Effectiveness of MF59-adjuvanted seasonal influenza vaccine in the elderly: A systematic review and meta-analysis

Effectiveness of influenza vaccine among the population in Chongqing, China, 2018-2022: A test negative design-based evaluation

Influenza vaccination is the most cost-effective strategy for influenza prevention. Influenza vaccines have been found to be effective against symptomatic and medically attended outpatient influenza illnesses. However, there is currently a lack of data regarding the effectiveness of inactivated influenza vaccines in Chongqing, China. We conducted a prospective observational test-negative design study. Outpatient and emergency cases presenting with influenza-like illnesses (ILI) and available influenza reverse transcription polymerase chain reaction (RT-PCR) were selected and classified as cases (positive influenza RT-PCR) or controls (negative influenza RT-PCR). A total of 7,307 cases of influenza and 7,905 control subjects were included in this study. The overall adjusted influenza vaccine effectiveness (IVE) was 44.4% (95% confidence interval (CI): 32.5-54.2%). In the age groups of less than 6 years old, 6-18 years old, and 19-59 years old, the adjusted IVE were 32.2% (95% CI: 10.0-48.9%), 48.2% (95% CI: 30.6-61.4%), and 72.0% (95% CI: 43.6-86.1%). The adjusted IVE for H1N1, H3N2 and B (Victoria) were 71.1% (95% CI: 55.4-81.3%), 36.1% (95% CI: 14.6-52.2%) and 33.7% (95% CI: 14.6-48.5%). Influenza vaccination was effective in Chongqing from 2018 to 2022. Evaluating IVE in this area is feasible and should be conducted annually in the future.

Revisiting the dimensions of universal vaccine with special focus on COVID-19: Efficacy versus methods of designing

Even though the use of SARS-CoV-2 vaccines during the COVID-19 pandemic showed unprecedented success in a short time, it also exposed a flaw in the current vaccine design strategy to offer broad protection against emerging variants of concern. However, developing broad-spectrum vaccines is still a challenge for immunologists. The development of universal vaccines against emerging pathogens and their variants appears to be a practical solution to mitigate the economic and physical effects of the pandemic on society. Very few reports are available to explain the basic concept of universal vaccine design and development. This review provides an overview of the innate and adaptive immune responses generated against vaccination and essential insight into immune mechanisms helpful in designing universal vaccines targeting influenza viruses and coronaviruses. In addition, the characteristics, safety, and factors affecting the efficacy of universal vaccines have been discussed. Furthermore, several advancements in methods worthy of designing universal vaccines are described, including chimeric immunogens, heterologous prime-boost vaccines, reverse vaccinology, structure-based antigen design, pan-reactive antibody vaccines, conserved neutralizing epitope-based vaccines, mosaic nanoparticle-based vaccines, etc. In addition to the several advantages, significant potential constraints, such as defocusing the immune response and subdominance, are also discussed.

Transforming vaccinology

The COVID-19 pandemic placed the field of vaccinology squarely at the center of global consciousness, emphasizing the vital role of vaccines as transformative public health tools. The impact of vaccines was recently acknowledged by the award of the 2023 Nobel Prize in Physiology or Medicine to Katalin Kariko and Drew Weissman for their seminal contributions to the development of mRNA vaccines. Here, we provide a historic perspective on the key innovations that led to the development of some 27 licensed vaccines over the past two centuries and recent advances that promise to transform vaccines in the future. Technological revolutions such as reverse vaccinology, synthetic biology, and structure-based design transformed decades of vaccine failures into successful vaccines against meningococcus B and respiratory syncytial virus (RSV). Likewise, the speed and flexibility of mRNA vaccines profoundly altered vaccine development, and the advancement of novel adjuvants promises to revolutionize our ability to tune immunity. Here, we highlight exciting new advances in the field of systems immunology that are transforming our mechanistic understanding of the human immune response to vaccines and how to predict and manipulate them. Additionally, we discuss major immunological challenges such as learning how to stimulate durable protective immune response in humans.

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.

Safety and immunogenicity of the intranasal H3N2 M2-deficient single-replication influenza vaccine alone or coadministered with an inactivated influenza vaccine (Fluzone High-Dose Quadrivalent) in adults aged 65-85 years in the USA: a multicentre, randomised, double-blind, double-dummy, phase 1b trial

BACKGROUND

Older adults (aged ≥65 years) show increased susceptibility to severe disease with influenza virus infection, accounting for 70-85% of annual influenza-related fatalities in the USA. Stimulating mucosal antibodies and T cells might enhance the low vaccine effectiveness seen in older adults for currently licensed inactivated influenza vaccines, which induce mainly serum antibodies. We aimed to evaluate the safety and immunogenicity of the intranasal H3N2 M2-deficient single-replication (M2SR) vaccine, alone or coadministered with a licensed inactivated influenza vaccine (Fluzone High-Dose Quadrivalent; hereafter referred to as Fluzone HD), in older adults.

METHODS

In this multicentre, randomised, double-blind, double-dummy, phase 1b trial, individuals aged 65-85 years who were considered healthy or with stable chronic conditions with no recent (<6 months) influenza vaccinations were recruited from five clinical trial sites in the USA and randomly assigned (3:3:3:1) using a permuted block design to receive the H3N2 M2SR vaccine and Fluzone HD, the H3N2 M2SR vaccine and placebo, Fluzone HD and placebo, or placebo alone. All participants received a single intranasal spray and a single intramuscular injection, whether active or placebo, to maintain masking. The primary outcome was to assess the safety of H3N2 M2SR, administered alone or with Fluzone HD, in the safety analysis set, which included all participants who were randomly assigned and received treatment. Serum and mucosal antibodies were assessed as a secondary endpoint, and cell-mediated immunity as an exploratory endpoint, in participants in the per-protocol population, which included individuals in the safety analysis set without major protocol deviations. This trial is registered with ClinicalTrials.gov, NCT05163847.

FINDINGS

Between June 14 and Sept 15, 2022, 305 participants were enrolled and randomly assigned to receive the H3N2 M2SR vaccine plus placebo (n=89), H3N2 M2SR vaccine plus Fluzone HD (n=94), Fluzone HD plus placebo (n=92), or placebo alone (n=30). All randomly assigned participants were included in the safety analysis set. The most frequently reported local symptoms up to day 8 in groups that received M2SR were rhinorrhoea (43% [38 of 89] in the H3N2 M2SR plus placebo group and 38% [36 of 94] in the H3N2 M2SR plus Fluzone HD group), nasal congestion (51% [45 of 89] and 35% [33 of 94]), and injection-site pain (8% [seven of 89] and 49% [46 of 94]), and the most frequently reported solicited systemic symptoms were sore throat (28% [25 of 89]) for M2SR and decreased activity (26% [24 of 94]) for the M2SR plus Fluzone HD group. In the Fluzone HD plus placebo group, the most frequently reported local symptom was injection-site pain (48% [44 of 92]) and systemic symptom was muscle aches (22% [20 of 92]). The frequency of participants with any treatment-emergent adverse event related to vaccination was low across all groups (2-5%). One serious adverse event was reported, in a participant in the Fluzone HD plus placebo group. M2SR with Fluzone HD induced seroconversion (≥four-fold increase in haemagglutination inhibition antibodies from baseline to day 29) in 44 (48%) of 91 participants, compared with 28 (31%) of 90 participants who seroconverted in the Fluzone HD plus placebo group (p=0·023). M2SR with Fluzone HD also induced mucosal and cellular immune responses.

INTERPRETATION

The H3N2 M2SR vaccine coadministered with Fluzone HD in older adults was well tolerated and provided enhanced immunogenicity compared with Fluzone HD administered alone, suggesting potential for improved efficacy of influenza vaccination in this age group. Additional studies are planned to assess efficacy.

FUNDING

US Department of Defense.

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.

The safety and immunogenicity of vaccines administered to pregnant women living with HIV: a systematic review and meta-analysis

Background

Human Immunodeficiency Virus (HIV)-exposed uninfected (HEU) infants have a higher burden of infectious diseases related morbidity and mortality compared with HIV-unexposed uninfected (HUU). Immunization of pregnant women living with HIV (PWLWH) could reduce the severity and burden of infectious diseases for HEU in early infancy.

Methods

We conducted a systematic review of safety and immunogenicity of vaccines administered to PWLWH and meta-analyses to test the overall effect of immunogenicity comparing pregnant women without HIV (PWWH) to PWLWH. We searched MEDLINE, Embase, Web of Science, Virtual Health Library and Cochrane databases in accordance with PRISMA guidelines for randomized controlled trials and observational studies. Review articles, case series, conference abstracts, and animal studies were excluded. Studies were included from inception to 6th September 2023, with no language restrictions. Random effects meta-analyses were performed for immunogenicity using Review manager (RevMan) analysis software version 5.4.1, Geometric Mean Titer (GMT) values were transformed to obtain the mean and standard deviation within RevMan, the effect size was computed and reported as mean difference with respective 95% confidence intervals. The review was registered with PROSPERO CRD42021289081.

Findings

We included 12 articles, comprising 3744 pregnant women, 1714 were PWLWH given either influenza, pneumococcal or an investigational Group B streptococcal (GBS) vaccine. Five studies described safety outcomes, and no increase in adverse events was reported in PWLWH compared to PWWH. The GMT increase from baseline to 28-35 weeks post vaccination in HA units ranged from 12.4 (95% CI: 9.84-14.9) to 238.8 (95% CI: 0.35-477.9). Meta-analyses of influenza vaccines showed the pooled geometric mean difference in Hemagglutination Inhibition (HAI) titers post vaccination was 56.01 (95% CI: 45.01-67.01), p < 0.001. The increase was less in PWLWH when compared with PWWH: -141.76 (95% CI: -194.96, -88.55), p < 0.001.

Interpretation

There are limited data on the safety and immunogenicity of vaccines given to PWLWH making policy consideration in this group difficult when new vaccines are introduced. With new vaccines on the horizon, PWLWH need to be included in studies to promote vaccine confidence for this special population.

Funding

This work was funded by Medical Research Council Joint Clinical Trials Round 9 [MR/T004983/1].

Innovative translational platforms for rapid developing clinical vaccines against COVID-19 and other infectious disease

A vaccine is a biological preparation that contains the antigen capable of stimulating the immune system to form the defense against pathogens. Vaccine development often confronts big challenges, including time/energy-consuming, low efficacy, lag to pathogen emergence and mutation, and even safety concern. However, these seem now mostly conquerable through constructing the advanced translational platforms that can make innovative vaccines, sometimes, potentiated with a distinct multifunctional VADS (vaccine adjuvant delivery system), as evidenced by the development of various vaccines against the covid-19 pandemic at warp speed. Particularly, several covid-19 vaccines, such as the viral-vectored vaccines, mRNA vaccines and DNA vaccines, regarded as the innovative ones that are rapidly made via the high technology-based translational platforms. These products have manifested powerful efficacy while showing no unacceptable safety profile in clinics, allowing them to be approved for massive vaccination at also warp speed. Now, the proprietary translational platforms integrated with the state-of-the-art biotechnologies, and even the artificial intelligence (AI), represent an efficient mode for rapid making innovative clinical vaccines against infections, thus increasingly attracting interests of vaccine research and development. Herein, the advanced translational platforms for making innovative vaccines, together with their design principles and immunostimulatory efficacies, are comprehensively elaborated.

Current Progress of Severe Fever with Thrombocytopenia Syndrome Virus (SFTSV) Vaccine Development

SFTSV is an emerging tick-borne virus causing hemorrhagic fever with a case fatality rate (CFR) that can reach up to 27%. With endemic infection in East Asia and the recent spread of the vector tick to more than 20 states in the United States, the SFTSV outbreak is a globally growing public health concern. However, there is currently no targeted antiviral therapy or licensed vaccine against SFTSV. Considering the age-dependent SFTS pathogenesis and disease outcome, a sophisticated vaccine development approach is required to safeguard the elderly population from lethal SFTSV infection. Given the recent emergence of SFTSV, the establishment of animal models to study immunogenicity and protection from SFTS symptoms has only occurred recently. The latest research efforts have applied diverse vaccine development approaches-including live-attenuated vaccine, DNA vaccine, whole inactivated virus vaccine, viral vector vaccine, protein subunit vaccine, and mRNA vaccine-in the quest to develop a safe and effective vaccine against SFTSV. This review aims to outline the current progress in SFTSV vaccine development and suggest future directions to enhance the safety and efficacy of these vaccines, ensuring their suitability for clinical application.

Self-assembling Gn head ferritin nanoparticle vaccine provides full protection from lethal challenge of Dabie Bandavirus in aged ferrets

Dabie Bandavirus (DBV), previously known as Severe Fever with Thrombocytopenia Syndrome (SFTS) Virus, induces a characteristic thrombocytopenia with a mortality rate ranging from 12% to as high as 30%. The sero-prevalence of DBV in healthy people is not significantly different among age groups, but clinically diagnosed SFTS patients are older than ~50 years, suggesting that age is the critical risk factor for SFTS morbidity and mortality. Accordingly, our immune-competent ferret model demonstrates an age (>4 years old)-dependent DBV infection and pathogenesis that fully recapitulates human clinical manifestation. To protect the aged population from DBV-induced SFTS, vaccine should carry robust immunogenicity with high safety profile. Previous studies have shown that glycoproteins Gn/Gc are the most effective antigens for inducing both neutralizing antibody (NAb)- and T cell-mediated immunity and, thereby, protection. Here, we report the development of a protein subunit vaccine with 24-mer self-assembling ferritin (FT) nanoparticle to present DBV Gn head region (GnH) for enhanced immunogenicity. Anion exchange chromatography and size exclusion chromatography readily purified the GnH-FT nanoparticles to homogeneity with structural integrity. Mice immunized with GnH-FT nanoparticles induced robust NAb response and T-cell immunity against DBV Gn. Furthermore, aged ferrets immunized with GnH-FT nanoparticles were fully protected from DBV challenge without SFTS symptoms such as body weight loss, thrombocytopenia, leukopenia, and fatality. This study demonstrates that DBV GnH-FT nanoparticles provide an efficient vaccine efficacy in mouse and aged ferret models and should be an outstanding vaccine candidate targeted for the aged population against fatal DBV infection.

Estimated health and economic impact of using high-dose influenza vaccine on respiratory and circulatory plus respiratory hospitalizations of older adults in Australia

Background

Standard dose influenza vaccine provides moderate protection from infection, but with lower effectiveness among the elderly. High dose and adjuvanted vaccines (HD-TIV and aTIV) were developed to address this. This study aims to estimate the incremental health and economic impact of using HD-TIV (high dose trivalent vaccine) instead of aTIV (adjuvanted trivalent vaccine) on respiratory and circulatory plus respiratory hospitalizations of older people (≥65 years) in Australia.

Methods

This is a modelling study comparing predicted hospitalization outcomes in people receiving HD-TIV or aTIV during an average influenza season in Australia. Hospitalization records of Australian adults ≥65 years of age from 01 April to 30 November during 15 influenza seasons (2002-2017 excluding 2009, which was a pandemic) were extracted from the Australian Institute of Health and Welfare [AIHW] and used to calculate hospitalisation rates during an average season. Relative vaccine effectiveness data for aTIV and HD-TIV were used to estimate morbidity burden related to influenza.

Results

Between 2002 and 2017, the average respiratory hospitalization rate among older people during influenza season (April-November) was 3,445/100,000 population-seasons, with an average cost of AU$ 7,175 per admission. The average circulatory plus respiratory hospitalization rate among older Australian people during that time was 10,393/100,000 population-seasons, with an average cost of AU$ 7829 per admission. For older Australians, HD-TIV may avert an additional 6,315-9,410 respiratory admissions each year, with an incremental healthcare cost saving of AU$ 15.9-38.2 million per year compared to aTIV. Similar results were also noted for circulatory plus respiratory hospitalizations.

Conclusions

From the modelled estimations, HD-TIV was associated with less economic burden and fewer respiratory, and circulatory plus respiratory hospitalizations than aTIV for older Australians.

[Vaccination in old age: an overview]

Vaccinations against infectious diseases are a highly effective preventive measure, especially in old age due to the higher susceptibility to infections. As the effectiveness of vaccinations decreases in old age due to immune senescence but also due to comorbidities, specific, more immunogenic vaccines have been developed for this target group. In Germany, the Standing Commission on Vaccination (STIKO) publishes annually updated vaccination recommendations also specifically for the 60+ years age group. Since 2018, standard vaccinations for this group have included herpes zoster vaccination with adjuvanted inactivated vaccine. Since 2021, the use of the quadrivalent influenza high-dose vaccine is recommended for this age group. Currently, the annual COVID-19 vaccination and the single pneumococcal vaccination with the new 20-valent conjugate vaccine have been added as standard vaccinations. The free STIKO app provides an always up to date overview of standard and indicated vaccinations for all age groups.

Importance of adjuvant selection in tuberculosis vaccine development: Exploring basic mechanisms and clinical implications

The global emergency of unexpected pathogens, exemplified by SARS-CoV-2, has emphasized the importance of vaccines in thwarting infection and curtailing the progression of severe disease. The scourge of tuberculosis (TB), emanating from the Mycobacterium tuberculosis (Mtb) complex, has inflicted a more profound toll in terms of mortality and morbidity than any other infectious agents prior to the SARS-CoV-2 pandemic. Despite the existence of Bacillus Calmette-Guérin (BCG), the only licensed vaccine developed a century ago, its efficacy against TB remains unsatisfactory, particularly in preventing pulmonary Mtb infections in adolescents and adults. However, collaborations between academic and industrial entities have led to a renewed impetus in the development of TB vaccines, with numerous candidates, particularly subunit vaccines with specialized adjuvants, exhibiting promising outcomes in recent clinical studies. Adjuvants are crucial in modulating optimal immunological responses, by endowing immune cells with sufficient antigen and immune signals. As exemplified by the COVID-19 vaccine landscape, the interplay between vaccine efficacy and adverse effects is of paramount importance, particularly for the elderly and individuals with underlying ailments such as diabetes and concurrent infections. In this regard, adjuvants hold the key to optimizing vaccine efficacy and safety. This review accentuates the pivotal roles of adjuvants and their underlying mechanisms in the development of TB vaccines. Furthermore, we expound on the prospects for the development of more efficacious adjuvants and their synergistic combinations for individuals in diverse states, such as aging, HIV co-infection, and diabetes, by examining the immunological alterations that arise with aging and comparing them with those observed in younger cohorts.

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.

Self-assembling Gn head ferritin nanoparticle vaccine provides full protection from lethal challenge of Dabie bandavirus in aged ferrets

IMPORTANCE

Dabie bandavirus (DBV) is an emerging tick-borne virus that causes severe fever with thrombocytopenia syndrome (SFTS) in infected patients. Human SFTS symptoms progress from fever, fatigue, and muscle pain to the depletion of white blood cells and platelets with fatality rates up to 30%. The recent spread of its vector tick to over 20 states in the United States increases the potential for outbreaks of the SFTS beyond the East Asia. Thus, the development of vaccine to control this rapidly emerging virus is a high priority. In this study, we applied self-assembling ferritin (FT) nanoparticle to enhance the immunogenicity of DBV Gn head domain (GnH) as a vaccine target. Mice immunized with the GnH-FT nanoparticle vaccine induced potent antibody responses and cellular immunity. Immunized aged ferrets were fully protected from the lethal challenge of DBV. Our study describes the GnH-FT nanoparticle vaccine candidate that provides protective immunity against the emerging DBV infection.

Methionine enkephalin(MENK) upregulated memory T cells in anti-influenza response

Novel prophylactic drugs and vaccination strategies for protection against influenza virus should induce specific effector T-cell immune responses in pulmonary airways and peripheral lymphoid organs. Designing approaches that promote T-cell-mediated responses and memory T-cell differentiation would strengthen host resistance to respiratory infectious diseases. The results of this study showed that pulmonary delivery of MENK via intranasal administration reduced viral titres, upregulated opioid receptor MOR and DOR, increased the proportions of T-cell subsets including CD8+ T cells, CD8+ TEM cells, NP/PA-effector CD8+ TEM cells in bronchoalveolar lavage fluid and lungs, and CD4+/CD8+ TCM cells in lymph nodes to protect mice against influenza viral challenge. Furthermore, we demonstrated that, on the 10th day of infection, the proportions of CD4+ TM and CD8+ TM cells were significantly increased, which meant that a stable TCM and TEM lineage was established in the early stage of influenza infection. Collectively, our data suggested that MENK administered intranasally, similar to the route of natural infection by influenza A virus, could exert antiviral activity through upregulating T-cell-mediated adaptive immune responses against influenza virus.

Novel Influenza Vaccines: From Research and Development (R&D) Challenges to Regulatory Responses

Influenza vaccines faced significant challenges in achieving sufficient protective efficacy and production efficiency in the past. In recent decades, novel influenza vaccines, characterized by efficient and scalable production, advanced platforms, and new adjuvant technologies, have overcome some of these weaknesses and have been widely licensed. Furthermore, researchers are actively pursuing the development of next-generation and universal influenza vaccines to provide comprehensive protection against potential pandemic subtypes or strains. However, new challenges have emerged as these novel vaccines undergo evaluation and authorization. In this review, we primarily outline the critical challenges and advancements in research and development (R&D) and highlight the improvements in regulatory responses for influenza vaccines.

Humoral Response to the Acetalated Dextran M2e Vaccine is Enhanced by Antigen Surface Conjugation

The influenza A virus causes substantial morbidity and mortality worldwide every year and poses a constant threat of an emergent pandemic. Seasonal influenza vaccination strategies fail to provide complete protection against infection due to antigenic drift and shift. A universal vaccine targeting a conserved influenza epitope could substantially improve current vaccination strategies. The ectodomain of the matrix 2 protein (M2e) of influenza is a highly conserved epitope between virus strains but is also poorly immunogenic. Administration of M2e and the immunostimulatory stimulator of interferon genes (STING) agonist 3'3'-cyclic guanosine-adenosine monophosphate (cGAMP) encapsulated in microparticles made of acetalated dextran (Ace-DEX) has previously been shown to be effective for increasing the immunogenicity of M2e, primarily through T-cell-mediated responses. Here, the immunogenicity of Ace-DEX MPs delivering M2e was further improved by conjugating the M2e peptide to the particle surface in an effort to affect B-cell responses more directly. Conjugated or encapsulated M2e co-administered with Ace-DEX MPs containing cGAMP were used to vaccinate mice, and it was shown that two or three vaccinations could fully protect against a lethal influenza challenge, while only the surface-conjugated antigen constructs could provide some protection against lethal challenge with only one vaccination. Additionally, the use of a reducible linker augmented the T-cell response to the antigen. These results show the utility of conjugating M2e to the surface of a particle carrier to increase its immunogenicity for use as the antigen in a universal influenza vaccine.

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.

Hemagglutinin virus-like particles incorporated with membrane-bound cytokine adjuvants provide protection against homologous and heterologous influenza virus challenge in aged mice

BACKGROUND

Current influenza vaccines deliver satisfactory results in young people but are less effective in the elderly. Development of vaccines for an ever-increasing aging population has been an arduous challenge due to immunosenescence that impairs the immune response in the aged, both quantitatively and qualitatively.

RESULTS

To potentially enhance vaccine efficacy in the elderly, we investigated the immunogenicity and cross-protection of influenza hemagglutinin virus-like particles (HA-VLP) incorporated with glycosylphosphatidylinositol (GPI)-anchored cytokine-adjuvants (GPI-GM-CSF and GPI-IL-12) via protein transfer in aged mice. Lung viral replication against homologous and heterologous influenza viruses was significantly reduced in aged mice after vaccination with cytokine incorporated VLPs (HA-VLP-Cyt) in comparison to HA-VLP alone. Enhanced IFN-γ+CD4+ and IFN-γ+CD8+ T cell responses were also observed in aged mice immunized with HA-VLP-Cyt when compared to HA-VLP alone.

CONCLUSIONS

Cytokine-adjuvanted influenza HA-VLP vaccine induced enhanced protective response against homologous influenza A virus infection in aged mice. Influenza HA-VLP vaccine with GPI-cytokines also induced enhanced T cell responses correlating with better protection against heterologous infection in the absence of neutralizing antibodies. The results suggest that a vaccination strategy using cytokine-adjuvanted influenza HA-VLPs could be used to enhance protection against influenza A virus in the elderly.

Challenges in the Vaccination of the Elderly and Strategies for Improvement

In recent years, the elderly has become a rapidly growing proportion of the world's population as life expectancy is extending. Immunosenescence and inflammaging contribute to the increased risk of chronic non-communicable and acute infectious diseases. Frailty is highly prevalent in the elderly and is associated with an impaired immune response, a higher propensity to infection, and a lower response to vaccines. Additionally, the presence of uncontrolled comorbid diseases in the elderly also contributes to sarcopenia and frailty. Vaccine-preventable diseases that threaten the elderly include influenza, pneumococcal infection, herpes zoster, and COVID-19, which contribute to significant disability-adjusted life years lost. Previous studies had shown that conventional vaccines only yielded suboptimal protection that wanes rapidly in a shorter time. This article reviews published papers on several vaccination strategies that were developed for the elderly to solve these problems: more immunogenic vaccine formulations using larger doses of antigen, stronger vaccine adjuvants, recombinant subunit or protein conjugated vaccines, newly developed mRNA vaccines, giving booster shots, and exploring alternative routes of administration. Included also are several publications on senolytic medications under investigation to boost the immune system and vaccine response in the elderly. With all those in regard, the currently recommended vaccines for the elderly are presented.

Enhanced passive safety surveillance of the MF59-adjuvanted quadrivalent influenza vaccine in the elderly during the 2021/22 influenza season

In accordance with European directives, each year the enhanced safety surveillance (ESS) of seasonal influenza vaccines should be conducted in order to detect any potential increase in reactogenicity when the vaccine composition is updated or a new formulation becomes available. The objective of this passive ESS (EPSS) was to assess the frequency of spontaneously reported adverse events (AEs) following vaccination with the 2021/22 formulation of the MF59-adjuvanted quadrivalent influenza vaccine (aQIV) among older adults in Italy through the collection of data within a short time period (start of seasonal influenza vaccination) in order to monitor the reactogenicity of aQIV early in the season. All AEs reported within seven days following vaccination were analyzed by type and seriousness. In all, 1,059 vaccination cards were distributed to individuals aged ≥65 years. Only one, non-serious, spontaneous individual case safety report was submitted, yielding an overall rate of 0.9 per 1,000 doses administered. This report consisted of a reactogenic AE of pyrexia. The EPSS confirmed that the reactogenicity profile of aQIV was consistent with the known safety profile of the previous trivalent formulation. These optimal safety data could bolster public confidence in influenza vaccination and help to improve vaccination coverage.

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).

Exploration of influenza incidence prediction model based on meteorological factors in Lanzhou, China, 2014-2017

Humans are susceptible to influenza. The influenza virus spreads quickly and behave seasonally. The seasonality and spread of influenza are often associated with meteorological factors and have spatio-temporal differences. Based on the influenza cases and daily average meteorological factors in Lanzhou from 2014 to 2017, this study firstly aimed to analyze the characteristics of influenza incidence in Lanzhou and the impact of meteorological factors on influenza activities. Then, SARIMA(X) models for the prediction were established. The influenza cases in Lanzhou from 2014 to 2017 was more male than female, and the younger the age, the higher the susceptibility; the epidemic characteristics showed that there is a peak in winter, a secondary peak in spring, and a trough in summer and autumn. The influenza cases in Lanzhou increased with increasing daily pressure, decreasing precipitation, average relative humidity, hours of sunshine, average daily temperature and average daily wind speed. Low temperature was a significant driving factor for the increase of transmission intensity of seasonal influenza. The SARIMAX (1,0,0)(1,0,1)[12] multivariable model with average temperature has better prediction performance than the university model. This model is helpful to establish an early warning system, and provide important evidence for the development of influenza control policies and public health interventions.

T Cell Transcriptional Signatures of Influenza A/H3N2 Antibody Response to High Dose Influenza and Adjuvanted Influenza Vaccine in Older Adults

Older adults experience declining influenza vaccine-induced immunity and are at higher risk of influenza and its complications. For this reason, high dose (e.g., Fluzone) and adjuvanted (e.g., Fluad) vaccines are preferentially recommended for people age 65 years and older. However, T cell transcriptional activity shaping the humoral immune responses to Fluzone and Fluad vaccines in older adults is still poorly understood. We designed a study of 234 older adults (≥65 years old) who were randomly allocated to receive Fluzone or Fluad vaccine and provided blood samples at baseline and at Day 28 after immunization. We measured the humoral immune responses (hemagglutination inhibition/HAI antibody titer) to influenza A/H3N2 and performed mRNA-Seq transcriptional profiling in purified CD4+ T cells, in order to identify T cell signatures that might explain differences in humoral immune response by vaccine type. Given the large differences in formulation (higher antigen dose vs adjuvant), our hypothesis was that each vaccine elicited a distinct transcriptomic response after vaccination. Thus, the main focus of our study was to identify the differential gene expression influencing the antibody titer in the two vaccine groups. Our analyses identified three differentially expressed, functionally linked genes/proteins in CD4+ T cells: the calcium/calmodulin dependent serine/threonine kinase IV (CaMKIV); its regulator the TMEM38B/transmembrane protein 38B, involved in maintenance of intracellular Ca2+ release; and the transcriptional coactivator CBP/CREB binding protein, as regulators of transcriptional activity/function in CD4+ T cells that impact differences in immune response by vaccine type. Significantly enriched T cell-specific pathways/biological processes were also identified that point to the importance of genes/proteins involved in Th1/Th2 cell differentiation, IL-17 signaling, calcium signaling, Notch signaling, MAPK signaling, and regulation of TRP cation Ca2+ channels in humoral immunity after influenza vaccination. In summary, we identified the genes/proteins and pathways essential for cell activation and function in CD4+ T cells that are associated with differences in influenza vaccine-induced humoral immunity by vaccine type. These findings provide an additional mechanistic perspective for achieving protective immunity in older adults.

Poly-γ-glutamic acid/Alum adjuvanted pH1N1 vaccine-immunized aged mice exhibit a significant increase in vaccine efficacy with a decrease in age-associated CD8+ T cell proportion in splenocytes

Background

Highly contagious respiratory diseases caused by viral infections are a constantly emerging threat, particularly the elderly with the higher risk of developing serious complications. Vaccines are the best strategy for protection against influenza-related diseases. However, the elderly has lower vaccine efficacy than young population and the age-driven decline of the influenza vaccine efficacy remains unresolved.

Objectives

This study investigates the effect of an adjuvant, poly-γ-glutamic acid and alum (PGA/Alum) on vaccine efficacy in aged mice (18-months) and its mechanism is investigated using ovalbumin as a model antigen and a commercial pandemic H1N1 (pH1N1) flu vaccine. Antigen trafficking, dendritic cell (DC) activation, and the DC-mediated T cell activation were analyzed via in vivo imaging and flow cytometry. Antigen-specific humoral and cellular immune responses were evaluated in sera and splenocytes from the vaccinated mice. Also, we analyzed gene expression profiles of splenocytes from the vaccinated mice via single-cell transcriptome sequencing and evaluated the protective efficacy against pH1N1 virus challenge.

Results

Aged mice had lower antigen trafficking and DC activation than younger mice (6-weeks), which was ameliorated by PGA/Alum with increased antigen uptake and DC activation leading to improved antigen-specific IFN-γ⁺CD8⁺ T lymphocyte frequencies higher in the vaccinated aged mice, to a similar extent as PGA/Alum adjuvanted vaccine-immunized young mice. The results of single-cell transcriptome sequencing display that PGA/Alum also reduced the proportion of age-associated CD8⁺ T cell subsets and gene levels of inhibitory regulators in CD8⁺ T cells, which may play a role in the recovery of CD8⁺ T cell activation. Finally, PGA/Alum adjuvanted pH1N1 vaccine-immunized aged mice were completely protected (100% survival) compared to aged mice immunized with vaccine only (0% survival) after pH1N1 virus challenge, akin to the efficacy of the vaccinated young mice (100% survival).

Conclusions

PGA/Alum adjuvanted pH1N1 vaccine-immunized aged mice showed a significant increase in vaccine efficacy compared to aged mice administered with vaccine only. The enhanced vaccine efficacy by PGA/Alum is associated with significant increases of activation of DCs and effector CD8⁺ T cells and a decrease in age-associated CD8⁺ T cell proportion of splenocytes. Collectively, PGA/Alum adjuvanted flu vaccine may be a promising vaccine candidate for the elderly.

Supplementary information

The online version contains supplementary material available at 10.1186/s12979-022-00282-z.

Distinct immunological and molecular signatures underpinning influenza vaccine responsiveness in the elderly

Seasonal influenza outbreaks, especially in high-risk groups such as the elderly, represent an important public health problem. Prevailing inadequate efficacy of seasonal vaccines is a crucial bottleneck. Understanding the immunological and molecular mechanisms underpinning differential influenza vaccine responsiveness is essential to improve vaccination strategies. Here we show comprehensive characterization of the immune response of randomly selected elderly participants (≥ 65 years), immunized with the adjuvanted influenza vaccine Fluad. In-depth analyses by serology, multi-parametric flow cytometry, multiplex and transcriptome analysis, coupled to bioinformatics and mathematical modelling, reveal distinguishing immunological and molecular features between responders and non-responders defined by vaccine-induced seroconversion. Non-responders are specifically characterized by multiple suppressive immune mechanisms. The generated comprehensive high dimensional dataset enables the identification of putative mechanisms and nodes responsible for vaccine non-responsiveness independently of confounding age-related effects, with the potential to facilitate development of tailored vaccination strategies for the elderly.

Enhancing Immunogenicity of Influenza Vaccine in the Elderly through Intradermal Vaccination: A Literature Analysis

BACKGROUND

Aging and immunosenescence lead to a gradual decline in immune responses in the elderly and the immunogenicity of influenza vaccines in this age group is sub-optimal. Several approaches have been explored to enhance the immunogenicity of influenza vaccines in the elderly, including incorporating vaccine adjuvant, increasing antigen dosage, and changing the route of vaccine administration.

METHOD

We systematically compared the immunogenicity and safety of influenza vaccines administered by intradermal (ID) route and either intramuscular (IM) or subcutaneous (SC) routes in older adults aged ≥ 65.

RESULTS

Of 17 studies included in this analysis, 3 studies compared the immunogenicity of ID vaccination to that of SC vaccination and 14 studies compared ID and IM vaccinations. ID vaccination was typically more immunogenic than both IM and SC routes at the same dosage. Importantly, a minimum of 3 µg of hemagglutinin antigen could be formulated in an ID influenza vaccine without a significant loss of immunogenicity. ID administration of standard-dose, unadjuvanted influenza vaccine was as immunogenic as IM injection of adjuvanted influenza vaccine. Waning of influenza-specific immunity was significant after 6 months, but there was no difference in waning immunity between vaccinations in ID, IM, or SC routes. While ID vaccination elicited local adverse reactions more frequently than other routes, these reactions were mild and lasted for no more than 3 days.

CONCLUSIONS

We conclude that ID vaccination is superior to IM or SC routes and may be a suitable approach to compensate for the reduced immunogenicity observed in elderly adults. We also conclude that the main benefit of ID influenza vaccine lies in its dose-sparing effect. Additional research is still needed to further develop a more immunogenic ID influenza vaccine.

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.

Evaluation of the 2018-2019 vaccine effectiveness against medically attended influenza-like illness using medical records and claims data

BACKGROUND

Healthcare administrative databases are a rich source of information that could be leveraged to estimate real-world influenza vaccine effectiveness (VE). We aimed to evaluate the VE of standard egg-based influenza vaccines and determine if administrative healthcare data provide accurate VE estimates compared to the US CDC data.

METHODS

This retrospective cohort study was conducted during the 2018-2019 influenza season. Individuals who had at least one relevant record per year between 2015 and 2019 in their electronic medical record were included. Individuals were considered protected 14 days after receiving an influenza vaccine. The outcome was the occurrence of medically attended influenza-like illness (MA-ILI) defined by clinical diagnostic codes. Adjusted odds ratios (aORs) were derived from multivariate logistic regression and adjusted VE (aVEs) were calculated using 100 × (1-aORs).

RESULTS

A total of 5,066,980 individuals were included in the analysis with 1,307,702 (25.8%) considered vaccinated. Overall, the median age was 54 (IQR, 32-66) and 58.1% were female. Vaccine protection against MA-ILI was moderate in children and low in adults. All estimates were lower than VEs reported by the CDC for the 2018-2019 influenza season. Our results were robust to potential loss to follow up, but misclassification bias and residual confounding led to underestimation of the 2018-2019 aVE. When stratified by the number of primary care visits, aVE estimates and vaccination coverage increased with the number of primary care visits, reaching estimates similar to those obtained by the US CDC and US national vaccination coverage among those with ≥ 6 primary care visits, resulting in significant positive vaccine protection in frequent healthcare users.

CONCLUSIONS

Moderate and low aVEs were observed during the 2018-2019 season using administrative healthcare data, which was likely due to detection and misclassification biases, correlated with healthcare seeking behaviour, leading to an underestimation of the 2018-2019 influenza VE.

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.

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.

The role of cell-mediated immunity against influenza and its implications for vaccine evaluation

Influenza vaccines remain the most effective tools to prevent flu and its complications. Trivalent or quadrivalent inactivated influenza vaccines primarily elicit antibodies towards haemagglutinin and neuraminidase. These vaccines fail to induce high protective efficacy, in particular in older adults and immunocompromised individuals and require annual updates to keep up with evolving influenza strains (antigenic drift). Vaccine efficacy declines when there is a mismatch between its content and circulating strains. Current correlates of protection are merely based on serological parameters determined by haemagglutination inhibition or single radial haemolysis assays. However, there is ample evidence showing that these serological correlates of protection can both over- or underestimate the protective efficacy of influenza vaccines. Next-generation universal influenza vaccines that induce cross-reactive cellular immune responses (CD4+ and/or CD8+ T-cell responses) against conserved epitopes may overcome some of the shortcomings of the current inactivated vaccines by eliciting broader protection that lasts for several influenza seasons and potentially enhances pandemic preparedness. Assessment of cellular immune responses in clinical trials that evaluate the immunogenicity of these new generation vaccines is thus of utmost importance. Moreover, studies are needed to examine whether these cross-reactive cellular immune responses can be considered as new or complementary correlates of protection in the evaluation of traditional and next-generation influenza vaccines. An overview of the assays that can be applied to measure cell-mediated immune responses to influenza with their strengths and weaknesses is provided here.

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.

A Cohort Study on Influenza Vaccine and All-Cause Mortality in Older Adults: Methodological Concerns and Public Health Implications

Introduction

In 2020, the restrictions adopted to control the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic led to an unprecedented reduction in influenza-related burden. As such, the reduced chance to characterize the circulating virus strains might have increased the risk of vaccine mismatch for the forthcoming winter seasons. The role of an effective influenza vaccination campaign might therefore assume even more value, especially for frail and multimorbid older individuals. Methodological concerns on confounding by indication are always debated in vaccine effectiveness studies and it might be instrumental to give a pragmatic message on an individual’s responsibility to receive the influenza vaccine. We therefore investigated the role of specific confounders to explain the association between influenza vaccine and mortality among older adults.

Methods

Using a primary care database, we formed a cohort of patients aged 65 years or older who were actively registered with their general practitioner (GP) at the beginning of each of nine influenza seasons through to the 2018/2019 season. The study index date was the related seasons’ starting date. Exposure to the influenza vaccine was operationally defined in the 2 months preceding the index date up to 2 weeks before the exit date. Cox regression models were estimated to calculate hazard ratios (HRs) and their 95% confidence intervals (CI) of death between vaccinated and unvaccinated patients in a time-dependent fashion. The potential confounders sequentially entered the model based on their increasing effect size observed in univariate analyses.

Results

Over the 10 years under study, the influenza vaccine showed a significant protective effect in terms of mortality, reaching 13% reduction (HR 0.87, 95% CI 0.80–0.95) in the 2018/2019 influenza season. When we estimated the multivariate model by sequentially adding the potential confounders, there was an inversion of HR (below the unit) that was significantly explained by the covariates coding for a prior history of lower respiratory tract infections and the presence of the pneumococcal vaccine.

Conclusion

In the current pandemic scenario, we cannot divert attention to proper use of face masks, social distancing, and hand hygiene, which are important measures to prevent influenza and other respiratory viral infections. Nonetheless, their effectiveness might be negligible without acceptable coverage for influenza vaccine, especially in older patients with a history of lower respiratory tract infections, which appears to be the main source of confounding by indication.

Multiplexed electrospray enables high throughput production of cGAMP microparticles to serve as an adjuvant for a broadly acting influenza vaccine

Subunit vaccines employing designer antigens such as Computationally Optimized Broadly Reactive Antigen (COBRA) hemagglutinin (HA) hold the potential to direct the immune response toward more effective and broadly-neutralizing targets on the Influenza virus. However, subunit vaccines generally require coadministration with an adjuvant to elicit a robust immune response. One such adjuvant is the stimulator of interferon genes (STING) agonist cyclic dinucleotide 3'3'-cyclic guanosine monophosphate-adenosine monophosphate (cGAMP). We have shown that encapsulation of cGAMP in acetalated dextran (Ace-DEX) microparticles through electrospray results in significantly greater biological activity. Electrospray is a continuous manufacturing process which achieves excellent encapsulation efficiency. However, the throughput of electrospray with a single spray head is limited. Here we report the development of a multiplexed electrospray apparatus with an order of magnitude greater throughput than a single-head apparatus. Physicochemical characterization and evaluation of adjuvant activity in vitro and in vivo indicated that microparticles produced with the higher throughput process are equally suited for use as a potent vaccine adjuvant to induce a balanced immune response to COBRA HA antigens.

A Phase 1/2 Study of a Respiratory Syncytial Virus Prefusion F Vaccine With and Without Adjuvant in Healthy Older Adults

BACKGROUND

Respiratory syncytial virus (RSV) is an important cause of disease in older adults. We evaluated the safety and immunogenicity of a stabilized RSV prefusion F subunit (RSVpreF) vaccine candidate with/without adjuvant in adults aged 65-85 years.

METHODS

Primary cohort participants were equally randomized to 1 of 7 RSVpreF formulations: 60 µg with either Al(OH)3 or CpG/Al(OH)3, 120 µg with either Al(OH)3 or CpG/Al(OH)3, 240 µg with either Al(OH)3 or CpG/Al(OH)3, 240 µg unadjuvanted, or placebo, administered concomitantly with high-dose seasonal inactivated influenza vaccine (SIIV). Participants in the month 0,2 cohort were randomized to RSVpreF 240 µg with CpG/Al(OH)3 or placebo, administered at months 0 and 2.

RESULTS

All RSVpreF vaccine candidates elicited robust and persistent serum neutralizing responses when administered alone or with SIIV. There was no notable difference in neutralizing response between the formulations, including those containing CpG. In the month 0,2 cohort, there was no booster effect of dose 2. SIIV responses were similar or slightly lower with concomitant administration of RSVpreF. Most systemic and local reactions were mild and more frequent after RSVpreF than placebo.

CONCLUSIONS

RSVpreF formulations were well tolerated and elicited robust neutralizing responses in older adults; however, CpG/Al(OH)3 did not further enhance responses. Clinical Trials Registration. NCT03572062.

Risk for Shoulder Conditions After Vaccination: A Population-Based Study Using Real-World Data

BACKGROUND

Although shoulder conditions have been reported as an adverse event after intramuscular vaccination in the deltoid muscle, epidemiologic data on shoulder conditions after vaccination are limited.

OBJECTIVE

To estimate the risk for shoulder conditions after vaccination and assess possible risk factors.

DESIGN

Retrospective cohort study.

SETTING

Kaiser Permanente Southern California, a large integrated health care organization.

PARTICIPANTS

Kaiser Permanente Southern California members aged 3 years or older who had an intramuscular vaccination administered in the deltoid muscle between 1 April 2016 and 31 December 2017.

MEASUREMENTS

A natural language processing (NLP) algorithm was used to identify potential shoulder conditions among vaccinated persons with shoulder disorder diagnosis codes. All NLP-identified cases were manually chart confirmed on the basis of our case definition. The characteristics of vaccinated persons with and without shoulder conditions were compared.

RESULTS

Among 3 758 764 administered vaccinations, 371 cases of shoulder condition were identified, with an estimated incidence of 0.99 (95% CI, 0.89 to 1.09) per 10 000 vaccinations. The incidence was 1.22 (CI, 1.10 to 1.35) for the adult (aged ≥18 years) and 0.05 (CI, 0.02 to 0.14) for the pediatric (aged 3 to 17 years) vaccinated populations. In the adult vaccinated population, advanced age, female sex, an increased number of outpatient visits in the 6 months before vaccination, lower Charlson Comorbidity Index, and pneumococcal conjugate vaccine were associated with a higher risk for shoulder conditions. Among influenza vaccines, quadrivalent vaccines were associated with an increased risk for shoulder conditions. Simultaneous administration of vaccines was associated with a higher risk for shoulder conditions among elderly persons.

LIMITATION

Generalizability to other health care settings, use of administrative data, and residual confounding.

CONCLUSION

These population-based data suggest a small absolute risk for shoulder conditions after vaccination. Given the high burden of shoulder conditions, clinicians should pay attention to any factors that may further increase risks.

PRIMARY FUNDING SOURCE

Centers for Disease Control and Prevention.

Precision Vaccine Adjuvants for Older Adults: A Scoping Review

Older adults, defined as those ≥60 years of age, are a growing population vulnerable to infections including severe acute respiratory syndrome coronavirus 2. Although immunization is a key to protecting this population, immunosenescence can impair responses to vaccines. Adjuvants can increase the immunogenicity of vaccine antigens but have not been systematically compared in older adults. We conducted a scoping review to assess the comparative effectiveness of adjuvants in aged populations. Adjuvants AS01, MF59, AS03, and CpG-oligodeoxynucleotide, included in licensed vaccines, are effective in older human adults. A growing menu of investigational adjuvants, such as Matrix-M and CpG plus alum, showed promising results in early phase clinical trials and preclinical studies. Most studies assessed only 1 or 2 adjuvants and no study has directly compared >3 adjuvants among older adults. Enhanced preclinical approaches enabling direct comparison of multiple adjuvants including human in vitro modeling and age-specific animal models may derisk and accelerate vaccine development for older adults.

Immunosenescence and Altered Vaccine Efficiency in Older Subjects: A Myth Difficult to Change

Organismal ageing is associated with many physiological changes, including differences in the immune system of most animals. These differences are often considered to be a key cause of age-associated diseases as well as decreased vaccine responses in humans. The most often cited vaccine failure is seasonal influenza, but, while it is usually the case that the efficiency of this vaccine is lower in older than younger adults, this is not always true, and the reasons for the differential responses are manifold. Undoubtedly, changes in the innate and adaptive immune response with ageing are associated with failure to respond to the influenza vaccine, but the cause is unclear. Moreover, recent advances in vaccine formulations and adjuvants, as well as in our understanding of immune changes with ageing, have contributed to the development of vaccines, such as those against herpes zoster and SARS-CoV-2, that can protect against serious disease in older adults just as well as in younger people. In the present article, we discuss the reasons why it is a myth that vaccines inevitably protect less well in older individuals, and that vaccines represent one of the most powerful means to protect the health and ensure the quality of life of older adults.

An old problem with new solutions: Strategies to improve vaccine efficacy in the elderly

Vaccination is the most effective measure to protect against infections. However, with increasing age, there is a progressive decline in the ability of the immune system to both protect against infection and develop protective immunity from vaccination. This age-related decline of the immune system is due to age-related changes in both the innate and adaptive immune systems. With an aging world population and increased risk of pandemics, there is a need to continue to develop strategies to increase vaccine responses in the elderly. Here, the major age-related changes that occur in both the innate and adaptive immune responses that impair the response to vaccination in the elderly will be highlighted. Existing and future strategies to improve vaccine efficacy in the elderly will then be discussed, including adjuvants, delivery methods, and formulation. These strategies provide mechanisms to improve the efficacy of existing vaccines and develop novel vaccines for the elderly.

Influenza vaccination of home health care staff and the impact on patient hospitalizations

BACKGROUND

Influenza is associated with significant morbidity and mortality for adults aged 65 years and older. Influenza vaccination of health care workers is recommended. There is limited evidence regarding influenza vaccinations among health care workers in the home health care (HHC) setting and their impact on HHC patient outcomes.

METHODS

A national survey of HHC agencies was conducted in 2018-2019 and linked with patient data from the Centers for Medicare and Medicaid Services. Adjusted logistic regression models were used to estimate the association between hospital transfers due to respiratory infection during a 60 day HHC episode and staff vaccination policies.

RESULTS

Only 26.2% of HHC agencies had staff vaccination requirements and 71.2% agencies had staff vaccination rates higher than 75%. Agency policies for staff influenza vaccination were associated with reduced hospital transfers due to respiratory infection among HHC patients.

DISCUSSION

Influenza vaccination rates among HHC staff were low during the 2017-2018 influenza season. Policymakers may consider vaccination mandates to improve health care worker vaccination rates and protect patient safety.

CONCLUSIONS

This study sheds light on the potential impact of COVID-19 vaccination among HHC workers on patient outcomes. COVID-19 vaccination mandates could prove to be a vital tool in the fight against COVID-19 variants and infection outbreaks.

Comparative efficacy and safety of vaccines to prevent seasonal influenza: A systematic review and network meta-analysis

Background

Influenza is one of the most common respiratory viral infections worldwide. Numerous vaccines are used to prevent influenza. Their selection should be informed by the best available evidence. We aimed to estimate the comparative efficacy and safety of seasonal influenza vaccines in children, adults and the elderly.

Methods

We conducted a systematic review and network meta-analysis (NMA). We searched the Cochrane Library Central Register of Controlled Trials, MEDLINE and EMBASE databases, and websites of regulatory agencies, through December 15th, 2020. We included placebo- or no vaccination-controlled, and head-to-head randomized clinical trials (RCTs). Pairs of reviewers independently screened the studies, abstracted the data, and appraised the risk of bias in accordance to the Cochrane Handbook for Systematic Reviews of Interventions. The primary outcome was laboratory-confirmed influenza. We also synthesized data for hospitalization, mortality, influenza-like illness (ILI), pneumonia or lower respiratory-tract disease, systemic and local adverse events (AEs). We estimated summary risk ratios (RR) using pairwise and NMA with random effects. This study is registered with PROSPERO, number CRD42018091895.

Findings

We identified 13,439 citations. A total of 231 RCTs were included after screening: 11 studies did not provide useful data for the analysis; 220 RCTs [100,677 children (< 18 years) and 329,127 adults (18-60 years) and elderly (≥ 61 years)] were included in the NMA. In adults and the elderly, all vaccines, except the trivalent inactivated intradermal vaccine (3-IIV ID), were more effective than placebo in reducing the risk of laboratory-confirmed influenza, with a RR between 0.33 (95% credible interval [CrI] 0.21-0.55) for trivalent inactivated high-dose (3-IIV HD) and 0.56 (95% CrI 0.41-0.74) for trivalent live-attenuated vaccine (3-LAIV). In adults and the elderly, compared with trivalent inactivated vaccine (3-IIV), no significant differences were found for any, except 3-LAIV, which was less efficacious [RR 1.41 (95% CrI 1.04-1.88)]. In children, compared with placebo, RR ranged between 0.13 (95% CrI 0.03-0.51) for trivalent inactivated vaccine adjuvanted with MF59/AS03 and 0.55 (95% CrI 0.36-0.83) for trivalent inactivated vaccine. Compared with 3-IIV, 3-LAIV and trivalent inactivated adjuvanted with MF59/AS03 were more efficacious [RR 0.52 (95% CrI 0.32-0.82) and RR 0.23 (95% CrI 0.06-0.87)] in reducing laboratory-confirmed influenza. With regard to safety, higher systemic AEs rates after vaccination with 3-IIV, 3-IIV HD, 3-IIV ID, 3-IIV MF59/AS03-adj, quadrivalent inactivated (4-IIV), quadrivalent adjuvanted (4-IIV MF59/AS03-adj), quadrivalent recombinant (4-RIV), 3-LAIV or quadrivalent live attenuated (4-LAIV) vaccines were noted in adults and the elderly [RR 1.5 (95% CrI 1.18-1.89) to 1.15 (95% CrI 1.06-1.23)] compared with placebo. In children, the systemic AEs rate after vaccination was not significantly higher than placebo.

Interpretation

All vaccines cumulatively achieved major reductions in the incidence of laboratory-confirmed influenza in children, adults, and the elderly. While the live-attenuated was more efficacious than the inactivated vaccine in children, many vaccine types can be used in adults and the elderly.

Funding

The directorate general of welfare, Lombardy region.

Analysis of R848 as an Adjuvant to Improve Inactivated Influenza Vaccine Immunogenicity in Elderly Nonhuman Primates

Elderly individuals are highly susceptible to developing severe outcomes as a result of influenza A virus (IAV) infection. This can be attributed to alterations that span the aged immune system, which also result in reduced responsiveness to the seasonal inactivated vaccine. Given the rapidly increasing number of individuals in this age group, it is imperative that we develop strategies that can better protect this population from IAV-associated disease. Based on our previous findings that the TLR7/8 agonist resiquimod (R848) could efficiently boost responses in the newborn, another population with decreased vaccine responsiveness, we evaluated this adjuvant in an elderly African green monkey (AGM) model. AGM aged 16-24 years old (equivalent to 64-96 in human years) were primed and boosted with inactivated A/PuertoRico/8/1934 (H1N1) (IPR8) alone or directly linked to R848 (IPR8-R848). We observed increases in the level of circulating virus-specific IgM antibody 10 days following primary vaccination in AGM that were vaccinated with IPR8-R848, but not IPR8 alone. In addition, there were significant increases in virus-specific IgG after boosting selectively in the IPR8-R848 vaccinated animals. These findings provide insights into the ability of R848 to modulate the aged immune system in the context of IAV vaccination.

Systematic review of the efficacy, effectiveness and safety of MF59® adjuvanted seasonal influenza vaccines for the prevention of laboratory-confirmed influenza in individuals ≥18 years of age

The most effective means of preventing seasonal influenza is through vaccination. In this systematic review, we investigated the efficacy, effectiveness and safety of MF59^® adjuvanted trivalent and quadrivalent influenza vaccines to prevent laboratory-confirmed influenza. A systematic literature search was conducted in electronic databases and grey literature sources up to 7 February 2020. Randomised controlled trials and non-randomised studies of interventions (NRSIs) were eligible for inclusion. The search returned 28,846 records, of which 48 studies on MF59^® adjuvanted vaccines met our inclusion criteria. No efficacy trials were identified. In terms of vaccine effectiveness (VE), MF59^® adjuvanted trivalent influenza vaccines were effective in preventing laboratory-confirmed influenza in older adults (aged ≥65 years) compared with no vaccination (VE = 45%, 95% confidence interval (CI) 23%-61%, 5 NRSIs across 3 influenza seasons). By subtype, significant effect was found for influenza A(H1N1) (VE = 61%, 95% CI 44%-73%) and B (VE = 29%, 95% CI 5%-46%), but not for A(H3N2). In terms of relative VE, there was no significant difference comparing MF59^® adjuvanted trivalent vaccines with either non-adjuvanted trivalent or quadrivalent vaccines. Compared with traditional trivalent influenza vaccines, MF59^® adjuvanted trivalent influenza vaccines were associated with a greater number of local adverse events (RR = 1.90, 95% CI 1.50-2.39) and systemic reactions (RR = 1.18, 95% CI 1.02-1.38). In conclusion, MF59^® adjuvanted trivalent influenza vaccines were found to be more effective than 'no vaccination'. Based on limited data, there was no significant difference comparing the effectiveness of MF59^® adjuvanted vaccines with their non-adjuvanted counterparts.

MAS-1, a novel water-in-oil adjuvant/delivery system, with reduced seasonal influenza vaccine hemagglutinin dose may enhance potency, durability and cross-reactivity of antibody responses in the elderly

BACKGROUND

Increased influenza vaccine efficacy is needed in the elderly at high-risk for morbidity and mortality due to influenza infection. Adjuvants may allow hemagglutinin (HA) dose-sparing with enhanced immunogenicity. MAS-1 is an investigational water-in-oil emulsion-based adjuvant/delivery system comprised of stable nanoglobular aqueous droplets.

METHODS

A phase 1, randomized, double-blind, safety and immunogenicity, adjuvant dose escalation trial was conducted in persons aged 65 years and older. MAS-1 adjuvant dose volumes at 0.3 mL or 0.5 mL containing 9 µg per HA derived from licensed seasonal trivalent influenza vaccine (IIV, Fluzone HD 60 µg per HA, Sanofi Pasteur) were compared to high dose (HD) IIV (Fluzone HD). Safety was measured by reactogenicity, adverse events, and safety laboratory measures. Immunogenicity was assessed by serum hemagglutination inhibition (HAI) antibody titers.

RESULTS

Forty-five subjects, aged 65-83 years, were randomly assigned to receive 9 µg per HA in 0.3 mL MAS-1 (15 subjects) or HD IIV (15 subjects) followed by groups randomly assigned to receive 9 µg per HA in 0.5 mL MAS-1 (10 subjects) or HD IIV (5 subjects). Injection site tenderness, induration, and pain, and headache, myalgia, malaise and fatigue were common, resolving before day 14 post-vaccination. Clinically significant late-onset injection site reactions occurred in four of ten subjects at the 0.5 mL adjuvant dose. Safety laboratory measures were within acceptable limits. MAS-1-adjuvanted IIV enhanced mean antibody titers, mean-fold increases in antibody titer, and seroconversion rates against vaccine strains for at least 168 days post-vaccination and enhanced cross-reactive antibodies against some non-study vaccine influenza viruses.

CONCLUSION

MAS-1 adjuvant provided HA dose-sparing without safety concerns at the 0.3 mL dose, but the 0.5 mL dose caused late injection site reactions. MAS-1-adjuvanted IIV induced higher HAI antibody responses with prolonged durability including against historical strains, thereby providing greater potential vaccine efficacy in the elderly throughout an influenza season. Clinical Trial Registry: ClinicalTrials.gov # NCT02500680.

Built-in adjuvants for use in vaccines

Vaccine refers to biological products that are produced using various pathogenic microorganisms for inoculation. The goal of vaccination is to induce a robust immune response against a specific antigen, thus preventing the organism from getting infected. In vaccines, adjuvants have been widely employed to enhance immunity against specific antigens. An ideal adjuvant should be stable, biodegradable, and low cost, not induce system rejection and promote an immune response. Various adjuvant components have been investigated across diverse applications. Typically, adjuvants are employed to meet the following objectives: (1) to improve the effectiveness of immunization with vaccines for specific populations, such as newborns and the elderly; (2) enhance the immunogenicity of highly purified or recombinant antigens; (3) allow immunization with a smaller dose of the vaccine, reducing drug dosage. In the present review, we primarily focus on chemically synthesized compounds that can be used as built-in adjuvants. We elaborate the classification of these compounds based on the induced immune activation mechanism and summarize their application in various vaccine types.

Adjuvants: Engineering Protective Immune Responses in Human and Veterinary Vaccines

Adjuvants are key components of many vaccines, used to enhance the level and breadth of the immune response to a target antigen, thereby enhancing protection from the associated disease. In recent years, advances in our understanding of the innate and adaptive immune systems have allowed for the development of a number of novel adjuvants with differing mechanisms of action. Herein, we review adjuvants currently approved for human and veterinary use, describing their use and proposed mechanisms of action. In addition, we will discuss additional promising adjuvants currently undergoing preclinical and/or clinical testing.

An exploratory study to assess patterns of influenza- and pneumonia-related mortality among the Italian elderly

Older adults are at disproportionately high risk of severe influenza-related outcomes and represent the main target of the annual influenza vaccination. The protective effect of seasonal influenza vaccination on the observed mortality indicators is controversial. In this ecological study, spatiotemporal patterns of pneumonia- and influenza-related mortality registered in the Italian elderly over seven (2011–2017) consecutive seasons were explored and the epidemiological association between the observed local pneumonia- and influenza-related mortality and influenza vaccination campaign features were modeled by using both fixed- and random-effects panel regression models. The descriptive spatiotemporal analysis showed a clear North–South gradient, where northern regions tended to report more pneumonia- and influenza-related deaths. After adjustment for potential confounders, it was found that each 1% increase in influenza vaccination coverage rate would be associated (P < .001) with a 1.6–1.9% decrease in pneumonia- and influenza-related mortality. Moreover, each 1% increase in the use of MF59®-adjuvanted trivalent influenza vaccine would be associated (P < .05) with a further 0.4% decrease in pneumonia- and influenza-related mortality. This study supports the increase in annual influenza vaccination in Italy and suggests that a higher level of use of the adjuvanted influenza vaccine in the elderly may be beneficial.