Effectiveness of the MF59-adjuvanted trivalent or quadrivalent seasonal influenza vaccine among adults 65 years of age or older, a systematic review and meta-analysis

The economic rationale for cell-based influenza vaccines in children and adults: A review of cost-effectiveness analyses

Seasonal influenza significantly affects both health and economic costs in children and adults. This narrative review summarizes published cost-effectiveness analyses (CEAs) of cell-based influenza vaccines in children and adults <65 years of age, critically assesses the assumptions and approaches used in these analyses, and considers the role of cell-based influenza vaccines for children and adults. CEAs from multiple countries demonstrated the cost-effectiveness of cell-based quadrivalent influenza vaccines (QIVc) compared with egg-based trivalent/quadrivalent influenza vaccines (TIVe/QIVe). CEA findings were consistent across models relying on different relative vaccine effectiveness (rVE) estimate inputs, with the rVE of QIVc versus QIVe ranging from 8.1% to 36.2% in favor of QIVc. Across multiple scenarios and types of analyses, QIVc was consistently cost-effective compared with QIVe, including in children and adults across different regions of the world.

Relative vaccine effectiveness of MF59-adjuvanted vs high-dose trivalent inactivated influenza vaccines for prevention of test-confirmed influenza hospitalizations during the 2017-2020 influenza seasons

OBJECTIVES

This study evaluated relative vaccine effectiveness (rVE) of MF59-adjuvanted trivalent inactivated influenza vaccine (aTIV) vs high-dose trivalent inactivated influenza vaccine (HD-TIV) for prevention of test-confirmed influenza emergency department visits and/or inpatient admissions ("ED/IP") and for IP admissions alone pooled across the 2017-2020 influenza seasons. Exploratory individual season analyses were also performed.

METHODS

This retrospective test-negative design study included United States (US) adults age ≥65 years vaccinated with aTIV or HD-TIV who presented to an ED or IP setting with acute respiratory or febrile illness during the 2017-2020 influenza seasons. Test-positive cases and test-negative controls were grouped by vaccine received. The rVE of aTIV vs HD-TIV was evaluated using a combination of inverse probability of treatment weighting and logistic regression to adjust for potential confounders.

RESULTS

Pooled analyses over the three seasons found no significant differences in the rVE of aTIV vs HD-TIV for prevention of test-confirmed influenza ED/IP (-2.5% [-19.6, 12.2]) visits and admissions or IP admissions alone (-1.6% [-22.5, 15.7]). The exploratory individual season analyses also showed no significant differences.

CONCLUSIONS

Evidence from the 2017-2020 influenza seasons indicates aTIV and HD-TIV are comparable for prevention of test-confirmed influenza ED/IP visits in US adults age ≥65 years.

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.

Comparative Effectiveness of mRNA-1273 and BNT162b2 COVID-19 Vaccines Among Older Adults: Systematic Literature Review and Meta-Analysis Using the GRADE Framework

INTRODUCTION

The mRNA vaccines mRNA-1273 and BNT162b2 demonstrated high efficacy against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in phase 3 clinical trials, including among older adults. To inform coronavirus disease 2019 (COVID-19) vaccine selection, this systematic literature review (SLR) and meta-analysis assessed the comparative effectiveness of mRNA-1273 versus BNT162b2 in older adults.

METHODS

We systematically searched for relevant studies reporting COVID-19 outcomes with mRNA vaccines in older adults aged ≥ 50 years by first cross-checking relevant published SLRs. Based on the cutoff date from a previous similar SLR, we then searched the WHO COVID-19 Research Database for relevant articles published between April 9, 2022, and June 2, 2023. Outcomes of interest were SARS-CoV-2 infection, symptomatic SARS-CoV-2 infection, severe SARS-CoV-2 infection, COVID-19-related hospitalization, and COVID-19-related death following ≥ 2 vaccine doses. Random effects meta-analysis models were used to pool risk ratios (RRs) across studies. Heterogeneity was evaluated using chi-square testing. Evidence certainty was assessed per GRADE framework.

RESULTS

Twenty-four non-randomized real-world studies reporting clinical outcomes with mRNA vaccines in individuals aged ≥ 50 years were included in the meta-analysis. Vaccination with mRNA-1273 was associated with significantly lower risk of SARS-CoV-2 infection (RR 0.72 [95% confidence interval (CI) 0.64‒0.80]), symptomatic SARS-CoV-2 infection (RR 0.72 [95% CI 0.62‒0.83]), severe SARS-CoV-2 infection (RR 0.67 [95% CI 0.57‒0.78]), and COVID-19-related hospitalization (RR 0.65 [95% CI 0.53‒0.79]) but not COVID-19-related death (RR 0.80 [95% CI 0.64‒1.00]) compared with BNT162b2. There was considerable heterogeneity between studies for all outcomes (I2 > 75%) except death (I2 = 0%). Multiple subgroup and sensitivity analyses excluding specific studies generally demonstrated consistent results. Certainty of evidence across outcomes was rated as low (type 3) or very low (type 4), reflecting the lack of randomized controlled trial data.

CONCLUSION

Meta-analysis of 24 observational studies demonstrated significantly lower risk of asymptomatic, symptomatic, and severe infections and hospitalizations with the mRNA-1273 versus BNT162b2 vaccine in older adults aged ≥ 50 years.

Estimates of Seasonal Influenza Burden That Could Be Averted by Improved Influenza Vaccines in the Australian Population Aged Under 65 Years, 2015-2019

BACKGROUND

The interpretation of relative vaccine effectiveness (rVE) of improved influenza vaccines is complex. Estimation of burden averted is useful to contextualise their potential impact across different seasons. For the population aged under 65 years in Australia, this study estimated the additional morbidity and mortality that could be averted using improved influenza vaccines.

METHODS

We used observed, season-specific (2015-2019) influenza notification and influenza-coded hospitalisation frequencies and published modelled estimates of influenza-associated hospitalisations and deaths that occurred under the prevailing influenza vaccination coverage scenario. After back-calculating to the estimated burden in the population without vaccination, we applied published standard influenza vaccine effectiveness and coverage estimates to calculate the burden potentially averted by standard and improved influenza vaccines. A plausible range of rVE values were used, assuming 50% coverage.

RESULTS

The percentage point difference in absolute vaccine effectiveness (VE) of an improved vaccine compared to a standard vaccine is directly proportional to its rVE and inversely proportional to the effectiveness of the standard vaccine. The incremental burden averted by an improved vaccine is a function of both its difference in absolute VE and the severity of the influenza season. Assuming an rVE of 15% with 50% coverage, the improved vaccine was estimated to additionally avert 1517 to 12,641 influenza notifications, 287 to 1311 influenza-coded hospitalisations and 9 to 33 modelled all-cause influenza deaths per year compared to the standard vaccine.

CONCLUSIONS

Improved vaccines can have substantial clinical and population impact, particularly when the effectiveness of standard vaccines is low, and burden is high.

Immunogenicity of Enhanced Influenza Vaccines Against Mismatched Influenza Strains in Older Adults: A Review of Randomized Controlled Trials

Antigenic drift is a major driver of viral evolution and a primary reason why influenza vaccines must be reformulated annually. Mismatch between vaccine and circulating viral strains negatively affects vaccine effectiveness and often contributes to higher rates of influenza-related hospitalizations and deaths, particularly in years dominated by A(H3N2). Several countries recommend enhanced influenza vaccines for older adults, who are at the highest risk of severe influenza complications and mortality. The immunogenicity of enhanced vaccines against heterologous A(H3N2) strains has been examined in nine studies to date. In six studies, an enhanced, licensed MF59-adjuvanted trivalent inactivated influenza vaccine (aIIV3) consistently increased heterologous antibody titers relative to standard influenza vaccine, with evidence of a broad heterologous immune response across multiple genetic clades. In one study, licensed high-dose trivalent inactivated influenza vaccine (HD-IIV3) also induced higher heterologous antibody titers than standard influenza vaccine. In a study comparing a higher dose licensed quadrivalent recombinant influenza vaccine (RIV4) with HD-IIV3 and aIIV3, no significant differences in antibody titers against a heterologous strain were observed, although seroconversion rates were higher with RIV4 versus comparators. With the unmet medical need for improved influenza vaccines, the paucity of studies especially with enhanced vaccines covering mismatched strains highlights a need for further investigation of cross-protection in older adults.

Relative Effectiveness of the MF59®-Adjuvanted Influenza Vaccine Versus High-Dose and Non-Adjuvanted Influenza Vaccines in Preventing Cardiorespiratory Hospitalizations During the 2019-2020 US Influenza Season

BACKGROUND

Adults ≥ 65 years of age have suboptimal influenza vaccination responses compared to younger adults due to age-related immunosenescence. Two vaccines were specifically developed to enhance protection: MF59-adjuvanted trivalent influenza vaccine (aIIV3) and high-dose egg-based trivalent influenza vaccine (HD-IIV3e).

METHODS

In a retrospective cohort study conducted using US electronic medical records linked to claims data during the 2019-2020 influenza season, we compared the relative vaccine effectiveness (rVE) of aIIV3 with HD-IIV3e and a standard-dose non-adjuvanted egg-based quadrivalent inactivated influenza vaccine (IIV4e) for the prevention of cardiorespiratory hospitalizations, including influenza hospitalizations. We evaluated outcomes in the "any" diagnosis position and the "admitting" position on the claim. A doubly robust methodology using inverse probability of treatment weighting and logistic regression was used to adjust for covariate imbalance. rVE was calculated as 100 * (1 - ORadjusted).

RESULTS

The study included 4,299,594 adults ≥ 65 years of age who received aIIV3, HD-IIV3e, or IIV4e. Overall, aIIV3 was associated with lower proportions of cardiorespiratory hospitalizations with diagnoses in any position compared to HD-IIV3e (rVE = 3.9% [95% CI, 2.7-5.0]) or IIV4e (9.0% [95% CI, 7.7-10.4]). Specifically, aIIV3 was more effective compared with HD-IIV3e and IIV4e in preventing influenza hospitalizations (HD-IIV3e: 9.7% [95% CI, 1.9-17.0]; IIV4e: 25.3% [95% CI, 17.7-32.2]). Consistent trends were observed for admitting diagnoses.

CONCLUSION

Relative to both HD-IIV3e and IIV4e, aIIV3 provided improved protection from cardiorespiratory or influenza hospitalizations.

Engineered dityrosine-bonding of the RSV prefusion F protein imparts stability and potency advantages

Viral fusion proteins facilitate cellular infection by fusing viral and cellular membranes, which involves dramatic transitions from their pre- to postfusion conformations. These proteins are among the most protective viral immunogens, but they are metastable which often makes them intractable as subunit vaccine targets. Adapting a natural enzymatic reaction, we harness the structural rigidity that targeted dityrosine crosslinks impart to covalently stabilize fusion proteins in their native conformations. We show that the prefusion conformation of respiratory syncytial virus fusion protein can be stabilized with two engineered dityrosine crosslinks (DT-preF), markedly improving its stability and shelf-life. Furthermore, it has 11X greater potency as compared with the DS-Cav1 stabilized prefusion F protein in immunogenicity studies and overcomes immunosenescence in mice with simply a high-dose formulation on alum.

Covid-19 and influenza vaccine effectiveness against associated hospital admission and death among individuals over 65 years in Norway: A population-based cohort study, 3 October 2022 to 20 June 2023

BACKGROUND

Co-circulation of SARS-CoV-2 and influenza virus can lead to double epidemics and increased pressure on health systems. To evaluate the effect of both vaccines, we estimated the adjusted vaccine effectiveness (aVE) of influenza and Covid-19 vaccines against related severe disease in the elderly population in Norway during the 2022/2023 season.

METHODS

In this population-based cohort study, we included data from the Emergency preparedness register for Covid-19 (Beredt C19) on all individuals ≥ 65 years living in Norway between 3 October 2022 and 20 June 2023. Using Cox-proportional hazard models, we estimated aVE of both influenza and Covid-19 vaccines (bivalent BA.1 and BA.4-5) against associated hospitalisation and death. Vaccine status was included as a time-varying covariate and all models were adjusted for potential confounders, including the other vaccine.

RESULTS

We identified 2,437 influenza-associated hospitalisations and 178 deaths, alongside 5,824 Covid-19-associated hospitalisations and 621 deaths. The aVE was highest in the first three months after receiving either vaccine. Against influenza-associated hospitalisation the aVE was 34 % (26 %-42 %) among 65-79-year-olds and 40 % (30 %-48 %) among ≥ 80-year-olds, and 6.6 % (-64 %-47 %) and 37 % (0.5 %-61 %) against influenza-associated death, respectively. The aVE against Covid-19-associated hospitalisation was 65 % (61 %-69 %) among 65-79-year-olds and 55 % (49 %-60 %) among ≥ 80-year-olds (compared to having received the vaccine ≥ 180 days ago). Similarly, the aVE against Covid-19-associated death was 68 % (48 %-80 %) and 78 % (65 %-86 %), respectively. For Covid-19 we show a reduction in aVE with time since dose.

CONCLUSION

Covid-19 and influenza vaccines reduced the risk of severe disease in the same high-risk population. Ensuring high uptake of both vaccines could thus limit the overall health care burden.

Mapping and ranking outcomes for the evaluation of seasonal influenza vaccine efficacy and effectiveness: a delphi study

BACKGROUND

Protection provided by seasonal influenza vaccination (SIV) may be measured against numerous outcomes, and their heterogeneity may hamper decision-making. The aim of this study was to explore outcomes used for estimation of SIV efficacy/effectiveness (VE) and obtain expert consensus on their importance.

RESEARCH DESIGN AND METHODS

An umbrella review was first conducted to collect and map outcomes considered in systematic reviews of SIV VE. A Delphi study was then performed to reach expert convergence on the importance of single outcomes, measured on a 9-point Likert scale, in principal target groups, namely children, working-age adults, older adults, subjects with co-morbidities and pregnant women.

RESULTS

The literature review identified 489 outcomes. Following data reduction, 20 outcomes were selected for the Delphi process. After two Delphi rounds and a final consensus meeting, convergence was reached. All 20 outcomes were judged to be important or critically important. More severe outcomes, such as influenza-related hospital encounters and mortality with or without laboratory confirmation, were generally top-ranked across all target groups (median scores ≥8 out of 9).

CONCLUSIONS

Rather than focusing on laboratory-confirmed infection per se, experimental and observational VE studies should include more severe influenza-related outcomes because they are expected to exercise a greater impact on decision-making.

Inactivated recombinant influenza vaccine: the promising direction for the next generation of influenza vaccine

INTRODUCTION

Vaccination is the most effective method to control the prevalence of seasonal influenza and the most widely used influenza vaccine is the inactivated influenza vaccine (IIV). Each season, the influenza vaccine must be updated to be most effective against current circulating variants. Therefore, developing a universal influenza vaccine (UIV) that can elicit both broad and durable protection is of the utmost importance.

AREA COVERED

This review summarizes and compares the available influenza vaccines in the market and inactivation methods used for manufacturing IIVs. Then, we discuss the latest progress of the UIV development in the IIV format and the challenges to address for moving these vaccine candidates to clinical trials and commercialization. The literature search was based on the Centers for Disease Control and Prevention (CDC) and the PubMed databases.

EXPERT OPINION

The unmet need for UIV is the primary aim of developing the next generation of influenza vaccines. The IIV has high antigenicity and a refined manufacturing process compared to most other formats. Developing the UIV in IIV format is a promising direction with advanced biomolecular technologies and next-generation adjuvant. It also inspires the development of universal vaccines for other infectious diseases.

Vaccines against extraintestinal pathogenic Escherichia coli (ExPEC): progress and challenges

The emergence of antimicrobial resistance (AMR) is a principal global health crisis projected to cause 10 million deaths annually worldwide by 2050. While the Gram-negative bacteria Escherichia coli is commonly found as a commensal microbe in the human gut, some strains are dangerously pathogenic, contributing to the highest AMR-associated mortality. Strains of E. coli that can translocate from the gastrointestinal tract to distal sites, called extraintestinal E. coli (ExPEC), are particularly problematic and predominantly afflict women, the elderly, and immunocompromised populations. Despite nearly 40 years of clinical trials, there is still no vaccine against ExPEC. One reason for this is the remarkable diversity in the ExPEC pangenome across pathotypes, clades, and strains, with hundreds of genes associated with pathogenesis including toxins, adhesins, and nutrient acquisition systems. Further, ExPEC is intimately associated with human mucosal surfaces and has evolved creative strategies to avoid the immune system. This review summarizes previous and ongoing preclinical and clinical ExPEC vaccine research efforts to help identify key gaps in knowledge and remaining challenges.

A clinical and economic assessment of adjuvanted trivalent versus standard egg-derived quadrivalent influenza vaccines among older adults in the United States during the 2018-19 and 2019-20 influenza seasons

BACKGROUND

Clinical evidence supports use of enhanced influenza vaccines in older adults. Few economic outcome studies have compared adjuvanted trivalent inactivated (aIIV3) and standard egg-derived quadrivalent inactivated influenza vaccines (IIV4e).

RESEARCH DESIGN AND METHODS

A retrospective cohort study was conducted leveraging deidentified US hospital data linked to claims data during the 2018-19 and 2019-20 influenza seasons. Relative vaccine effectiveness (rVE) was compared in adults aged ≥ 65 years receiving aIIV3 or IIV4e using inverse probability of treatment weighting (IPTW) and Poisson regression. An economic assessment quantified potential real-world cost savings.

RESULTS

The study included 715,807 aIIV3 and 320,991 IIV4e recipients in the 2018-19 and 844,169 aIIV3 and 306,270 IIV4e recipients in the 2019-20 influenza seasons. aIIV3 was significantly more effective than IIV4e in preventing cardiorespiratory disease (2018-19 rVE = 6.2%; and 2019-20 rVE = 6.0%) and respiratory disease (2018-19 rVE = 8.9%; and 2019-20 rVE = 10.1%). During the 2018-19 influenza season cardiorespiratory hospitalization cost savings for the aIIV3 population were $392 M, and $221 M for the 2019-20 season. Respiratory hospitalization cost savings for the aIIV3 population were $145 M and $97 M, respectively.

CONCLUSIONS

Our findings suggest that aIIV3 provides clinical and economic advantages versus IIV4e in the elderly.

Systematic review of influenza vaccine effectiveness against laboratory-confirmed influenza among older adults living in aged care facilities

We estimated the effectiveness of influenza vaccines in preventing laboratory-confirmed influenza among older adults in aged care. Electronic database searches were conducted using search terms, and studies were selected as per the selection criteria. Fourteen studies were included for final review. The studies exhibited considerable variation in reported vaccine effectiveness (VE) across different seasons. Among the observational studies, VE ranged from 7.2% to 89.8% against laboratory-confirmed influenza across different vaccines. Randomized clinical trials demonstrated a 17% reduction in infection rates with the adjuvanted trivalent vaccine. The limitations include the small number of included studies conducted in different countries or regions, varied seasons, variations in diagnostic testing methods, a focus on the A/H3N2 strain, and few studies available on the effectiveness of enhanced influenza vaccines in aged care settings. Despite challenges associated with achieving optimal protection, the studies showed the benefits of influenza vaccination in the elderly residents.

Evaluating risk of bias using ROBINS-I tool in nonrandomized studies of adjuvanted influenza vaccine

Seasonal variation in influenza vaccine effectiveness (VE) makes real-world evidence (RWE) useful in supplementing the clinical-evidence base from randomized clinical trials. Adjuvanted inactivated influenza vaccine (aIIV) VE has been evaluated in multiple nonrandomized RWE studies. A systematic literature review of RWE studies evaluating the absolute or relative VE of aIIV was conducted. Identified studies were assessed by evaluators for risk of bias (RoB) by means of the ROBINS-I (Reduction of Bias In Non-randomized Studies of Interventions) tool to inform evidence-based medicine deliberations. Differences in evaluator assessments were resolved by consensus. The literature review yielded 14 follow-up studies, seven test-negative case-control (TNCC) studies, five traditional case-control studies, and one cluster-randomized clinical trial. Most follow-up studies and three TNCC studies were judged at low RoB. Issues increasing RoB included inadequate control of confounding, selection of controls, and reliance on recall of vaccination. The concerns identified in any of the designs could be mitigated with straightforward revisions to design or implementation. 17 of 27 nonrandomized studies of adjuvanted influenza-vaccine effectiveness, some from each of four study designs, were judged at low risk of material bias. These studies merit credence in assessing aIIV effectiveness relative to other influenza vaccines.

Rollout of the 2022/2023 Seasonal Influenza Vaccination and Correlates of the Use of Enhanced Vaccines among Italian Adults

In Italy, several types of seasonal influenza vaccines (SIVs) are available for older adults, but for the 2022/2023 season there were no guidelines on their specific use. This cross-sectional study assessed the frequency and determinants of the use of enhanced (adjuvanted and high-dose) SIVs in Italian older adults, as compared to standard-dose non-adjuvanted formulations. Of 1702 vaccines administered to a representative outpatient sample of adults aged ≥ 60 years and residing in Genoa, 69.5% were enhanced SIVs. Older age (adjusted odds ratio (aOR) for each 1-year increase 1.10; p < 0.001), and the presence of cardiovascular disease (aOR 1.40; p = 0.011) and diabetes (aOR 1.62; p = 0.005) were associated with the use of enhanced vaccines. Compared with the adjuvanted SIV, subjects immunized with the high-dose vaccine were older (aOR for each 1-year increase 1.05; p < 0.001) and had higher prevalence of respiratory diseases (aOR 1.85; p = 0.052). Moreover, usage of the enhanced SIVs was driven by the period of immunization campaign, place of vaccination and physician. Despite their superior immunogenicity and effectiveness, the adoption of enhanced SIVs in Italy is suboptimal, and should be increased. Enhanced formulations are mostly used in the oldest, and in subjects with some co-morbidities.

Cost-effectiveness for high dose quadrivalent versus the adjuvanted quadrivalent influenza vaccine in the Italian older adult population

Objectives

To assess the cost-effectiveness of switching from adjuvanted quadrivalent vaccine (aQIV) to high-dose quadrivalent influenza vaccine (HD-QIV) in those aged ≥65 years from the Italian National Health Service perspective.

Methods

We developed a decision tree model over a 1-year time-horizon to assess influenza-related costs and health outcomes. Two hospitalization approaches were considered: "hospitalization conditional on developing influenza" and "hospitalization possibly related to Influenza." The first approach considered only hospitalizations with influenza ICD-9-CM diagnosis codes. The second included hospitalizations for cardiorespiratory events possibly related to influenza to better capture the "hidden burden". Since comparative efficacy of high-dose quadrivalent influenza vaccine versus adjuvanted quadrivalent vaccine was lacking, we assumed relative efficacy versus a common comparator, standard-dose influenza quadrivalent vaccines (SD-QIV). We assumed the relative efficacy of HD-QIV vs. SD-QIV was 24.2 and 18.2% for the first and second hospitalization approaches, respectively, based on published information. Due to lack of comparative efficacy data for aQIV vs. SD-QIV, we assumed three different scenarios: 0, 6, and 12% relative efficacy in scenarios 1, 2, and 3, respectively.

Results

For the first hospitalization approach, HD-QIV was a cost-effective alternative to aQIV in all scenarios at a willingness-to-pay threshold of €30,000 per Quality Adjusted Life Years. The incremental cost-effectiveness ratios across the scenarios were €7,301, €9,805, and €14,733, respectively, much lower than the willingness-to-pay per Quality Adjusted Life Years threshold. For the second hospitalization approach, HD-QIV was a dominant alternative to aQIV across all scenarios. The robustness of the results was confirmed in one-way and probabilistic sensitivity analyses.

Conclusion

Switching to HD-QIV from aQIV for the older adult in Italy would improve health-related outcomes, and would be cost-effective or cost saving.

Baseline immune states (BIS) associated with vaccine responsiveness and factors that shape the BIS

Vaccines are among the greatest inventions in medicine, leading to the elimination or control of numerous diseases, including smallpox, polio, measles, rubella, and, most recently, COVID-19. Yet, the effectiveness of vaccines varies among individuals. In fact, while some recipients mount a robust response to vaccination that protects them from the disease, others fail to respond. Multiple clinical and epidemiological factors contribute to this heterogeneity in responsiveness. Systems immunology studies fueled by advances in single-cell biology have been instrumental in uncovering pre-vaccination immune cell types and genomic features (i.e., the baseline immune state, BIS) that have been associated with vaccine responsiveness. Here, we review clinical factors that shape the BIS, and the characteristics of the BIS associated with responsiveness to frequently studied vaccines (i.e., influenza, COVID-19, bacterial pneumonia, malaria). Finally, we discuss potential strategies to enhance vaccine responsiveness in high-risk groups, focusing specifically on older adults.

Vaccine Effectiveness of non-adjuvanted and adjuvanted trivalent inactivated influenza vaccines in the prevention of influenza-related hospitalization in older adults: A pooled analysis from the Serious Outcomes Surveillance (SOS) Network of the Canadian Immunization Research Network (CIRN)

BACKGROUND

Influenza vaccines prevent influenza-related morbidity and mortality; however, suboptimal vaccine effectiveness (VE) of non-adjuvanted trivalent inactivated influenza vaccine (naTIV) or quadrivalent formulations in older adults prompted the use of enhanced products such as adjuvanted TIV (aTIV). Here, the VE of aTIV is compared to naTIV for preventing influenza-associated hospitalization among older adults.

METHODS

A test-negative design study was used with pooled data from the 2012 to 2015 influenza seasons. An inverse probability of treatment (IPT)-weighted logistic regression estimated the Odds Ratio (OR) for laboratory-confirmed influenza-associated hospitalization. VE was calculated as (1-OR)*100% with accompanying 95% confidence intervals (CI).

RESULTS

Of 7,101 adults aged ≥ 65, 3,364 received naTIV and 526 received aTIV. The overall VE against influenza hospitalization was 45.9% (95% CI: 40.2%-51.1%) for naTIV and 53.5% (42.8%-62.3%) for aTIV. No statistically significant differences in VE were found between aTIV and naTIV by age group or influenza season, though a trend favoring aTIV over naTIV was noted. Frailty may have impacted VE in aTIV recipients compared to those receiving naTIV, according to an exploratory analysis; VE adjusted by frailty was 59.1% (49.6%-66.8%) for aTIV and 44.8% (39.1%-50.0%) for naTIV. The overall relative VE of aTIV to naTIV against laboratory-confirmed influenza hospital admission was 25% (OR 0.75; 0.61-0.92), demonstrating statistically significant benefit favoring aTIV.

CONCLUSIONS

Adjusting for frailty, aTIV showed statistically significantly better protection than naTIV against influenza-associated hospitalizations in older adults. In future studies, it is important to consider frailty as a significant confounder of VE.

Immunogenicity and Safety of MF59-Adjuvanted Quadrivalent Influenza Vaccine Compared with a Nonadjuvanted, Quadrivalent Influenza Vaccine in Adults 50-64 Years of Age

Adults aged 50-64 years have a high incidence of symptomatic influenza associated with substantial disease and economic burden each year. We conducted a randomized, controlled trial to compare the immunogenicity and safety of an adjuvanted quadrivalent inactivated influenza vaccine (aIIV4; n = 1027) with a nonadjuvanted standard dose IIV4 (n = 1017) in this population. Immunogenicity was evaluated on Days 22, 181, and 271. On Day 22, upper limits (UL) of 95% confidence intervals (CI) for geometric mean titer (GMT) ratios (IIV4/aIIV4) were <1.5 and 95% CI ULs for the difference in seroconversion rate (SCR IIV4 - aIIV4) were <10% for all four vaccine strains, meeting primary endpoint noninferiority criteria. Protocol-defined superiority criteria (95% CI ULs < 1.0) were also met for A(H1N1) and A(H3N2). Immune responses following aIIV4 vaccination were more pronounced in persons with medical comorbidities and those not recently vaccinated against influenza. Safety data were consistent with previous studies of MF59 adjuvanted seasonal and pandemic influenza vaccines. These findings support the immunological benefit of aIIV4 for persons aged 50-64 years, especially those with comorbidities.

The Impact of Adjuvanted Influenza Vaccine on Disease Severity in the US: A Stochastic Model

Influenza can exacerbate underlying medical conditions. In this study, we modelled the potential impact of an egg-based quadrivalent influenza vaccine (QIVe) or adjuvanted QIV (aQIV) on hospitalizations and mortality from influenza-related cardiovascular disease (CVD), respiratory, and other complications in adults ≥65 years of age in the US with underlying chronic conditions. We used a stochastic decision-tree model, with 1000 simulations varying input across predicted ranges. Due to the variable nature of influenza across seasons and differences in published estimates for input parameters, data are presented as 95% confidence intervals. Compared with no vaccination, use of aQIV would prevent 135,450-564,360 hospitalizations and 1612-29,226 deaths across outcomes evaluated. Overall, aQIV prevented 1071-18,388 more hospitalizations and 85-1944 more deaths than QIVe. By routine seasonal vaccination against influenza, a substantial number of severe influenza-associated complications and deaths, caused by direct influenza symptoms or by exacerbation of chronic conditions, can be prevented in high-risk adults ≥65 years of age in the US.

Contributions of cost-effectiveness analyses (CEA) to influenza vaccination policy for older adults in Europe

This review describes the importance of economic evaluations and real-world evidence (RWE) for the assessment of enhanced influenza vaccines for older adults in Europe. Individuals ≥65 years of age are at increased risk of severe influenza outcomes and many countries in Europe recommend enhanced vaccines for this population to mitigate immunosenescence. Some National Immunization Technical Advisory Groups (NITAGs) may preferentially recommend a specific enhanced vaccine, necessitating comparative economic evaluation and estimation of relative vaccine effectiveness between enhanced vaccine options in the absence of direct head-to-head efficacy data. Distinct approaches to economic modeling and cost-effectiveness analysis (CEA) guide national vaccination policies in Europe, including how underlying data, such as RWE, are used in these models. RWE is an important evidence source for input into CEA models based on disease factors (e.g., antigenic shift and seasonal variation) and practical factors (e.g., limitations of performing multiple randomized clinical trials to capture seasonal variation; the need to obtain relevant patient-oriented, real-world endpoints, such as hospitalizations). CEA is considered crucial to vaccine assessment among certain countries in Europe, but further harmonization of economic evaluations, including the use of RWE, across NITAGs in Europe may be of benefit, alongside standardized approaches for vaccine appraisal. In the future, more countries may use RWE as an input in CEA models to support NITAG recommendations for enhanced influenza vaccines in older populations, especially considering the value of RWE for the assessment of influenza epidemiology and vaccine effectiveness as stated by the World Health Organization, and the availability of a broad RWE base for certain enhanced vaccines.

Immunogenicity and safety of inactivated quadrivalent influenza vaccine compared with the trivalent vaccine for influenza infection: an overview of systematic reviews

BACKGROUND

Influenza infection is a highly preventable transmissible viral disease associated with mild upper respiratory symptoms and more severe conditions such as lethal pneumonia. Studies have shown that a broader spectrum influenza vaccine could reduce influenza's burden of disease in low- and middle-income countries. A considerable number of systematic reviews reported that quadrivalent influenza vaccines are considered more effective compared to trivalent vaccines, hence, there is a need for an overview in order to synthesize the current evidence pertaining to the comparison between quadrivalent and trivalent inactivated influenza vaccines.

OBJECTIVE

The aim was to summarize the evidence from systematic reviews that investigated the immunogenicity and safety of the Influenza's inactivated quadrivalent vaccine (QIV) compared to the trivalent vaccine (TIV), in the general population.

METHODS

We searched articles up to December 2022 at: Web of Science, EMBASE, MEDLINE, Cochrane Library, and SCOPUS. The search strategy was conducted following the PICO model. We included systematic reviews comparing the primary outcomes of immunogenicity (seroprotection rate and seroconversion rate) and adverse events using risk ratios. The AMSTAR 2 and ROBIS were used for quality assessments, and GRADE was used for evidence certainty assessments.

FINDINGS

We included five systematic reviews, totalling 47,740 participants. The Quadrivalent Inactivated Influenza Vaccine (QIV) exhibited enhanced immunogenicity in the context of B-lineage mismatch when compared to the Trivalent Inactivated Influenza Vaccine (TIV). While the safety profile of QIV was found to be comparable to that of TIV, the QIV showed a higher incidence of solicited local pain among children and adolescents, as well as an increased frequency of local adverse events within the adult population.

CONCLUSION

Our findings suggest that the QIV provides a superior immunogenicity response compared to the TIV in all age groups evaluated, especially when a lineage mismatch occurred. The safety of QIV was considered similar to the TIV, with no serious or systemic solicited or unsolicited adverse events; tough pain at the injection site was greater for QIV. We recommend caution owing to the high risk of bias in the selection process and no protocol registration.

Additional Burden Averted in the United States From Use of MF59-Adjuvanted Seasonal Influenza Vaccine Compared With Standard Seasonal Influenza Vaccine Among Adults ≥65 Years

Background

The MF59-adjuvanted trivalent inactivated influenza vaccine (aIIV3) is designed to overcome immunosenescence and enhance vaccine responses in older adults. We expanded on the Centers for Disease Control and Prevention (CDC) modeling method to estimate the number of additional influenza-related outcomes averted with aIIV3 versus generic quadrivalent inactivated influenza vaccine (IIV4) in adults ≥65 years over 3 influenza seasons (2017-2018 to 2019-2020) in the United States.

Methods

A static compartmental model was developed based on an existing CDC model with 2 previously recommended calculation methods that increased the accuracy of the model in providing estimates of burden averted. Model inputs included vaccine effectiveness, vaccine coverage, population counts, and disease burden estimates. Additional burden averted (symptomatic cases, outpatient visits, hospitalizations, intensive care unit [ICU] admissions, and deaths) was expressed as total incremental cases averted between the vaccines. Sensitivity analyses tested the resilience of the model results to uncertainties in model inputs.

Results

The model estimated that vaccination with aIIV3 versus IIV4 would avert 2.24 times as many symptomatic cases, outpatient visits, hospitalizations, ICU stays, and deaths during 2017-2018; the burden averted in 2018-2019 and 2019-2020 with aIIV3 would be 3.44 and 1.72 times that averted with IIV4, respectively. Disease burden estimates and relative vaccine effectiveness of aIIV3 had the greatest impact on model estimates.

Conclusions

Over 3 influenza seasons, the model estimated that aIIV3 was more effective than IIV4 in averting influenza-related outcomes, preventing 1.72 to 3.44 times as many influenza illnesses with proportionate decreases in related healthcare use and complications.

Influenza vaccine effectiveness in preventing hospital encounters for laboratory-confirmed infection among Italian adults, 2022/23 season

The effectiveness of seasonal influenza vaccination (SIV) varies from year to year. Interim estimates of vaccine effectiveness (VE) in outpatient settings have suggested that the 2022/23 northern hemisphere SIV was 54 % effective. The main goal of this study was to measure the 2022/23 SIV VE among Italian adults in a hospital setting. The study adopted a retrospective test-negative case-control design and was conducted in a large tertiary hospital (Genoa, Italy) between October 2022 and April 2023. Adult (≥18 years) patients accessing the hospital's Emergency Department for symptoms ascribable to an acute respiratory infection, for which a reverse-transcription real-time polymerase chain reaction test for the detection of influenza virus was prescribed, were potentially eligible. Of 33,692 referrals assessed, 487 patients were included in the study. A total of 13 % of patients were positive for influenza, most of which (63 %) belonged to the A(H3N2) subtype. SIV VE was 57 % (95 % CI: 11-81 %), 53 % (95 % CI: 2-80 %) and 38 % (95 % CI: -34-74 %) against any influenza, influenza A and A(H3N2), respectively. Although no cases caused by A(H1N1)pdm09 and B strains were observed among vaccinated individuals, VE estimates against the latter were imprecise, owing to their low detection rates. In conclusion, the 2022/23 SIV was moderately effective against hospital encounters for laboratory-confirmed influenza.

Cost-effectiveness of the adjuvanted quadrivalent influenza vaccine in the elderly Belgian population

BACKGROUND

Between 2015 and 2019, when 62% of Belgian adults aged ≥ 65 years were vaccinated with standard quadrivalent influenza vaccines, influenza caused an average of 3,905 hospitalizations and 347 premature deaths per year in older adults. The objective of the present analysis was to estimate the cost-effectiveness of the adjuvanted quadrivalent influenza vaccine (aQIV) compared to the standard (SD-QIV) and high-dose (HD-QIV) vaccines in elderly Belgians.

RESEARCH DESIGN AND METHODS

The analysis was based on a static cost-effectiveness model that captured the evolution of patients infected with influenza and was customized with available national data.

RESULTS

Vaccinating adults aged ≥ 65 years with aQIV instead of SD-QIV would decrease the number of hospitalizations by 530 and the number of deaths by 66 in the 2023-2024 influenza season. aQIV was cost-effective compared to SD-QIV with an incremental cost of €15,227/quality-adjusted life year (QALY). aQIV is cost-saving when compared to HD-QIV in the subgroup of institutionalized elderly adults who were granted reimbursement for this vaccine.

CONCLUSION

In a health care system striving to improve the prevention of infectious diseases, a cost-effective vaccine such as aQIV is a key asset to reduce the number of influenza-related hospitalizations and premature deaths in older adults.

PLAIN LANGUAGE SUMMARY

A flu vaccine containing a unique immune boosting additive reduces medical spending by reducing flu hospitalizations and early deaths in the elderly.

Polyfunctional antibodies: a path towards precision vaccines for vulnerable populations

Vaccine efficacy determined within the controlled environment of a clinical trial is usually substantially greater than real-world vaccine effectiveness. Typically, this results from reduced protection of immunologically vulnerable populations, such as children, elderly individuals and people with chronic comorbidities. Consequently, these high-risk groups are frequently recommended tailored immunisation schedules to boost responses. In addition, diverse groups of healthy adults may also be variably protected by the same vaccine regimen. Current population-based vaccination strategies that consider basic clinical parameters offer a glimpse into what may be achievable if more nuanced aspects of the immune response are considered in vaccine design. To date, vaccine development has been largely empirical. However, next-generation approaches require more rational strategies. We foresee a generation of precision vaccines that consider the mechanistic basis of vaccine response variations associated with both immunogenetic and baseline health differences. Recent efforts have highlighted the importance of balanced and diverse extra-neutralising antibody functions for vaccine-induced protection. However, in immunologically vulnerable populations, significant modulation of polyfunctional antibody responses that mediate both neutralisation and effector functions has been observed. Here, we review the current understanding of key genetic and inflammatory modulators of antibody polyfunctionality that affect vaccination outcomes and consider how this knowledge may be harnessed to tailor vaccine design for improved public health.

Real-World Evidence in Cost-Effectiveness Analysis of Enhanced Influenza Vaccines in Adults ≥ 65 Years of Age: Literature Review and Expert Opinion

Influenza vaccination can benefit most populations, including adults ≥ 65 years of age, who are at greater risk of influenza-related complications. In many countries, enhanced vaccines, such as adjuvanted, high-dose, and recombinant trivalent/quadrivalent influenza vaccines (aTIV/aQIV, HD-TIV/HD-QIV, and QIVr, respectively), are recommended in older populations to provide higher immunogenicity and increased relative vaccine efficacy/effectiveness (rVE) than standard-dose vaccines. This review explores how efficacy and effectiveness data from randomized controlled trials and real-world evidence (RWE) are used in economic evaluations. Findings from published cost-effectiveness analyses (CEA) on enhanced influenza vaccines for older adults are summarized, and the assumptions and approaches used in these CEA are assessed alongside discussion of the importance of RWE in CEA. Results from many CEA showed that adjuvanted and high-dose enhanced vaccines were cost-effective compared with standard vaccines, and that differences in rVE estimates and acquisition price may drive differences in cost-effectiveness estimates between enhanced vaccines. Overall, RWE and CEA provide clinical and economic rationale for enhanced vaccine use in people ≥ 65 years of age, an at-risk population with substantial burden of disease. Countries that consider RWE when making vaccine recommendations have preferentially recommended aTIV/aQIV, as well as HD-TIV/HD-QIV and QIVr, to protect older individuals.

Impact of aging on immunity in the context of COVID-19, HIV, and tuberculosis

Knowledge of aging biology needs to be expanded due to the continuously growing number of elderly people worldwide. Aging induces changes that affect all systems of the body. The risk of cardiovascular disease and cancer increases with age. In particular, the age-induced adaptation of the immune system causes a greater susceptibility to infections and contributes to the inability to control pathogen growth and immune-mediated tissue damage. Since the impact of aging on immune function, is still to be fully elucidated, this review addresses some of the recent understanding of age-related changes affecting key components of immunity. The emphasis is on immunosenescence and inflammaging that are impacted by common infectious diseases that are characterized by a high mortality, and includes COVID-19, HIV and tuberculosis.

Cost-Effectiveness of the Use of Adjuvanted Quadrivalent Seasonal Influenza Vaccine in Older Adults in Ireland

BACKGROUND

Enhanced vaccines (e.g., containing adjuvants) have shown increased immunogenicity and effectiveness in older adults, who often respond sub-optimally to conventional influenza vaccines. In this study, we evaluated the cost-effectiveness of an inactivated, seasonal, MF59-adjuvanted quadrivalent influenza vaccine (aQIV) for use in adults ≥ 65 years in Ireland.

METHODS

A published dynamic influenza model incorporating social contact, population immunity, and epidemiological data was used to assess the cost-effectiveness of aQIV in adults ≥ 65 years of age compared with a non-adjuvanted QIV. Sensitivity analysis was performed for influenza incidence, relative vaccine effectiveness, excess mortality, and the impact on bed occupancy from co-circulating influenza and COVID-19.

RESULTS

The use of aQIV resulted in discounted incremental cost-effectiveness ratios (ICERs) of EUR 2420/quality-adjusted life years (QALYs) and EUR 12,970/QALY from societal and payer perspectives, respectively, both of which are below the cost-effectiveness threshold of EUR 45,000/QALY. Sensitivity analysis showed that aQIV was effective in most scenarios, except when relative vaccine effectiveness compared to QIV was below 3%, and resulted in a modest reduction in excess bed occupancy.

CONCLUSION

The use of aQIV for adults ≥ 65 years old in Ireland was shown to be highly cost-effective from both payer and societal perspectives.

Cost-Effectiveness of Vaccination of Older Adults with an MF59®-Adjuvanted Quadrivalent Influenza Vaccine Compared to Standard-Dose and High-Dose Vaccines in Denmark, Norway, and Sweden

Individuals aged 65 years and above are at increased risk of complications and death from influenza compared with any other age group. Enhanced vaccines, as the MF59®-adjuvanted quadrivalent influenza vaccine (aQIV) and the high-dose quadrivalent influenza vaccine (HD-QIV), provide increased protection for older adults in comparison to the traditional standard-dose quadrivalent influenza vaccines (SD-QIV). This study aimed to assess the cost-effectiveness of aQIV compared to SD-QIV and HD-QIV in Denmark, Norway, and Sweden for adults aged ≥65 years. A static decision tree model was used to evaluate costs and outcomes of different vaccination strategies from healthcare payer and societal perspectives. This model projects that compared to SD-QIV, vaccination with aQIV could prevent a combined total of 18,772 symptomatic influenza infections, 925 hospitalizations, and 161 deaths in one influenza season across the three countries. From a healthcare payer perspective, the incremental costs per quality adjusted life year (QALY) gained with aQIV versus SD-QIV were EUR 10,170/QALY in Denmark, EUR 12,515/QALY in Norway, and EUR 9894/QALY in Sweden. The aQIV was cost saving compared with HD-QIV. This study found that introducing aQIV to the entire population aged ≥65 years may contribute to reducing the disease and economic burden associated with influenza in these countries.

Vaccine-Preventable Diseases in Older Adults

Older adults are at an increased risk of vaccine-preventable diseases partly because of physiologic changes in the immune and other body systems related to age and/or accumulating comorbidities that increase the vulnerability to infections and decrease the response to vaccines. Strategies to improve the response to vaccines include using a higher antigenic dose (such as in the high-dose inactivated influenza vaccines) as well as adding adjuvants (such as MF59 in the adjuvanted inactivated influenza vaccine).

An Economic Comparison in the Elderly of Adjuvanted Quadrivalent Influenza Vaccine with Recombinant Quadrivalent Influenza Vaccine in Spain

Influenza infections impose a high burden of morbidity and mortality among older adults, at great cost to individuals and society. Enhanced influenza vaccines, which contain either an immune adjuvant or higher than normal doses of influenza virus antigens, are recommended for older adults. We used a health economics model to evaluate the cost effectiveness in Spain of a recently licensed recombinant quadrivalent influenza vaccine (QIVr), which contains three times the standard dose of influenza virus hemagglutinin but no neuraminidase, compared with an MF59-adjuvanted quadrivalent influenza vaccine (aQIV). Based on current tender prices in Spain and a conservative assumption that QIVr is 10.7% relatively more effective than aQIV, the incremental cost-effectiveness ratio (ICER) for QIVr was EUR 101,612.41 per quality-adjusted life year (QALY) gained. To meet the Spanish willingness-to-pay threshold of EUR 25,000 per QALY gained, QIVr would need to be 34.1% relatively more effective than aQIV. In a probabilistic sensitivity analysis conducted to confirm the robustness of the analysis, 99.7% of simulations for QIVr were higher than the willingness-to-pay curve. These findings suggest that QIVr is not currently a cost-effective influenza vaccine option relative to aQIV for older persons living in Spain.

Impact of General Practitioner Education on Acceptance of an Adjuvanted Seasonal Influenza Vaccine among Older Adults in England

Seasonal vaccination against influenza and in-pandemic COVID-19 vaccination are top public health priorities; vaccines are the primary means of reducing infections and also controlling pressures on health systems. During the 2018-2019 influenza season, we conducted a study of the knowledge, attitudes, and behaviours of 159 general practitioners (GPs) and 189 patients aged ≥65 years in England using a combination of qualitative and quantitative approaches to document beliefs about seasonal influenza and seasonal influenza vaccine. GPs were surveyed before and after a continuing medical education (CME) module on influenza disease and vaccination with an adjuvanted trivalent influenza vaccine (aTIV) designed for patients aged ≥65 years, and patients were surveyed before and after a routine visit with a GP who participated in the CME portion of the study. The CME course was associated with significantly increased GP confidence in their ability to address patients' questions and concerns about influenza disease and vaccination (p < 0.001). Patients reported significantly increased confidence in the effectiveness and safety of aTIV after meeting their GP. Overall, 82.2% of the study population were vaccinated against influenza (including 137 patients vaccinated during the GP visit and 15 patients who had been previously vaccinated), a rate higher than the English national average vaccine uptake of 72.0% that season. These findings support the value of GP-patient interactions to foster vaccine acceptance.

Estimating the Impact of Influenza Vaccination on Acute and ICU Hospital Bed Usage in an Influenza Season under Endemic COVID-19 in the US

In 2021–2022, influenza vaccine coverage in the US dropped below pre-COVID-19 pandemic levels. Cocirculation of COVID-19 and influenza could place a substantial burden on hospital utilization in future seasons, particularly given the reduced exposure to influenza during the pandemic. We used a dynamic susceptible-exposed-infected-recovered model to simulate influenza transmission with varying influenza vaccine coverage against a background of COVID-19 circulation, in order to estimate acute and ICU hospital bed occupancy for both diseases. We evaluated two vaccine scenarios: egg-based quadrivalent influenza vaccine (QIVe) for all age groups or cell-based QIV (QIVc) for 0.5–64 year-olds with adjuvanted QIV (aQIV) for ≥65 year-olds. ICU bed availability was more limiting than general hospital bed availability, with a vaccine coverage of ≥70% required to avoid negatively impacting ICU bed availability in a high-incidence influenza season. The timing of disease peaks was a key factor together with vaccine coverage, with a difference of ≥50 days needed between peak influenza and COVID-19 bed usage together with 65% influenza vaccine coverage to avoid negative impacts. QIVc + aQIV resulted in lower bed occupancy which, while not substantial, may be critical in very high hospital resource usage situations. In a situation with co-circulating influenza and COVID-19, proactive vaccination planning could help to avert overwhelming healthcare systems in upcoming influenza seasons.

Relative effectiveness of the adjuvanted vs non-adjuvanted seasonal influenza vaccines against severe laboratory-confirmed influenza among hospitalized Italian older adults

OBJECTIVES

In this study, we aimed to investigate the relative vaccine effectiveness (rVE) of the MF59-adjuvanted trivalent (aTIV) and non-adjuvanted quadrivalent (QIVe) egg-based standard-dose vaccines against severe laboratory-confirmed influenza.

METHODS

This test-negative case-control study was conducted in a hospital setting during four recent Italian influenza seasons (from 2018/19 to 2021/22). The clinical outcome was severe acute respiratory infection (SARI) with laboratory confirmation diagnosed among subjects aged ≥65 years. rVE of aTIV versus QIVe was estimated through propensity score matching followed by logistic regression.

RESULTS

The influenza virus circulated to a significant extent only during the 2018/19 and 2019/20 seasons. The final population included 512 vaccinated older adults, of which 83 were cases and 429 were test-negative controls. aTIV and QIVe users differed substantially from the point of view of several baseline characteristics. The propensity score adjusted rVE of aTIV vs QIVe was 59.2% (95% CI: 14.6%, 80.5%), 54.7% (95% CI: -28.7%, 84.0%) and 56.9% (95% CI: -7.8%, 82.8%) against any influenza, A(H1N1)pdm09 and A(H3N2), respectively.

CONCLUSION

aTIV was more effective than QIVe in preventing laboratory-confirmed SARI. The benefits of aTIV may be obscured by confounding indication.

Relative Vaccine Effectiveness of Adjuvanted Trivalent Influenza Vaccine over Three Consecutive Influenza Seasons in the United States

Traditional influenza vaccines may be less immunogenic in adults ≥65 years of age due to immunosenescence. Two influenza vaccines—MF59®-adjuvanted trivalent inactivated influenza vaccine (aIIV3) and high-dose influenza vaccine (HD-IIV3)—were developed to overcome this problem. We summarize estimates of the relative vaccine effectiveness (rVE) of aIIV3 vs. HD-IIV3 and aIIV3 vs. standard, egg-based quadrivalent influenza vaccines (IIV4e) during the 2017–2018, 2018–2019, and 2019–2020 US influenza seasons using the same underlying electronic medical record and linked claims dataset for all three seasons. The primary outcome was influenza-related medical encounters (IRMEs), defined by diagnostic codes specific to influenza (ICD J09*-J11*). rVE was estimated using propensity score methods adjusting for demographics and health status. rVE estimates demonstrated consistent benefit for aIIV3 over IIV4e in the overall and at-risk populations. Relative to HD-IIV3, aIIV3 provided improved benefit in the overall study population and comparable benefit in the at-risk population across each season.

The Cost-Effectiveness of Vaccination of Older Adults with an MF59-Adjuvanted Quadrivalent Influenza Vaccine Compared to Other Available Quadrivalent Vaccines in Germany

Enhanced quadrivalent influenza vaccines that include an adjuvant (aQIV) or a high dose of antigen (QIV-HD), which stimulate a stronger immune response in older adults than the standard vaccine (QIVe), are now approved. The objective of this research is to compare available vaccines and determine the cost-effectiveness of immunizing persons aged 65 years and above with aQIV compared to QIVe and QIV-HD in Germany. A compartmental transmission model calibrated to outpatient visits for influenza in Germany was used to predict the number of medically attended infections using the three vaccines. The rates of hospitalizations, deaths, and other economic consequences were estimated with a decision tree using German data where available. Based on meta-analysis, the rVE of −2.5% to 8.9% for aQIV versus QIV-HD, the vaccines are similar clinically, but aQIV is cost saving compared to QIV-HD (unit cost of EUR 40.55). All results were most sensitive to changes in vaccine effectiveness. aQIV may be cost-effective compared to QIVe depending on the willingness to pay for additional benefits in Germany. As aQIV and QIV-HD are similar in terms of effectiveness, aQIV is cost saving compared to QIV-HD at current unit prices.

A Comparative Analysis of Influenza-Associated Disease Burden with Different Influenza Vaccination Strategies for the Elderly Population in South Korea

Influenza affects all age groups, but the risk of hospitalization and death due to influenza is strongly age-related and is at its highest among the elderly aged 65 years and older. The objective of this study is to compare the differences in influenza-associated disease burden under three different influenza vaccination strategies—the standard-dose quadrivalent influenza vaccine (QIV), high-dose QIV (HD-QIV), and MF59^®-adjuvanted QIV (aQIV)—for the elderly population aged 65 years and older in South Korea. A one-year decision-tree model was developed to compare influenza disease burdens. The input data for the model were obtained from published literature reviews and surveillance data from the Korea Disease Control and Prevention Agency (KDCA). The analysis indicated that aQIV is more effective than QIV, preventing 35,390 influenza cases, 1602 influenza-associated complications, 709 influenza-associated hospitalizations, and 145 influenza-associated deaths annually. Additionally, aQIV, when compared to HD-QIV, also reduced the influenza-associated burden of disease, preventing 7247 influenza cases, 328 influenza-associated complications, 145 influenza-associated hospitalizations, and 30 influenza-associated deaths annually. Switching the vaccination strategy from QIV to aQIV is predicted to reduce the influenza-associated disease burden for the elderly in South Korea. The public health gains from aQIV and HD-QIV are expected to be comparable. Future studies comparing the effectiveness of the vaccines will further inform future vaccination strategies for the elderly in South Korea.

Characteristics and methodological standards across systematic reviews with Meta-analysis of efficacy and/or effectiveness of influenza vaccines: an overview of reviews

BACKGROUND

While systematic reviews (SR) generally suggest that vaccination is an effective way to prevent influenza infection, it is not clear if these conclusions are based on high quality SR methods. As such, we systematically identified, critically appraised, and summarised the characteristics and adherence to methodological standards in SRs with meta-analysis of efficacy/effectiveness of influenza vaccines.

METHODS

We searched MEDLINE, Embase, Scopus, CINAHL, Global Health, and CDSR for English-language SR publications up to July 11, 2022. We summarised the characteristics, adherence to methodological standards and SR quality (AMSTAR 2).

RESULTS

From 11,193 retrieved citations, we included 48 publications (47 SRs). Seventy-five percent were of a critically low quality, 19% of a low quality, 2% of a moderate quality, and 4% of a high quality. Thirteen percent were industry-funded, about 13% co-authored by industry employee(s), and 4% commissioned by an organisation or authority. Only 45% percent reported protocol registration, 6% reported collaboration with a knowledge synthesis librarian/information specialist, and 60% utilised a reporting checklist (e.g. PRISMA).

CONCLUSIONS AND RELEVANCE

SRs with meta-analysis of efficacy/effectiveness of influenza vaccines are mostly of critically low quality and even the more recent reviews did not follow current best SR practices. These findings are significant in view of the controversies that surround influenza vaccines, and the use of SRs in informed decision-making. However, the findings do not justify curtailment or cessation of influenza vaccine use as vaccines continue to offer substantial net public health benefit.HighlightsWe systematically identified, critically appraised, and summarised the characteristics and adherence to methodological standards in 47 systematic reviews with meta-analysis of efficacy/effectiveness of influenza vaccines.13% of the reviews were industry-funded.About 13% of the reviews were co-authored by industry employee(s).4% of the reviews were commissioned by an organisation/authority.45% of the reviews reported protocol registration.6% of the reviews reported collaborating with a knowledge synthesis librarian/information specialist to prepare the search strategy.60% of the reviews reported using the PRISMA (or similar) checklist.75% of the reviews were judged to be of critically low quality; 19% of low quality; 2% of moderate quality; 4% of high quality.

An Economic Evaluation of the Adjuvanted Quadrivalent Influenza Vaccine Compared with Standard-Dose Quadrivalent Influenza Vaccine in the Spanish Older Adult Population

Standard-dose quadrivalent influenza vaccines (QIV) are designed to provide protection against all four influenza strains. Adjuvanted QIV (aQIV), indicated for individuals aged 65+ years, combines MF59^® adjuvant (an oil-in-water emulsion of squalene oil) with a standard dose of antigen, and is designed to produce stronger and longer immune response, especially in the elderly where immunosenescence reduces vaccine effectiveness. This study evaluated the cost-effectiveness of aQIV vs. egg-based standard-dose QIV (QIVe) in the elderly population, from the payer and societal perspective in Spain. A dynamic transmission model, which accounts for herd protection, was used to predict the number of medically attended infections in Spain. A decision tree structure was used to forecast influenza-related costs and benefits. Influenza-related probabilities of outpatient visit, hospitalization, work absenteeism, mortality, and associated utilities and costs were extracted from Spanish and European published literature. Relative vaccine effectiveness (rVE) was sourced from two different meta-analyses: the first meta-analysis was informed by laboratory-confirmed influenza studies only, resulting in a rVE = 34.6% (CI95% 2-66%) in favor of aQIV; the second meta-analysis included real world evidence influenza-related medical encounters outcomes, resulting in a rVE = 13.9% (CI95% 4.2-23.5%) in benefit of aQIV. All costs were expressed in 2021 euros. Results indicate that replacing QIVe with aQIV in the Spanish elderly population would prevent on average 43,664 influenza complicated cases, 1111 hospitalizations, and 569 deaths (with a rVE = 34.6%) or 19,104 influenza complicated cases, 486 hospitalizations, and 252 deaths (with a rVE = 13.9%). When the rVE of aQIV vs. QIVe is 34.6%, the incremental cost per quality adjusted life years (QALY) gained was €2240 from the payer; from the societal perspective, aQIV was cost saving compared with QIVe. If the rVE was 13.9%, the incremental cost per QALY was €6694 and €3936 from the payer and societal perspective, respectively. Sensitivity analyses validated the robustness of these findings. Results indicate that replacing QIVe with aQIV in the Spanish elderly population is a cost-effective strategy for the Spanish healthcare system.

Adjuvanted versus non-adjuvanted standard-dose influenza vaccines in preventing all-cause hospitalizations in the elderly: a cohort study with nested case-control analyses over 18 influenza seasons

BACKGROUND

The higher effectiveness of adjuvanted trivalent influenza vaccine (aTIV) versus non-adjuvanted (na) formulations in preventing all-cause hospitalization has been demonstrated for a single influenza season and in institutionalized elderly only. This study evaluated the relative vaccine effectiveness for aTIV vs. non-adjuvanted trivalent (naTIV) and/or quadrivalent (naQIV) influenza vaccines in preventing all-cause hospitalizations across 18 influenza seasons in primary care.

RESEARCH DESIGN AND METHODS

Using Health Search Database, a nested case-control analysis was conducted in a cohort of older adults being vaccinated with aTIV or naTIV/naQIV. Conditional logistic regression was adopted to estimate the odds ratio (OR) of all-cause hospitalizations occurred during the epidemic period.

RESULTS

Of 58,252 patients vaccinated with aTIV and naTIV/naQIV for the first time, 2,504 cases of all-cause hospitalization (3.46 per 1,000 person-weeks) during the 18 influenza seasons were identified. Compared with naTIV/naQIV, aTIV was associated with a 12% reduced the odds of all-cause hospitalizations (OR 0.88; 95% CI: 0.80-0.98).

CONCLUSIONS

In an 18-season cohort of older adults, aTIV reduced the risk of all-cause hospitalizations when compared with naTIV/naQIV. Our findings confirm additional benefits for adjuvanted influenza vaccines in older adults.

Modelling the Economic Impact of lnfluenza Vaccine Programs with the Cell-Based Quadrivalent Influenza Vaccine and Adjuvanted Trivalent Influenza Vaccine in Canada

In Canada, approximately 12,000 people annually are hospitalized with influenza. While vaccination is the most effective method for reducing the burden of seasonal influenza, the propagation of vaccine virus strains in eggs can result in egg adaption, resulting in reduced antigenic similarity to circulating strains and thus lower vaccine effectiveness (VE). Cell-based propagation methods avoid these alterations and therefore may be more effective than egg-propagation vaccines. We evaluated three different scenarios: (1) egg-based quadrivalent influenza vaccine (QIVe) for individuals <65 years and adjuvanted trivalent influenza vaccine (aTIV) for ≥65 years; (2) QIVe (<65 years) and high-dose QIV (HD −; QIV; ≥65 years); and (3) cell-based derived QIV (QIVc; <65 years) and aTIV (≥65 years) compared with a baseline scenario of QIVe for all age groups. Modelling was performed using a dynamic age-structured SEIR model, which assessed each strain individually using data from the 2012−2019 seasons. Probabilistic sensitivity analysis assessed the robustness of the results with respect to variation in absolute VE, relative VE, number of egg-adapted seasons, and economic parameters. QIVe + aTIV was cost-saving compared with the baseline scenario (QIVe for all), and QIVe + HD − QIV was not cost-effective in the majority of simulations, reflecting the high acquisition cost of HD − QIV. Overall, while the incremental benefits may vary by influenza season, QIVc + aTIV resulted in the greatest reductions in cases, hospitalizations, and mortality, and was cost-effective (ICER < CAD 50,000) in all simulations.

Comparative effectiveness of adjuvanted versus high-dose seasonal influenza vaccines for older adults: A systematic review and meta-analysis

OBJECTIVES

MF59-adjuvanted standard-dose and non-adjuvanted high-dose seasonal influenza vaccines have been developed to protect older adults at high risk of severe complications. The aim of this study was to summarize the available evidence on the comparative efficacy/effectiveness of these two vaccines.

METHODS

A systematic literature review (CRD42022313021) of experimental and observational studies was conducted according to the PRISMA guidelines. When possible, the extracted effect sizes were pooled in random-effects meta-analyses.

RESULTS

Ten studies were identified. Of these, no head-to-head randomized controlled trials were identified. All available studies had retrospective cohort design and large sample sizes, were conducted in the United States between 2016/17 and 2019/20 seasons and were at moderate risk of bias. Relative effectiveness estimates were limited to non-laboratory-confirmed clinical endpoints, such as medical encounters including hospitalizations. While most pooled relative effectiveness estimates were close to null, few statistically significant pooled effect sizes were small in magnitude, moved in opposite directions and depended on both the study sponsor and specificity of influenza-related outcomes.

CONCLUSIONS

At current, MF59-adjuvanted standard-dose and non-adjuvanted high-dose vaccines appear to have similar effectiveness in preventing seasonal influenza in older adults and no conclusive recommendations on the preference of one vaccine over another could be drawn.

Review of Analyses Estimating Relative Vaccine Effectiveness of Cell-Based Quadrivalent Influenza Vaccine in Three Consecutive US Influenza Seasons

The adaptation of influenza seed viruses in egg culture can result in a variable antigenic vaccine match each season. The cell-based quadrivalent inactivated influenza vaccine (IIV4c) contains viruses grown in mammalian cell lines rather than eggs. IIV4c is not subject to egg-adaptive changes and therefore may offer improved protection relative to egg-based vaccines, depending on the degree of match with circulating influenza viruses. We summarize the relative vaccine effectiveness (rVE) of IIV4c versus egg-based quadrivalent influenza vaccines (IIV4e) to prevent influenza-related medical encounters (IRMEs) from three retrospective observational cohort studies conducted during the 2017–2018, 2018–2019, and 2019–2020 US influenza seasons using the same underlying electronic medical record dataset for all three seasons—with the addition of linked medical claims for the latter two seasons. We identified IRMEs using diagnostic codes specific to influenza disease (ICD J09*-J11*) from the records of over 10 million people. We estimated rVE using propensity score methods adjusting for age, sex, race, ethnicity, geographic location, week of vaccination, and health status. Subgroup analyses included specific age groups. IIV4c consistently had higher relative effectiveness than IIV4e across all seasons assessed, which were characterized by different dominant circulating strains and variable antigenic drift or egg adaptation.

Importance and value of adjuvanted influenza vaccine in the care of older adults from a European perspective - A systematic review of recently published literature on real-world data

BACKGROUND

There is an urgent need for improved influenza vaccines especially for older adults due to the presence of immunosenescence. It is therefore highly relevant to compare enhanced influenza vaccines with traditional influenza vaccines with respect to their effectiveness.

OBJECTIVE

To compare vaccine efficacy and effectiveness of adjuvanted influenza vaccines (aTIV/aQIV) vs. non-adjuvanted standard-dose (TIV/QIV) and high-dose (TIV-HD/QIV-HD) influenza vaccines regarding influenza-related outcomes in older adults, complementing findings from the European Centre for Disease Prevention and Control (ECDC)'s systematic review of enhanced seasonal influenza vaccines from February 2020.

METHODS

A systematic literature search was conducted in Embase and MEDLINE to identify randomised controlled trials, observational studies and systematic reviews, published since ECDC's systematic review (between 7 February 2020 and 6 September 2021). Included studies were appraised with either the Cochrane Risk of Bias tool, ROBINS-I or AMSTAR 2.

RESULTS

Eleven analyses from nine real-world evidence (RWE) studies comprising ∼53 million participants and assessing the relative vaccine effectiveness (rVE) of aTIV vs. TIV, QIV and/or TIV-HD in adults aged ≥65 years over the 2006/07-2008/09 and 2011/12-2019/20 influenza seasons were identified. Nine analyses found that aTIV was significantly more effective than TIV and QIV in reducing influenza-related outcomes by clinical setting and suspected influenza outbreaks (rVE ranging from 7.5% to 25.6% for aTIV vs. TIV and 7.1% to 36.3% for aTIV vs. QIV). Seven analyses found similar effectiveness of aTIV vs. TIV-HD in reducing influenza-related medical encounters, inpatient stays and hospitalisations/emergency room visits. In three analyses, aTIV was significantly more effective than TIV-HD in reducing influenza-related medical encounters and office visits (rVE ranging from 6.6% to 16.6%). Risk of bias of identified studies was moderate to high.

CONCLUSIONS

Our study suggests that both adjuvanted and high-dose vaccines are effective alternatives for vaccination programmes in older adults and preferable over conventional standard-dose vaccines.