Seasonal Influenza Virus Vaccines Research Articles

Updated seasonal influenza and respiratory syncytial virus vaccine recommendations of the Advisory Committee on Immunization Practices - 2024

Updated seasonal influenza and respiratory syncytial virus vaccine recommendations of the Advisory Committee on Immunization Practices - 2024

Vaccination with antigenically complex hemagglutinin mixtures confers broad protection from influenza disease.

Current seasonal influenza virus vaccines induce responses primarily against immunodominant but highly plastic epitopes in the globular head of the hemagglutinin (HA) glycoprotein. Because of viral antigenic drift at these sites, vaccines need to be updated and readministered annually. To increase the breadth of influenza vaccine-mediated protection, we developed an antigenically complex mixture of recombinant HAs designed to redirect immune responses to more conserved domains of the protein. Vaccine-induced antibodies were disproportionally redistributed to the more conserved stalk of the HA without hindering, and in some cases improving, antibody responses against the head domain. These improved responses led to increased protection against homologous and heterologous viral challenges in both mice and ferrets compared with conventional vaccine approaches. Thus, antigenically complex protein mixtures can at least partially overcome HA head domain antigenic immunodominance and may represent a step toward a more universal influenza vaccine.

Chimeric hemagglutinin split vaccines elicit broadly cross-reactive antibodies and protection against group 2 influenza viruses in mice.

Seasonal influenza virus vaccines are effective when they are well matched to circulating strains. Because of antigenic drift/change in the immunodominant hemagglutinin (HA) head domain, annual vaccine reformulations are necessary to maintain a match with circulating strains. In addition, seasonal vaccines provide little to no protection against newly emerging pandemic strains. Sequential vaccination with chimeric HA (cHA) constructs has been proven to direct the immune response toward the immunosubdominant but more conserved HA stalk domain. In this study, we show that immunization with group 2 cHA split vaccines in combination with the CpG 1018 adjuvant elicits broadly cross-reactive antibodies against all group 2 HAs, as well as systemic and local antigen-specific T cell responses. Antibodies elicited after sequential vaccination are directed to conserved regions of the HA such as the stalk and the trimer interface and also to the N2 neuraminidase (NA). Immunized mice were fully protected from challenge with a broad panel of influenza A viruses.

A mosaic influenza virus-like particles vaccine provides broad humoral and cellular immune responses against influenza A viruses

The development of a universal influenza vaccine to elicit broad immune responses is essential in reducing disease burden and pandemic impact. In this study, the mosaic vaccine design strategy and genetic algorithms were utilized to optimize the seasonal influenza A virus (H1N1, H3N2) hemagglutinin (HA) and neuraminidase (NA) antigens, which also contain most potential T-cell epitopes. These mosaic immunogens were then expressed as virus-like particles (VLPs) using the baculovirus expression system. The immunogenicity and protection effectiveness of the mosaic VLPs were compared to the commercial quadrivalent inactivated influenza vaccine (QIV) in the mice model. Strong cross-reactive antibody responses were observed in mice following two doses of vaccination with the mosaic VLPs, with HI titers higher than 40 in 15 of 16 tested strains as opposed to limited cross HI antibody levels with QIV vaccination. After a single vaccination, mice also show a stronger level of cross-reactive antibody responses than the QIV. The QIV vaccinations only elicited NI antibodies to a small number of vaccine strains, and not even strong NI antibodies to its corresponding vaccine components. In contrast, the mosaic VLPs caused robust NI antibodies to all tested seasonal influenza virus vaccine strains. Here, we demonstrated the mosaic vaccines induces stronger cross-reactive antibodies and robust more T-cell responses compared to the QIV. The mosaic VLPs also provided protection against challenges with ancestral influenza A viruses of both H1 and H3 subtypes. These findings indicated that the mosaic VLPs were a promising strategy for developing a broad influenza vaccine in future.

Development of MDCK-based quadrivalent split seasonal influenza virus vaccine with high safety and immunoprotection: A preclinical study

Vaccination remains the best prevention strategy against influenza. The MDCK-based influenza vaccine prompted the development of innovative cell culture manufacturing processes. In the present study, we report the effects of multiple administrations of a candidate, seasonal, MDCK-based, quadrivalent split influenza virus vaccine MDCK-QIV in Sprague–Dawley (SD) rats. Moreover, the effects of the vaccine were evaluated in terms of fertility and early embryonic development, embryo–fetal development, and perinatal toxicity in the SD rats and immunogenicity in Wistar rats and BALB/c mice. Regarding the safety profile, MDCK-QIV demonstrated tolerance in local stimulation with repeated dose administration and presented no significant effect on the development, growth, behavior, fertility, and reproductive performance of the adult male rats, maternal rats, and their offspring. MDCK-QIV elicited strong hemagglutination inhibition neutralizing antibody response and protection against the influenza virus in the mouse model. Thus, data supported that MDCK-QIV could be further evaluated in human clinical trial, which is currently underway.

Generation of a high yield vaccine backbone for influenza B virus in embryonated chicken eggs

Influenza B virus (IBV) strains are one of the components of seasonal influenza vaccines in both trivalent and quadrivalent formulations. The vast majority of these vaccines are produced in embryonated chickens’ eggs. While optimized backbones for vaccine production in eggs exist and are in use for influenza A viruses, no such backbones exist for IBVs, resulting in unpredictable production yields. To generate an optimal vaccine seed virus backbone, we have compiled a panel of 71 IBV strains from 1940 to present day, representing the known temporal and genetic variability of IBV circulating in humans. This panel contains strains from the B/Victoria/2/87-like lineage, B/Yamagata/16/88-like lineage and the ancestral lineage that preceded their split to provide a diverse set that would help to identify a suitable backbone which can be used in combination with hemagglutinin (HA) and neuraminidase (NA) glycoproteins from any IBV strain to be incorporated into the seasonal vaccine. We have characterized and ranked the growth profiles of the 71 IBV strains and the best performing strains were used for co-infection of eggs, followed by serial passaging to select for high-growth reassortant viruses. After serial passaging, we selected 10 clonal isolates based on their growth profiles assessed by hemagglutination and plaque-forming units. We then generated reverse genetics systems for the three clones that performed best in growth curves. The selected backbones were then used to generate different reassortant viruses with HA/NA combinations from high and low titer yielding wild type IBV. When the growth profiles of the recombinant reassortant viruses were tested, the low titer yielding HA/NA viruses with the selected backbones yielded higher titers similar to those from high titer yielding HA/NA combinations. The use of these IBV backbones with improved replication in eggs might increase yields for the influenza B virus components of seasonal influenza virus vaccines.

Report on influenza viruses received and tested by the Melbourne WHO Collaborating Centre for Reference and Research on Influenza during 2022.

As part of its role in the World Health Organization's (WHO) Global Influenza Surveillance and Response System (GISRS), the WHO Collaborating Centre for Reference and Research on Influenza in Melbourne received a record total of 12,073 human influenza positive samples during 2022. Viruses were analysed for their antigenic, genetic and antiviral susceptibility properties. Selected viruses were propagated in qualified cells or embryonated hen's eggs for potential use in seasonal influenza virus vaccines. In 2022, influenza A(H3N2) viruses predominated over influenza A(H1N1)pdm09 and B viruses, accounting for 77% of all viruses analysed. The majority of A(H1N1)pdm09, A(H3N2) and influenza B viruses analysed at the Centre were found to be antigenically and genetically similar to the respective WHO recommended vaccine strains for the southern hemisphere in 2022. Of 3,372 samples tested for susceptibility to the neuraminidase inhibitors oseltamivir and zanamivir, two A(H1N1)pdm09 viruses showed highly reduced inhibition against oseltamivir.

Strategies targeting hemagglutinin cocktail as a potential universal influenza vaccine.

Vaccination is the most effective means of protecting people from influenza virus infection. The effectiveness of existing vaccines is very limited due to antigenic drift of the influenza virus. Therefore, there is a requirement to develop a universal vaccine that provides broad and long-lasting protection against influenza. CD8+ T-cell response played a vital role in controlling influenza virus infection, reducing viral load, and less clinical syndrome. In this study, we optimized the HA sequences of human seasonal influenza viruses (H1N1, H3N2, Victoria, and Yamagata) by designing multivalent vaccine antigen sets using a mosaic vaccine design strategy and genetic algorithms, and designed an HA mosaic cocktail containing the most potential CTL epitopes of seasonal influenza viruses. We then tested the recombinant mosaic antigen, which has a significant number of potential T-cell epitopes. Results from genetic evolutionary analyses and 3D structural simulations demonstrated its potential to be an effective immunogen. In addition, we have modified an existing neutralizing antibody-based seasonal influenza virus vaccine to include a component that activates cross-protective T cells, which would provide an attractive strategy for improving human protection against seasonal influenza virus drift and mutation and provide an idea for the development of a rationally designed influenza vaccine targeting T lymphocyte immunity.

Could seasonal Influenza virus vaccine reduce the risk and severity Of SARS-CoV-2 infection? - The first Egyptian experience

Could seasonal Influenza virus vaccine reduce the risk and severity Of SARS-CoV-2 infection? - The first Egyptian experience

A CpG 1018 adjuvanted neuraminidase vaccine provides robust protection from influenza virus challenge in mice

Influenza virus infections pose a significant threat to global health. Vaccination is the main countermeasure against influenza virus spread, however, the effectiveness of vaccines is variable. Current seasonal influenza virus vaccines mostly rely on the immunodominant hemagglutinin (HA) glycoprotein on the viral surface, which usually leads to a narrow and strain-specific immune response. The HA undergoes constant antigenic drift, which can lead to a dramatic loss in vaccine effectiveness, requiring the annual reformulation and readministration of influenza virus vaccines. Recently, it has been demonstrated that the subdominant glycoprotein, neuraminidase (NA), is an attractive target for vaccine development. Here, we tested a newly developed recombinant influenza virus N1 neuraminidase vaccine candidate, named N1-MPP, adjuvanted with CpG 1018, a TLR9 agonist. Additionally, N2-MPP and B-NA-MPP vaccine constructs have been generated to cover the range of influenza viruses that are seasonally circulating in humans. These constructs have been characterized in vitro and in vivo regarding their functionality and protective potential. Furthermore, a trivalent NA-MPP mix was tested. No antigenic competition between the individual NA constructs was detected. By adjuvating the recombinant protein constructs with CpG 1018 it was possible to induce a strong and robust immune response against the NA, which provided full protection against morbidity and mortality after high lethal challenges in vivo. This study provides important insights for the development of a broadly protective NA-based influenza virus vaccine candidate.

A Virion-Based Combination Vaccine Protects against Influenza and SARS-CoV-2 Disease in Mice.

ABSTRACTVaccines targeting SARS-CoV-2 have been shown to be highly effective; however, the breadth against emerging variants and the longevity of protection remains unclear. Postimmunization boosting has been shown to be beneficial for disease protection, and as new variants continue to emerge, periodic (and perhaps annual) vaccination will likely be recommended. New seasonal influenza virus vaccines currently need to be developed every year due to continual antigenic drift, an undertaking made possible by a robust global vaccine production and distribution infrastructure. To create a seasonal combination vaccine targeting both influenza viruses and SARS-CoV-2 that is also amenable to frequent reformulation, we have developed an influenza A virus (IAV) genetic platform that allows the incorporation of an immunogenic domain of the SARS-CoV-2 spike (S) protein onto IAV particles. Vaccination with this combination vaccine elicited neutralizing antibodies and provided protection from lethal challenge with both pathogens in mice. This approach may allow the leveraging of established influenza vaccine infrastructure to generate a cost-effective and scalable seasonal vaccine solution for both influenza and coronaviruses.IMPORTANCE The rapid emergence of SARS-CoV-2 variants since the onset of the pandemic has highlighted the need for both periodic vaccination “boosts” and a platform that can be rapidly reformulated to manufacture new vaccines. In this work, we report an approach that can utilize current influenza vaccine manufacturing infrastructure to generate combination vaccines capable of protecting from both influenza virus- and SARS-CoV-2-induced disease. The production of a combined influenza/SARS-CoV-2 vaccine may represent a practical solution to boost immunity to these important respiratory viruses without the increased cost and administration burden of multiple independent vaccines.

Healthcare Workers Should Receive Seasonal Influenza Vaccine during COVID-19 Pandemic?

It is known that seasonal influenza virus vaccination is important to be taken every year among healthcare workers (HCWs) to avoid transmission of influenza virus and its complications inside the workplace. The reason behind the importance of vaccination is that HCWs are at high risk to be infected with influenza virus. Among the studies addressing the rates of influenza vaccine status among HCWs, a study was conducted in three Middle East countries where the vaccination rates were 24.7%, 67.2%, and 46.4% in United Arab Emirates, Kuwait, and Oman, respectively. Now, after the pandemic of COVID-19 there are beliefs that vaccination with influenza virus could decrease the deaths from COVID-19. A recent retrospective cohort study to detect the effect of seasonal influenza vaccine on the deaths among COVID-19 patients showed that the individuals who didn’t take the influenza vaccine in the last year before being infected with COVID-19 had a higher risk of being hospitalized when compared with patients who took the vaccine. In conclusion, seasonal influenza vaccine could have an important role in the prevention of COVID-19. Seasonal influenza vaccine coverage should be improved among HCWs. New tailored health education programs to improve the attitudes and beliefs of HCWs towards seasonal influenza vaccine during the era of COVID-19 are strongly and urgently needed.

SARS-CoV-2 and Influenza A Virus Coinfections in Ferrets.

ABSTRACTSevere acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and seasonal influenza viruses are cocirculating in the human population. However, only a few cases of viral coinfection with these two viruses have been documented in humans with some people having severe disease and others mild disease. To examine this phenomenon, ferrets were coinfected with SARS-CoV-2 and human seasonal influenza A viruses (IAVs; H1N1 or H3N2) and were compared to animals that received each virus alone. Ferrets were either immunologically naive to both viruses or vaccinated with the 2019 to 2020 split-inactivated influenza virus vaccine. Coinfected naive ferrets lost significantly more body weight than ferrets infected with each virus alone and had more severe inflammation in both the nose and lungs compared to that of ferrets that were single infected with each virus. Coinfected, naive animals had predominantly higher IAV titers than SARS-CoV-2 titers, and IAVs were efficiently transmitted by direct contact to the cohoused ferrets. Comparatively, SARS-CoV-2 failed to transmit to the ferrets that cohoused with coinfected ferrets by direct contact. Moreover, vaccination significantly reduced IAV titers and shortened the viral shedding but did not completely block direct contact transmission of the influenza virus. Notably, vaccination significantly ameliorated influenza-associated disease by protecting vaccinated animals from severe morbidity after IAV single infection or IAV and SARS-CoV-2 coinfection, suggesting that seasonal influenza virus vaccination is pivotal to prevent severe disease induced by IAV and SARS-CoV-2 coinfection during the COVID-19 pandemic.IMPORTANCE Influenza A viruses cause severe morbidity and mortality during each influenza virus season. The emergence of SARS-CoV-2 infection in the human population offers the opportunity to potential coinfections of both viruses. The development of useful animal models to assess the pathogenesis, transmission, and viral evolution of these viruses as they coinfect a host is of critical importance for the development of vaccines and therapeutics. The ability to prevent the most severe effects of viral coinfections can be studied using effect coinfection ferret models described in this report.

A Novel Recombinant Influenza Virus Neuraminidase Vaccine Candidate Stabilized by a Measles Virus Phosphoprotein Tetramerization Domain Provides Robust Protection from Virus Challenge in the Mouse Model.

ABSTRACTCurrent seasonal influenza virus vaccines do not induce robust immune responses to neuraminidase. Several factors, including immunodominance of hemagglutinin over neuraminidase, instability of neuraminidase in vaccine formulations, and variable, nonstandardized amounts of neuraminidase in the vaccines, may contribute to this effect. However, vaccines that induce strong antineuraminidase immune responses would be beneficial, as they are highly protective. Furthermore, antigenic drift is slower for neuraminidase than for hemagglutinin, potentially providing broader coverage. Here, we designed stabilized recombinant versions of neuraminidase by replacing the N-terminal cytoplasmic domain, transmembrane, and extracellular stalk with tetramerization domains from the measles or Sendai virus phosphoprotein or from an Arabidopsis thaliana transcription factor. The measles virus tetramerization domain-based construct, termed N1-MPP, was chosen for further evaluation, as it retained antigenicity, neuraminidase activity, and structural integrity and provided robust protection in vivo against lethal virus challenge in the mouse model. We tested N1-MPP as a standalone vaccine, admixed with seasonal influenza virus vaccines, or given with seasonal influenza virus vaccines but in the other leg of the mouse. Admixture with different formulations of seasonal vaccines led to a weak neuraminidase response, suggesting a dominant effect of hemagglutinin over neuraminidase when administered in the same formulation. However, administration of neuraminidase alone or with seasonal vaccine administered in the alternate leg of the mouse induced robust antibody responses. Thus, this recombinant neuraminidase construct is a promising vaccine antigen that may enhance and broaden protection against seasonal influenza viruses.

Human B cell lineages associated with germinal centers following influenza vaccination are measurably evolving.

The poor efficacy of seasonal influenza virus vaccines is often attributed to pre-existing immunity interfering with the persistence and maturation of vaccine-induced B cell responses. We previously showed that a subset of vaccine-induced B cell lineages are recruited into germinal centers (GCs) following vaccination, suggesting that affinity maturation of these lineages against vaccine antigens can occur. However, it remains to be determined whether seasonal influenza vaccination stimulates additional evolution of vaccine-specific lineages, and previous work has found no significant increase in somatic hypermutation among influenza-binding lineages sampled from the blood following seasonal vaccination in humans. Here, we investigate this issue using a phylogenetic test of measurable immunoglobulin sequence evolution. We first validate this test through simulations and survey measurable evolution across multiple conditions. We find significant heterogeneity in measurable B cell evolution across conditions, with enrichment in primary response conditions such as HIV infection and early childhood development. We then show that measurable evolution following influenza vaccination is highly compartmentalized: while lineages in the blood are rarely measurably evolving following influenza vaccination, lineages containing GC B cells are frequently measurably evolving. Many of these lineages appear to derive from memory B cells. We conclude from these findings that seasonal influenza virus vaccination can stimulate additional evolution of responding B cell lineages, and imply that the poor efficacy of seasonal influenza vaccination is not due to a complete inhibition of vaccine-specific B cell evolution.

Influence of the H1N1 influenza pandemic on the humoral immune response to seasonal flu vaccines.

In this study, we hypothesized that the humoral response to trivalent seasonal influenza virus vaccines was influenced by rapid antigenic switching of H1 HA. We tested archived sera and peripheral blood mononuclear cells (PBMC) collected at prior to vaccination at day 0, as well as days 30 and 90 after vaccination during the 2009/2010 and 2010/2011 influenza virus seasons. During the 2009/2010 season, vaccination successfully induced antibodies with hemagglutinin inhibition (HAI) activity against both H1N1 and H3N2 vaccine components. For the 2010/2011 season, the A/California/04/2009 (CA/09) H1N1 elicited seroconversion (HAI titer = 1:40) and novel memory B cell (Bmem) responses from most individuals. However, the H3N2 influenza virus component of the vaccine, A/Perth/16/2009 (Perth/09), back-boosted and elicited antibodies with HAI activity and Bmem response to historical H3N2 influenza virus strains. Following stratification of the pre-existing antibody with HAI against the CA/09 H1N1, there was a negative correlation with HAI seroconversion to other vaccine strains. Overall, strong immune responses against CA/09 H1N1 influenza virus negatively influenced the induction of novel humoral responses.

Mosaic Hemagglutinin-Based Whole Inactivated Virus Vaccines Induce Broad Protection Against Influenza B Virus Challenge in Mice.

Influenza viruses undergo antigenic changes in the immuno-dominant hemagglutinin (HA) head domain, necessitating annual re-formulation of and re-vaccination with seasonal influenza virus vaccines for continuing protection. We previously synthesized mosaic HA (mHA) proteins of influenza B viruses which redirect the immune response towards the immuno-subdominant conserved epitopes of the HA via sequential immunization. As ~90% of current influenza virus vaccines are manufactured using the inactivated virus platform, we generated and sequentially vaccinated mice with inactivated influenza B viruses displaying either the homologous (same B HA backbones) or the heterologous (different B HA backbones) mosaic HAs. Both approaches induced long-lasting and cross-protective antibody responses showing strong antibody-dependent cellular cytotoxicity (ADCC) activity. We believe the B virus mHA vaccine candidates represent a major step towards a universal influenza B virus vaccine.

Report on influenza viruses received and tested by the Melbourne WHO Collaborating Centre for Reference and Research on Influenza in 2019.

As part of its role in the World Health Organization's (WHO) Global Influenza Surveillance and Response System (GISRS), the WHO Collaborating Centre for Reference and Research on Influenza in Melbourne received a record total of 9,266 human influenza positive samples during 2019. Viruses were analysed for their antigenic, genetic and antiviral susceptibility properties. Selected viruses were propagated in qualified cells or embryonated hen's eggs for potential use in seasonal influenza virus vaccines. In 2019, influenza A(H3N2) viruses predominated over influenza A(H1N1)pdm09 and B viruses, accounting for a total of 51% of all viruses analysed. The majority of A(H1N1)pdm09, A(H3N2) and influenza B viruses analysed at the Centre were found to be antigenically similar to the respective WHO recommended vaccine strains for the Southern Hemisphere in 2019. However, phylogenetic analysis indicated that a significant proportion of circulating A(H3N2) viruses had undergone genetic drift relative to the WHO recommended vaccine strain for 2019. Of 5,301 samples tested for susceptibility to the neuraminidase inhibitors oseltamivir and zanamivir, four A(H1N1)pdm09 viruses showed highly reduced inhibition with oseltamivir, one A(H1N1)pdm09 virus showed highly reduced inhibition with zanamivir and three B/Victoria viruses showed highly reduced inhibition with zanamivir.

Towards integrated production of an influenza A vaccine candidate with MDCK suspension cells.

Seasonal influenza epidemics occur both in northern and southern hemispheres every year. Despite the differences in influenza virus surface antigens and virulence of seasonal subtypes, manufacturers are well-adapted to respond to this periodical vaccine demand. Due to decades of influenza virus research, the development of new influenza vaccines is relatively straight forward. In similarity with the ongoing coronavirus disease 2019 pandemic, vaccine manufacturing is a major bottleneck for a rapid supply of the billions of doses required worldwide. In particular, egg-based vaccine production would be difficult to schedule and shortages of other egg-based vaccines with high demands also have to be anticipated. Cell culture-based production systems enable the manufacturing of large amounts of vaccines within a short time frame and expand significantly our options to respond to pandemics and emerging viral diseases. In this study, we present an integrated process for the production of inactivated influenza A virus vaccines based on a Madin-Darby Canine Kidney (MDCK) suspension cell line cultivated in a chemically defined medium. Very high titers of 3.6 log10 (HAU/100 µl) were achieved using fast-growing MDCK cells at concentrations up to 9.5 × 106 cells/ml infected with influenza A/PR/8/34 H1N1 virus in 1 L stirred tank bioreactors. A combination of membrane-based steric-exclusion chromatography followed by pseudo-affinity chromatography with a sulfated cellulose membrane adsorber enabled full recovery for the virus capture step and up to 80% recovery for the virus polishing step. Purified virus particles showed a homogenous size distribution with a mean diameter of 80 nm. Based on a monovalent dose of 15 µg hemagglutinin (single-radial immunodiffusion assay), the level of total protein and host cell DNA was 58 µg and 10 ng, respectively. Furthermore, all process steps can be fully scaled up to industrial quantities for commercial manufacturing of either seasonal or pandemic influenza virus vaccines. Fast production of up to 300 vaccine doses per liter within 4-5 days makes this process competitive not only to other cell-based processes but to egg-based processes as well.

Animal Models Utilized for the Development of Influenza Virus Vaccines.

Animal models have been an important tool for the development of influenza virus vaccines since the 1940s. Over the past 80 years, influenza virus vaccines have evolved into more complex formulations, including trivalent and quadrivalent inactivated vaccines, live-attenuated vaccines, and subunit vaccines. However, annual effectiveness data shows that current vaccines have varying levels of protection that range between 40–60% and must be reformulated every few years to combat antigenic drift. To address these issues, novel influenza virus vaccines are currently in development. These vaccines rely heavily on animal models to determine efficacy and immunogenicity. In this review, we describe seasonal and novel influenza virus vaccines and highlight important animal models used to develop them.