Southern Hemisphere countries can provide early information about the protective effects of vaccination and help guide Northern Hemisphere countries in advance of their season. Using data from a multicountry network, investigators estimated interim VE against influenza-associated severe acute respiratory illness (SARI) hospitalization using a test-negative case-control design. During March 13-July 19, 2024, Argentina, Brazil, Chile, Paraguay, and Uruguay identified 11,751 influenza-associated SARI cases; on average, 21.3% of patients were vaccinated against influenza, and the adjusted VE against hospitalization was 34.5%. The adjusted VE against the predominating subtype A(H3N2) was 36.5% and against A(H1N1)pdm09 was 37.1%. These interim VE estimates suggest that although the proportion of hospitalized patients who were vaccinated was modest, vaccination with the Southern Hemisphere influenza vaccine significantly lowered the risk for hospitalization. Northern Hemisphere countries should, therefore, anticipate the need for robust influenza vaccination campaigns and early antiviral treatment to achieve optimal protection against influenza-associated complications.

Influenza epidemiology and vaccine effectiveness during the 2023/2024 season in Italy: A test-negative case-control study

OBJECTIVES

In order to support policymakers in allocating resources, we aimed to assess vaccine effectiveness (VE) of inactivated influenza vaccines (IIVs) available for Italian adults in the 2023/2024 season.

METHODS

A hospital-based test-negative case-control study was conducted in Genoa between mid-October 2023 and mid-April 2024. Adult (≥18 years) inpatients with prescription of a polymerase chain reaction test for influenza were eligible.

RESULTS

Of 1,664 adults analyzed, most (82%) of which were ≥65 years, 114 (6.9%) tested positive for influenza A. Most (92%) cases were caused by subclades 6B.1A.5a.2a and 6B.1A.5a.2a.1 of the A(H1N1)pdm09 subtype. In older adults aged ≥65 years vaccination was effective at 51% (95% CI: 8%, 74%) against any influenza A and 49% (95% CI: 2%, 73%) against A(H1N1)pdm09. Compared with non-vaccinated older adults, VE point estimates for the adjuvanted and, especially, high-dose IIVs were higher than those for the standard-dose non-adjuvanted IIV.

CONCLUSION

The 2023/2024 seasonal influenza vaccination proved moderately effective in preventing hospitalization for laboratory-confirmed influenza. Being more appropriate for older adults, local policymakers and vaccinating physicians should maximize adoption of the enhanced IIVs.

Postpartum Interventions to Increase Maternal Vaccination Uptake: Is It Worth It?

BACKGROUND/OBJECTIVES

Vaccination of pregnant and postpartum women for pertussis, influenza and COVID-19 not only protects themselves but also offspring. Despite the benefits of this approach, vaccination uptake remains suboptimal in pregnancy. Where the opportunity to be vaccinated in pregnancy is missed, the offer of vaccination in the post-partum period may be an alternative strategy. The aim of this systematic review is to assess the impact of interventions to increase vaccination uptake in the postpartum period on vaccination uptake.

METHODS

A literature search was performed in MEDLINE, including interventional studies promoting vaccination uptake in postpartum women published between 2009 and 2024. The search was conducted according to PRISMA guidelines and registered with PROSPERO.

RESULTS

We finally included 16 studies in the review, and the primary outcome was vaccination uptake in the postpartum period. The most significant factors for increasing uptake were recommendation from healthcare providers, type of interventions used, and delivery of vaccines in the maternity wards or the community.

CONCLUSIONS

In conclusion, maternal vaccination rates in the postpartum period may increase with targeted education by healthcare professionals and positive reinforcement. The interventions described in these studies could be applied in the healthcare systems worldwide.

Safety of Simultaneous Vaccination With Adjuvanted Zoster Vaccine and Adjuvanted Influenza Vaccine: A Randomized Clinical Trial

Importance

Quadrivalent adjuvanted inactivated influenza vaccine (aIIV4) and adjuvanted recombinant zoster vaccine (RZV) contain novel adjuvants. Data are limited on the comparative safety, reactogenicity, and health-related quality of life (HRQOL) effects of the simultaneous administration of these vaccines.

Objective

To compare the safety and reactogenicity after simultaneous doses of RZV and aIIV4 administration (opposite arms) with simultaneous doses of RZV with quadrivalent high-dose inactivated influenza vaccine [HD-IIV4]).

Design, Setting, and Participants

This randomized blinded clinical trial was conducted during the 2021-2022 and 2022-2023 influenza seasons at 2 centers in the US among community-dwelling adults aged 65 years or older. Analysis was performed on an intention-to-treat basis.

Intervention

Simultaneous intramuscular administration of RZV dose 1 and aIIV4 or HD-IIV4 in opposite arms after age stratification (65-69 and ≥70 years) and randomization.

Main Outcomes and Measures

The primary outcome was the proportions of participants with 1 or more severe solicited reactions during days 1 to 8, using a noninferiority test (10% noninferiority margin). Additional measures included serious adverse events and adverse events of clinical interest during days 1 to 43 of the study period.

Results

A total of 267 adults (median age, 71 years [range, 65-92 years]; 137 men [51.3%]) were randomized; 130 received simultaneous RZV and aIIV4, and 137 received simultaneous RZV and HD-IIV4. The proportion of patients reporting 1 or more severe reactions after simultaneous administration of RZV and aIIV4 (15 of 115 [11.5%]) was noninferior compared with simultaneous RZV and HD-IIV4 (17 of 119 [12.5%]) (absolute difference, -1.0% [95% CI, -8.9% to 7.1%]). There were no significant differences in the number of serious adverse events or adverse events of clinical interest between the groups.

Conclusions and Relevance

In this clinical trial of simultaneous doses of RZV and aIIV4 compared with simultaneous doses of RZV and HD-IIV4, overall safety findings were similar between groups. From a safety standpoint, this study supports the simultaneous administration of RZV and aIIV4 among older adults.

Trial Registration

ClinicalTrials.gov Identifier: NCT05007041.

Flu-Phobia: Influenza Vaccine Hesitancy in a Rural Primary Care Setting

The sentiments expressed by individuals, such as "I do not trust vaccines," "I do not believe in vaccines," and "I do not want a shot," are commonly encountered by physicians during the annual influenza season. This study investigates vaccine hesitancy regarding the influenza vaccine within a rural primary care setting in New York State. Observations of subjective comments from community members prompted an inquiry into whether the contentious discourse surrounding the COVID-19 vaccine has influenced patients' decisions about the influenza vaccination. We hypothesized that over 50% of patients would decline the influenza vaccine during the 2023-2024 season and that many would attribute their refusal to the controversies associated with the COVID-19 vaccine. The findings of the study revealed that while more than 50% of surveyed patients did indeed refuse the influenza vaccine, only a minority linked their decision to the COVID-19 vaccine controversy. This paper examines the attitudes of a rural community toward the influenza vaccine and proposes potential strategies to address future vaccination disparities.

Safety and Immunogenicity Study of a Bivalent Vaccine for Combined Prophylaxis of COVID-19 and Influenza in Non-Human Primates

BACKGROUND

Influenza and SARS-CoV-2 viruses are two highly variable pathogens. We have developed a candidate bivalent live vaccine based on the strain of licensed A/Leningrad/17-based cold-adapted live attenuated influenza vaccine (LAIV) of H3N2 subtype, which expressed SARS-CoV-2 immunogenic T-cell epitopes. A cassette encoding fragments of S and N proteins of SARS-CoV-2 was inserted into the influenza NA gene using the P2A autocleavage site. In this study, we present the results of preclinical evaluation of the developed bivalent vaccine in a non-human primate model.

METHODS

Rhesus macaques (Macaca mulatta) (n = 3 per group) were immunized intranasally with 7.5 lg EID50 of the LAIV/CoV-2 bivalent vaccine, a control non-modified H3N2 LAIV or a placebo (chorioallantoic fluid) using a sprayer device, twice, with a 28-day interval. The blood samples were collected at days 0, 3, 28 and 35 for hematological and biochemical assessment. Safety was also assessed by monitoring body weight, body temperature and clinical signs of the disease. Immune responses to influenza virus were assessed both by determining serum antibody titers in hemagglutination inhibition assay, microneutralization assay and IgG ELISA. T-cell responses were measured both to influenza and SARS-CoV-2 antigens using ELISPOT and flow cytometry. Three weeks after the second immunization, animals were challenged with 105 PFU of Delta SARS-CoV-2. The body temperature, weight and challenge virus shedding were monitored for 5 days post-challenge. In addition, virus titers in various organs and histopathology were evaluated on day 6 after SARS-CoV-2 infection.

RESULTS

There was no toxic effect of the immunizations on the hematological and coagulation hemostasis of animals. No difference in the dynamics of the average weight and thermometry results were found between the groups of animals. Both LAIV and LAIV/CoV-2 variants poorly replicated in the upper respiratory tract of rhesus macaques. Nevertheless, despite this low level of virus shedding, influenza-specific serum IgG responses were detected in the group of monkeys immunized with the LAIV/CoV-2 bivalent but not in the LAIV group. Furthermore, T-cell responses to both influenza and SARS-CoV-2 viruses were detected in the LAIV/CoV-2 vaccine group only. The animals were generally resistant to SARS-CoV-2 challenge, with minimal virus shedding in the placebo and LAIV groups. Histopathological changes in vaccinated animals were decreased compared to the PBS group, suggesting a protective effect of the chimeric vaccine candidate.

CONCLUSIONS

The candidate bivalent vaccine was safe and immunogenic for non-human primates and warrants its further evaluation in clinical trials.

Combating the Co-Circulation of SARS-CoV-2 and Seasonal Influenza: Identifying Multi-Dimensional Factors Associated with the Uptake of Seasonal Influenza Vaccine among a Chinese National Sample

INTRODUCTION

The co-circulation of COVID-19 and seasonal influenza highlighted the importance of promoting influenza vaccination. However, the influenza vaccination rate among the Chinese population is low and requires further promotion. This study examined multi-dimensional factors, such as knowledge of seasonal influenza, health perceptions, cues to action, patient-provider relationships, and COVID-19 pandemic-related factors, in relation to the uptake of the seasonal influenza vaccine (SIV) among the Chinese population.

METHODS

A cross-sectional, self-administered online survey using a quota sampling method was conducted among Chinese adults 18 years and older between June and August 2022. Multivariate logistic regression was performed to explore factors associated with the 2021 SIV behavior.

RESULTS

A total of 3161 individuals from different regions of China were included in this study. The multivariate logistic regression demonstrated that perceived severity of influenza, perceived barriers to taking SIV, cues to action, a stable relationship with providers, worry about contracting COVID-19 in immunization settings, non-pharmaceutical interventions (NPIs), and awareness of the influenza vaccine in protecting against COVID-19 were significantly associated with the SIV uptake.

CONCLUSIONS

This study examined multi-dimensional factors that may influence SIV uptake. Health promotion programs should incorporate multi-dimensional factors, including personal and environmental factors, related to SIV promotion during the co-circulation period.

RSV Risk Profile in Hospitalized Adults and Comparison with Influenza and COVID-19 Controls in Valladolid, Spain, 2010-2022

INTRODUCTION

We aimed to describe the risk profile of respiratory syncytial virus (RSV) infections among adults ≥ 60 years in Valladolid from January 2010 to August 2022, and to compare them with influenza and COVID-19 controls.

METHODS

This was a retrospective cohort study of all laboratory-confirmed RSV infections identified in centralized microbiology database during a 12-year period. We analyzed risk factors for RSV hospitalization and severity (length of stay, intensive care unit admission, in-hospital death or readmission < 30 days) and compared severity between RSV patients vs. influenza and COVID-19 controls using multivariable logistic regression models.

RESULTS

We included 706 RSV patients (635 inpatients and 71 outpatients), and 598 influenza and 60 COVID-19 hospitalized controls with comparable sociodemographic profile. Among RSV patients, 96 (15%) had a subtype identified: 56% A, 42% B, and 2% A + B. Eighty-one percent of RSV patients had cardiovascular conditions, 65% endocrine/metabolic, 46% chronic lung, and 43% immunocompromising conditions. Thirty-six percent were coinfected (vs. 21% influenza and 20% COVID-19; p =  < .0001 and 0.01). Ninety-two percent had signs of lower respiratory infection (vs. 85% influenza and 72% COVID-19, p =  < .0001) and 27% cardiovascular signs (vs. 20% influenza and 8% COVID-19, p = 0.0031 and 0.0009). Laboratory parameters of anemia, inflammation, and hypoxemia were highest in RSV. Among RSV, being a previous smoker (adjusted OR 2.81 [95% CI 1.01, 7.82]), coinfection (4.34 [2.02, 9.34]), and having cardiovascular (3.79 [2.17, 6.62]), neurologic (2.20 [1.09, 4.46]), or chronic lung (1.93 [1.11, 3.38]) diseases were risks for hospitalization. Being resident in care institutions (1.68 [1.09, 2.61]) or having a coinfection (1.91[1.36, 2.69]) were risks for higher severity, while RSV subtype was not associated with severity. Whereas RSV and influenza patients did not show differences in severity, RSV patients had 68% (38-84%) lower odds of experiencing any severe outcome compared to COVID-19.

CONCLUSIONS

RSV especially affects those with comorbidities, coinfections, and living in care institutions. RSV vaccination could have an important public health impact in this population.

Association Between Influenza Vaccination and Acute Kidney Injury Among the Elderly: A Self-Controlled Case Series

BACKGROUND

Several cases of renal complications, including acute kidney injury (AKI), after influenza vaccination have been reported, but the association remains unproven. We evaluated the association between influenza vaccination and AKI occurrence among the Korean elderly in the 2018-2019 and 2019-2020 seasons.

METHODS

We used a large database combining vaccination registration data from the Korea Disease Control and Prevention Agency and claims data from the National Health Insurance Service. The study subjects were patients hospitalized with AKI for the first-time following vaccination among those who received one influenza vaccine in the 2018-2019 or 2019-2020 season. Only those aged 65 or older at the date of vaccination were included. We performed a self-controlled case series study, designating the risk period as 1 to 28 days post-vaccination and the observation period as each influenza season. The adjusted incidence rate ratio (aIRR) was calculated by adjusting for nephrotoxic drug use and influenza infection that may influence AKI occurrence using a conditional Poisson regression model.

RESULTS

A total of 16 713 and 16 272 AKI events were identified during the 2018-2019 and 2019-2020 seasons, respectively. The aIRR for AKI was 0.83 (95% confidence interval [CI] = 0.79-0.87) in the 2018-2019 season. The aIRR for the 2019-2020 influenza season was similar to the 2018-2019 season (aIRR = 0.86; 95% CI = 0.82-0.90).

CONCLUSIONS

Influenza vaccination is associated with a lower risk of AKI in the elderly over 65. This evidence supports the recommendation of annual influenza vaccination for the elderly. Further studies are needed to determine the biological mechanisms linking the influenza vaccine and AKI.

The role of influenza Hemagglutination-Inhibition antibody as a vaccine mediator in children

BACKGROUND

Influenza vaccination may protect through the humoral immune response, cellular immune response, or possibly both. Immunity after vaccination can be mediated through antibodies that may be detected by the rise of serum hemagglutination inhibition (HAI) titers. Our objective was to investigate the proportion of protection against influenza mediated through antibodies by measuring the rise of HAI titer (indirect effect) compared to that induced through other immune mechanisms (direct effect) for influenza A and B.

METHODS

We analysed data from a cluster randomized trial conducted during the 2008-2009 season in which Canadian Hutterite children were vaccinated against influenza. We used inverse probability weighting to calculate the indirect and direct effect of vaccination against influenza A/H3N2 and influenza B/Brisbane using HAI titres and overall vaccine efficacy.

RESULTS

We included data on 617 children from 46 Hutterite colonies, aged between 3 and 15 years who were vaccinated with either inactivated trivalent influenza vaccine or hepatitis A vaccine. Vaccine efficacy was 63 % for influenza A (H3N2) and 28 % for influenza B. The hazard ratio for protection against influenza A/H3N2 due to an indirect effect of vaccination was 0.96 (95 % confidence interval (CI) of 0.00 to 2.89) while for the direct effect it was 0.38 (95 % CI of 0.00 to 5.47). The hazard ratio for influenza B indirect effect was 0.75 (95 % CI of 0.07 to 1) and for the direct effect 0.96 (95 % CI of 0.00 to 12.02). In contrast, repeating the analysis using microneutralization in a subgroup of 488 children revealed that the protective effect for vaccination for A/H3N2 was entirely mediated by antibodies but only for 13 % for influenza B.

CONCLUSIONS

Although vaccination provided higher protective effectiveness against influenza A than B, most of the influenza A vaccine efficacy likely occurred through antibodies other than what could be detected by HAI titres. In contrast, for influenza B, while the HAI titres appeared to mediate most of the vaccine effectiveness, this was not confirmed by microneutralization analysis.

Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices - United States, 2024-25 Influenza Season

This report updates the 2023-24 recommendations of the Advisory Committee on Immunization Practices (ACIP) concerning the use of seasonal influenza vaccines in the United States (MMWR Recomm Rep 2022;72[No. RR-2]:1-24). Routine annual influenza vaccination is recommended for all persons aged ≥6 months who do not have contraindications. Trivalent inactivated influenza vaccines (IIV3s), trivalent recombinant influenza vaccine (RIV3), and trivalent live attenuated influenza vaccine (LAIV3) are expected to be available. All persons should receive an age-appropriate influenza vaccine (i.e., one approved for their age), with the exception that solid organ transplant recipients aged 18 through 64 years who are receiving immunosuppressive medication regimens may receive either high-dose inactivated influenza vaccine (HD-IIV3) or adjuvanted inactivated influenza vaccine (aIIV3) as acceptable options (without a preference over other age-appropriate IIV3s or RIV3). Except for vaccination for adults aged ≥65 years, ACIP makes no preferential recommendation for a specific vaccine when more than one licensed and recommended vaccine is available. ACIP recommends that adults aged ≥65 years preferentially receive any one of the following higher dose or adjuvanted influenza vaccines: trivalent high-dose inactivated influenza vaccine (HD-IIV3), trivalent recombinant influenza vaccine (RIV3), or trivalent adjuvanted inactivated influenza vaccine (aIIV3). If none of these three vaccines is available at an opportunity for vaccine administration, then any other age-appropriate influenza vaccine should be used.Primary updates to this report include the following two topics: the composition of 2024-25 U.S. seasonal influenza vaccines and updated recommendations for vaccination of adult solid organ transplant recipients. First, following a period of no confirmed detections of wild-type influenza B/Yamagata lineage viruses in global surveillance since March 2020, 2024-25 U.S. influenza vaccines will not include an influenza B/Yamagata component. All influenza vaccines available in the United States during the 2024-25 season will be trivalent vaccines containing hemagglutinin derived from 1) an influenza A/Victoria/4897/2022 (H1N1)pdm09-like virus (for egg-based vaccines) or an influenza A/Wisconsin/67/2022 (H1N1)pdm09-like virus (for cell culture-based and recombinant vaccines); 2) an influenza A/Thailand/8/2022 (H3N2)-like virus (for egg-based vaccines) or an influenza A/Massachusetts/18/2022 (H3N2)-like virus (for cell culture-based and recombinant vaccines); and 3) an influenza B/Austria/1359417/2021 (Victoria lineage)-like virus. Second, recommendations for vaccination of adult solid organ transplant recipients have been updated to include HD-IIV3 and aIIV3 as acceptable options for solid organ transplant recipients aged 18 through 64 years who are receiving immunosuppressive medication regimens (without a preference over other age-appropriate IIV3s or RIV3).This report focuses on recommendations for the use of vaccines for the prevention and control of seasonal influenza during the 2024-25 influenza season in the United States. A brief summary of the recommendations and a link to the most recent Background Document containing additional information are available at https://www.cdc.gov/acip-recs/hcp/vaccine-specific/flu.html?CDC_AAref_Val=https://www.cdc.gov/vaccines/hcp/acip-recs/vacc-specific/flu.html. These recommendations apply to U.S.-licensed influenza vaccines. Updates and other information are available from CDC's influenza website (https://www.cdc.gov/flu). Vaccination and health care providers should check this site periodically for additional information.

Risk of COVID-19 in Children throughout the Pandemic and the Role of Vaccination: A Narrative Review

At the beginning of the coronavirus disease 2019 (COVID-19) pandemic, persons ≥65 years of age and healthcare personnel represented the most vulnerable groups with respect to risk of infection, severe illness, and death. However, as the pandemic progressed, there was an increasingly detrimental effect on young children and adolescents. Severe disease and hospitalization increased over time in pediatric populations, and containment measures created substantial psychosocial, educational, and economic challenges for young people. Vaccination of children against COVID-19 has been shown to reduce severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections and severe outcomes in pediatric populations and may also help to prevent the spread of variants of concern and improve community immunity. This review discusses the burden of COVID-19 on children throughout the pandemic, the role of children in disease transmission, and the impact of COVID-19 vaccination.

Effectiveness of annual influenza campaigns and vaccination in reducing influenza burden in nursing homes of Canton Vaud in Switzerland

BACKGROUND

Influenza infections pose significant risks for nursing home (NH) residents. Our aim was to evaluate the impact of the cantonal influenza campaign, and influenza vaccination coverage of residents and healthcare workers (HCWs) on influenza burden in NHs in a context of enhanced infection prevention and control measures (IPC) during the SARS-CoV-2 pandemic.

METHODS

We extracted data from epidemic reports provided by our unit to NHs over two consecutive winter seasons (2021-22 and 2022-23) and used linear regression to assess the impact of resident and HCW vaccination coverage, and participation in the campaign, on residents' cumulative influenza incidence and mortality.

RESULTS

Thirty-six NHs reported 155 influenza cases and 21 deaths during the two winter seasons corresponding to 6.2% of infected residents and a case fatality ratio of 13.5%. Median vaccination coverage was 83% for residents, 25.8% for HCWs, while 87% of NHs participated in the campaign. Resident vaccination was significantly associated with a decrease in odds of death (odds ratio (OR) 0.96, 95% confidence interval (CI): 0.93-0.99). There was no significant effect of HCW vaccination coverage on resident infections and deaths. Campaign participation was associated with decreased odds of infection and death among residents (OR: 0.17, 95% CI: 0.06-0.47 and OR: 0.06, 95% CI: 0.02-0.17 respectively).

CONCLUSION

Our analysis suggests that in a context of reinforced IPC measures, influenza still represents a significant burden for NH residents. The most effective measures in decreasing resident influenza burden in NHs was participation in the cantonal influenza vaccination campaign and resident vaccination.

Assessment of Epidemiological Trend of Influenza-Like Illness in Italy from 2010/2011 to 2023/2024 Season: Key Points to Optimize Future Vaccination Strategies against Influenza

Seasonal influenza is an acute respiratory infectious disease due to influenza viruses, causing a relevant number of illnesses and deaths each year worldwide. Influenza is a preventable disease by vaccination. The aim of this study was to assess the epidemiology of seasonal influenza in Italy through the analysis of data from the epidemiological and virological RespiVirNet surveillance system for the season 2010/2011 to 2023/2024 to identify the epidemiological key points to plan the most appropriate vaccination strategies. The cumulative and maximum weekly incidence of influenza-like illness (ILI) and epidemic period (beginning, end, duration in weeks) were assessed in the pre-pandemic period (2010/2011-2019/2020) and they were compared to the pandemic and post-pandemic one. In all seasons, children reported the highest incidence values of ILI and longer epidemic periods in contrast with the older population. The epidemic seasons 2020/2021 and 2021/2022 had abnormal trends while in the last seasons 2022/2023 and 2023/2024 the epidemiological and virological trends of ILI were confirmed as reported in the pre-pandemic period but with high intensity. Influenza virus A was predominant: the H3N2 subtype circulated more than virus H1N1pdm09. In the few seasons when influenza virus B was the most frequent influenza agent, it co-circulated with influenza virus A. The monitoring of cases is the fundamental tool to better understand the epidemiology of influenza and to optimize future preventive strategies.

The Relationship between Immunogenicity and Reactogenicity of Seasonal Influenza Vaccine Using Different Delivery Methods

Vaccine immunogenicity and reactogenicity depend on recipient and vaccine characteristics. We hypothesized that healthy adults reporting higher reactogenicity from seasonal inactivated influenza vaccine (IIV) developed higher antibody titers compared with those reporting lower reactogenicity. We performed a secondary analysis of a randomized phase 1 trial of a trivalent IIV delivered by microneedle patch (MNP) or intramuscular (IM) injection. We created composite reactogenicity scores as exposure variables and used hemagglutination inhibition (HAI) titers as outcome variables. We used mixed-model analysis of variance to estimate geometric mean titers (GMTs) and titer fold change and modified Poisson generalized estimating equations to estimate risk ratios of seroprotection and seroconversion. Estimates of H3N2 GMTs were associated with the Systemic and Local scores among the IM group. Within the IM group, those with high reaction scores had lower baseline H3N2 GMTs and twice the titer fold change by day 28. Those with high Local scores had a greater probability of seroconversion. These results suggest that heightened reactogenicity to IM IIV is related to low baseline humoral immunity to an included antigen. Participants with greater reactogenicity developed greater titer fold change after 4 weeks, although the response magnitude was similar or lower compared with low-reactogenicity participants.

Evaluating Factors That Influence Influenza Vaccination Uptake among Pregnant People in a Medically Underserved Area in Washington State

INTRODUCTION

Despite substantial evidence demonstrating the effectiveness of influenza vaccines, only 38.6% of the adult United States population received an influenza vaccine during the 2023-2024 flu season. Vaccination rates are typically lower among U.S. minority groups, and in 2022, pregnant persons from U.S. minority racial and ethnic groups showed a decrease in influenza vaccine coverage.

METHODS

A survey was conducted with residents of Yakima County, Washington, which is home to one of the state's largest percentages of people who identify as Hispanic or Latino/a. The objective was to evaluate the uptake of influenza vaccine among pregnant persons. Surveys were sent to a random sample of 3000 residential mailing addresses. Of the 500 respondents, 244 (52.1%) reported that they had been pregnant, with those identifying as Hispanic or Latino/a constituting 23.8% of this total. Only 62 (26.2%) reported being immunized against influenza during pregnancy. Respondents who were immunized against influenza chose to be vaccinated to protect themselves from the flu (85.5%, n = 53); because a healthcare provider recommended getting vaccinated (85.5%, n = 53); to protect the baby from the flu (82.3%, n = 51); because it was available for free or low cost (62.9%, n = 39); and because vaccination was convenient (54.8%, n = 34). Qualitative evaluation identified that participants who were not vaccinated against influenza during pregnancy believed the vaccination was not needed, was not recommended by a healthcare provider, was difficult to access, they were against vaccination in general, or they were concerned about the safety and ingredients of the vaccine.

CONCLUSION

Barriers to vaccination identified in this study included vaccine distrust, lack of awareness, and concerns about vaccine efficacy and safety. Healthcare providers can help address these concerns by providing education and recommendations about the importance of influenza vaccination during pregnancy.

Increased efficacy of influenza virus vaccine candidate through display of recombinant neuraminidase on virus like particles

Vaccination against influenza virus can reduce the risk of influenza by 40% to 60%, they rely on the production of neutralizing antibodies specific to influenza hemagglutinin (HA) ignoring the neuraminidase (NA) as an important surface target. Vaccination with standardized NA concentration may offer broader and longer-lasting protection against influenza infection. In this regard, we aimed to compare the potency of a NA displayed on the surface of a VLP with a soluble NA. The baculovirus expression system (BEVS) and the novel virus-free Tnms42 insect cell line were used to express N2 NA on gag-based VLPs. To produce VLP immunogens with high levels of purity and concentration, a two-step chromatography purification process combined with ultracentrifugation was used. In a prime/boost vaccination scheme, mice vaccinated with 1 µg of the N2-VLPs were protected from mortality, while mice receiving the same dose of unadjuvanted NA in soluble form succumbed to the lethal infection. Moreover, NA inhibition assays and NA-ELISAs of pre-boost and pre-challenge sera confirm that the VLP preparation induced higher levels of NA-specific antibodies outperforming the soluble unadjuvanted NA.

Cost-Effectiveness of Adjuvanted Quadrivalent Influenza Vaccine for Adults over 65 in France

BACKGROUND

In France, influenza accounts for an average of over one million consultations with GPs, 20,000 hospitalizations, and 9000 deaths per year, particularly among the over-65s. This study evaluates the cost-effectiveness of the adjuvanted quadrivalent influenza vaccine (aQIV) compared to standard (SD-QIV) and high-dose (HD-QIV) quadrivalent influenza vaccines for individuals aged 65 and older in France.

METHODS

The age-structured SEIR transmission model, calibrated to simulate a mean influenza season, incorporates a contact matrix to estimate intergroup contact rates. Epidemiological, economic, and utility outcomes are evaluated. Vaccine effectiveness and costs are derived from literature and national insurance data. Quality of life adjustments for influenza attack rates and hospitalizations are applied. Deterministic and probabilistic analyses are also conducted.

RESULTS

Compared to SD-QIV, aQIV demonstrates substantial reductions in healthcare utilization and mortality, avoiding 89,485 GP consultations, 2144 hospitalizations, and preventing 1611 deaths. Despite an investment of EUR 110 million, aQIV yields a net saving of EUR 14 million in healthcare spending. Compared to HD-QIV, aQIV saves 62 million euros on vaccination costs. Cost-effectiveness analysis reveals an incremental cost-effectiveness ratio of EUR 7062 per QALY.

CONCLUSIONS

This study highlights the cost-effectiveness of aQIV versus SD-QIV and HD-QIV, preventing influenza cases, hospitalizations, and deaths.

Vaccines for the Elderly and Vaccination Programs in Europe and the United States

The share of the elderly population is growing worldwide as life expectancy increases. Immunosenescence and comorbidities increase infectious diseases' morbidity and mortality in older adults. Here, we aimed to summarize the latest findings on vaccines for the elderly against herpes zoster, influenza, respiratory syncytial virus (RSV), COVID-19, and pneumococcal disease and to examine vaccine recommendation differences for this age group in Europe and the United States. PubMed was searched using the keywords "elders" and "vaccine" alongside the disease/pathogen in question and paraphrased or synonymous terms. Vaccine recommendations were also sought in the European and US Centers for Disease Control and Prevention databases. Improved vaccines, tailored for the elderly, mainly by using novel adjuvants or by increasing antigen concentration, are now available. Significant differences exist between immunization policies, especially between European countries, in terms of the recipient's age, number of doses, vaccination schedule, and implementation (mandatory or recommended). Understanding the factors that influence the immune response to vaccination in the elderly may help to design vaccines that offer long-term protection for this vulnerable age group. A consensus-based strategy in Europe could help to fill the gaps in immunization policy in the elderly, particularly regarding vaccination against RSV and pneumococcus.

COVID-19 Vaccination Strategies in the Endemic Period: Lessons from Influenza

Coronavirus disease 2019 (COVID-19) is a highly contagious zoonotic respiratory disease with many similarities to influenza. Effective vaccines are available for both; however, rapid viral evolution and waning immunity make them virtually impossible to eradicate with vaccines. Thus, the practical goal of vaccination is to reduce the incidence of serious illnesses and death. Three years after the introduction of COVID-19 vaccines, the optimal vaccination strategy in the endemic period remains elusive, and health authorities worldwide have begun to adopt various approaches. Herein, we propose a COVID-19 vaccination strategy based on the data available until early 2024 and discuss aspects that require further clarification for better decision making. Drawing from comparisons between COVID-19 and influenza vaccination strategies, our proposed COVID-19 vaccination strategy prioritizes high-risk groups, emphasizes seasonal administration aligned with influenza vaccination campaigns, and advocates the co-administration with influenza vaccines to increase coverage.

Ipsilateral and contralateral coadministration of influenza and COVID-19 vaccines produce similar antibody responses

BACKGROUND

World Health Organisation (WHO) and USA Centers for Disease Control and Prevention (U.S. CDC) recommendations now allow simultaneous administration of COVID-19 and other vaccines. We compared antibody responses after coadministration of influenza and bivalent COVID-19 vaccines in the same (ipsilateral) arm vs. different (contralateral) arms.

METHODS

Pre- and post-vaccination serum samples from individuals in the Prospective Assessment of COVID-19 in a Community (PACC) cohort were used to conduct haemaglutination inhibition (HI) assays with the viruses in the 2022-2023 seasonal influenza vaccine and focus reduction neutralisation tests (FRNT) using a BA.5 SARS-CoV-2 virus. The effect of ipsilateral vs. contralateral vaccination on immune responses was inferred in a model that accounted for higher variance in vaccine responses at lower pre-vaccination titers.

FINDINGS

Ipsilateral vaccination did not cause higher influenza vaccine responses compared to contralateral vaccination. The response to SARS-CoV-2 was slightly increased in the ipsilateral group, but equivalence was not excluded.

INTERPRETATION

Coadministration of influenza and bivalent COVID-19 vaccines in the same arm or different arms did not strongly influence the antibody response to either vaccine.

FUNDING

This work was supported by the U.S. CDC (grant number: 75D30120C09259).

Cell-based influenza vaccines: An effective vaccine option for under 60-year-olds

Aim

Seasonal influenza poses a significant burden of disease, affecting not only older adults but also individuals under the age of 60. It carries a high economic burden, mainly driven by influenza-associated productivity losses in the working population. Conventional egg-based influenza vaccines may have reduced effectiveness due to antigen adaptation in eggs. In contrast, cell-based influenza vaccines are less likely to be affected by such antigen adaptation. This review aims to present real-world data (RWD) comparing the effectiveness of quadrivalent cell-based (QIVc) and egg-based (QIVe) influenza vaccines over three consecutive seasons.

Methods

A comprehensive review was conducted, analyzing RWD from retrospective cohort and case-control studies on the relative vaccine effectiveness (rVE) of QIVc versus QIVe during the 2017/18-2019/20 seasons.

Results

This study included six retrospective cohort studies and one case-control study, with a combined total of approximately 29 million participants. A cohort study involving people aged ≥4 years during the 2017/18 season showed a statistically significant rVE of QIVc compared to QIVe in preventing influenza-like illness, with a value of 36.2%. QIVc demonstrated statistically significant superiority over QIVe in preventing outpatient and inpatient medical encounters as observed in two cohort studies conducted during the 2018/19 and 2019/20 seasons. The rVE of QIVc compared to QIVe was found to be 7.6% in individuals aged ≥4 years and 9.5% in individuals aged ≥18 years. Three additional cohort studies conducted between 2017/18-2019/20 reported a statistically significant improvement in rVE (5.3-14.4%) of QIVc compared to QIVe in preventing influenza-related hospitalizations and emergency department visits due to influenza in individuals aged 4-64 years. In a case-control study across all three seasons, QIVc showed statistically significantly higher effectiveness compared to QIVe in preventing test-confirmed influenza, with rVEs of 10.0-14.8%.

Conclusions

RWD from the 2017/18-2019/20 seasons demonstrated that QIVc is more effective than QIVe in preventing influenza-related outcomes in individuals aged 4-64 years. Preferential use of cell-based influenza vaccines, as opposed to conventional egg-based vaccines, could reduce the burden of influenza-related symptoms on individuals and alleviate the economic impact on the German population under 60 years of age.

Characteristics and Outcomes of Pregnant Women Hospitalized With Laboratory-Confirmed Respiratory Syncytial Virus Before and During the COVID-19 Pandemic

Background

Respiratory syncytial virus (RSV) can cause severe disease among infants and older adults. Less is known about RSV among pregnant women.

Methods

To analyze hospitalizations with laboratory-confirmed RSV among women aged 18 to 49 years, we used data from the RSV Hospitalization Surveillance Network (RSV-NET), a multistate population-based surveillance system. Specifically, we compared characteristics and outcomes among (1) pregnant and nonpregnant women during the pre-COVID-19 pandemic period (2014-2018), (2) pregnant women with respiratory symptoms during the prepandemic and pandemic periods (2021-2023), and (3) pregnant women with and without respiratory symptoms in the pandemic period. Using multivariable logistic regression, we examined whether pregnancy was a risk factor for severe outcomes (intensive care unit admission or in-hospital death) among women aged 18 to 49 years who were hospitalized with RSV prepandemic.

Results

Prepandemic, 387 women aged 18 to 49 years were hospitalized with RSV. Of those, 350 (90.4%) had respiratory symptoms, among whom 33 (9.4%) were pregnant. Five (15.2%) pregnant women and 74 (23.3%) nonpregnant women were admitted to the intensive care unit; no pregnant women and 5 (1.6%) nonpregnant women died. Among 279 hospitalized pregnant women, 41 were identified prepandemic and 238 during the pandemic: 80.5% and 35.3% had respiratory symptoms, respectively (P < .001). Pregnant women were more likely to deliver during their RSV-associated hospitalization during the pandemic vs the prepandemic period (73.1% vs 43.9%, P < .001).

Conclusions

Few pregnant women had severe RSV disease, and pregnancy was not a risk factor for a severe outcome. More asymptomatic pregnant women were identified during the pandemic, likely due to changes in testing practices for RSV.

Web-based intervention for improving influenza vaccination in pregnant women: a cost-effectiveness analysis

A website with vaccine information and interactive social media was reported to improve maternal influenza vaccine uptake. This study aimed to evaluate cost-effectiveness of a web-based intervention on influenza vaccine uptake among pregnant women from the perspective of US healthcare providers. A one-year decision-analytic model estimated outcomes in a hypothetical cohort of pregnant women with: (1) website with vaccine information and interactive social media (intervention group), and (2) usual care (usual care group). Primary measures included influenza infection, influenza-related hospitalization, mortality, direct medical cost, and quality-adjusted life-year (QALY) loss. In base-case analysis, intervention group reduced cost (by USD28), infection (by 28 per 1,000 pregnant women), hospitalization (by 1.226 per 1,000 pregnant women), mortality (by 0.0036 per 1,000 pregnant women), and saved 0.000305 QALYs versus usual care group. Relative improvement of vaccine uptake by the intervention and number of pregnant women in the healthcare system were two influential factors identified in deterministic sensitivity analysis. The intervention was cost-effective in 99.5% of 10,000 Monte Carlo simulations (at willingness-to-pay threshold 50,000 USD/QALY). A website with vaccine information and interactive social media to promote influenza vaccination for pregnant women appears to reduce direct medical costs and gain QALYs from the perspective of US healthcare providers.

Interim Influenza Vaccine Effectiveness Against Laboratory-Confirmed Influenza - California, October 2023-January 2024

Surveillance data can provide rapid, within-season influenza vaccine effectiveness (VE) estimates to guide public health recommendations. Mandatory reporting of influenza vaccine administration to California's immunization information registry began January 1, 2023, and mandatory reporting of all influenza laboratory test results, including negative results, was instituted in California on June 15, 2023. These data, collected by the California Department of Public Health during October 1, 2023-January 31, 2024, were used to calculate interim influenza VE against laboratory-confirmed influenza by comparing the odds of vaccination among case-patients (persons who received a positive influenza laboratory test result) and control patients (those who received a negative influenza laboratory test result). VE was calculated as 1 - adjusted odds ratio using mixed-effects logistic regression, with age, race, and ethnicity as fixed effects and specimen collection week and county as random effects. Overall, during October 1, 2023-January 31, 2024, estimated VE was 45% among persons aged ≥6 months, 56% among children and adolescents aged 6 months-17 years, 48% among adults aged 18-49 years, 36% among those aged 50-64 years, and 30% among those aged ≥65 years. Consistent with some previous influenza seasons, influenza vaccination provided moderate protection against laboratory-confirmed influenza among infants, children, adolescents, and adults. All persons aged ≥6 months without a contraindication to vaccination should receive annual influenza vaccination to reduce influenza illness, severe influenza, and strain on health care resources. Influenza vaccination remains the best way to prevent influenza.