Cross-subtype immunity against avian influenza in persons recently vaccinated for influenza

Risk assessment of a highly pathogenic H5N1 influenza virus from mink

Outbreaks of highly pathogenic H5N1 clade 2.3.4.4b viruses in farmed mink and seals combined with isolated human infections suggest these viruses pose a pandemic threat. To assess this threat, using the ferret model, we show an H5N1 isolate derived from mink transmits by direct contact to 75% of exposed ferrets and, in airborne transmission studies, the virus transmits to 37.5% of contacts. Sequence analyses show no mutations were associated with transmission. The H5N1 virus also has a low infectious dose and remains virulent at low doses. This isolate carries the adaptive mutation, PB2 T271A, and reversing this mutation reduces mortality and airborne transmission. This is the first report of a H5N1 clade 2.3.4.4b virus exhibiting direct contact and airborne transmissibility in ferrets. These data indicate heightened pandemic potential of the panzootic H5N1 viruses and emphasize the need for continued efforts to control outbreaks and monitor viral evolution.

A computational approach to design a multiepitope vaccine against H5N1 virus

Since 1997, highly pathogenic avian influenza viruses, such as H5N1, have been recognized as a possible pandemic hazard to men and the poultry business. The rapid rate of mutation of H5N1 viruses makes the whole process of designing vaccines extremely challenging. Here, we used an in silico approach to design a multi-epitope vaccine against H5N1 influenza A virus using hemagglutinin (HA) and neuraminidase (NA) antigens. B-cell epitopes, Cytotoxic T lymphocyte (CTL) and Helper T lymphocyte (HTL) were predicted via IEDB, NetMHC-4 and NetMHCII-2.3 respectively. Two adjuvants consisting of Human β-defensin-3 (HβD-3) along with pan HLA DR-binding epitope (PADRE) have been chosen to induce more immune response. Linkers including KK, AAY, HEYGAEALERAG, GPGPGPG and double EAAAK were utilized to link epitopes and adjuvants. This construct encodes a protein having 350 amino acids and 38.46 kDa molecular weight. Antigenicity of ~ 1, the allergenicity of non-allergen, toxicity of negative and solubility of appropriate were confirmed through Vaxigen, AllerTOP, ToxDL and DeepSoluE, respectively. The 3D structure of H5N1 was refined and validated with a Z-Score of - 0.87 and an overall Ramachandran of 99.7%. Docking analysis showed H5N1 could interact with TLR7 (docking score of - 374.08 and by 4 hydrogen bonds) and TLR8 (docking score of - 414.39 and by 3 hydrogen bonds). Molecular dynamics simulations results showed RMSD and RMSF of 0.25 nm and 0.2 for H5N1-TLR7 as well as RMSD and RMSF of 0.45 nm and 0.4 for H5N1-TLR8 complexes, respectively. Molecular Mechanics Poisson-Boltzmann Surface Area (MM/PBSA) confirmed stability and continuity of interaction between H5N1-TLR7 with the total binding energy of - 29.97 kJ/mol and H5N1-TLR8 with the total binding energy of - 23.9 kJ/mol. Investigating immune response simulation predicted evidence of the ability to stimulate T and B cells of the immunity system that shows the merits of this H5N1 vaccine proposed candidate for clinical trials.

Insight into the first multi-epitope-based peptide subunit vaccine against avian influenza A virus (H5N6): An immunoinformatics approach

The rampant spread of highly pathogenic avian influenza A (H5N6) virus has drawn additional concerns along with ongoing Covid-19 pandemic. Due to its migration-related diffusion, the situation is deteriorating. Without an existing effective therapy and vaccines, it will be baffling to take control measures. In this regard, we propose a revers vaccinology approach for prediction and design of a multi-epitope peptide based vaccine. The induction of humoral and cell-mediated immunity seems to be the paramount concern for a peptide vaccine candidate; thus, antigenic B and T cell epitopes were screened from the surface, membrane and envelope proteins of the avian influenza A (H5N6) virus, and passed through several immunological filters to determine the best possible one. Following that, the selected antigenic with immunogenic epitopes and adjuvant were linked to finalize the multi-epitope-based peptide vaccine by appropriate linkers. For the prediction of an effective binding, molecular docking was carried out between the vaccine and immunological receptors (TLR8). Strong binding affinity and good docking scores clarified the stringency of the vaccines. Furthermore, molecular dynamics simulation was performed within the highest binding affinity complex to observe the stability, and minimize the designed vaccine's high mobility region to order to increase its stability. Then, Codon optimization and other physicochemical properties were performed to reveal that the vaccine would be suitable for a higher expression at cloning level and satisfactory thermostability condition. In conclusion, predicting the overall in silico assessment, we anticipated that our designed vaccine would be a plausible prevention against avian influenza A (H5N6) virus.

Phase 3 Randomized, Multicenter, Placebo-Controlled Study to Evaluate Safety, Immunogenicity, and Lot-to-Lot Consistency of an Adjuvanted Cell Culture-Derived, H5N1 Subunit Influenza Virus Vaccine in Healthy Adult Subjects

A cell-based process may be better suited for vaccine production during a highly pathogenic avian influenza (HPAI) pandemic. This was a phase 3, randomized, controlled, observer-blind, multicenter study evaluated safety, immunogenicity, and lot-to-lot consistency of two doses of a MF59-adjuvanted, H5N1 influenza pandemic vaccine manufactured on a cell culture platform (aH5N1c) in 3196 healthy adult subjects, stratified into two age groups: 18 to <65 and ≥65 years. Immunogenicity was measured using hemagglutination inhibition (HI) titers. HI antibody responses increased after the first aH5N1c vaccine dose, and 3 weeks after the second vaccination (Day 43), age-appropriate US Center for Biologics Evaluation and Research (CBER) and former European Medicines Authority Committee for Medicinal Products for Human Use (EMA CHMP) immunogenicity criteria were met. Six months after the first vaccination, HI titers were above baseline but no longer met CBER and CHMP criteria. No relevant changes over time were seen in placebo subjects. Solicited AEs were more frequent in the active treatment than the placebo group, primarily due to injection site pain. No serious adverse events (SAEs) related to aH5N1c- were reported. aH5N1c influenza vaccine elicited high levels of antibodies following two vaccinations administered 21 days apart and met both CBER and former CHMP immunogenicity criteria at Day 43 among both younger and older adults with a clinically acceptable safety profile. Consistency of the three consecutive aH5N1c vaccine lots was demonstrated (NCT02839330).

T cell mediated immunity against influenza H5N1 nucleoprotein, matrix and hemagglutinin derived epitopes in H5N1 survivors and non-H5N1 subjects

Background

Protection against the influenza virus by a specific antibody is relatively strain specific; meanwhile broader immunity may be conferred by cell-mediated immune response to the conserved epitopes across influenza virus subtypes. A universal broad-spectrum influenza vaccine which confronts not only seasonal influenza virus, but also avian influenza H5N1 virus is promising.

Methods

This study determined the specific and cross-reactive T cell responses against the highly pathogenic avian influenza A (H5N1) virus in four survivors and 33 non-H5N1 subjects including 10 H3N2 patients and 23 healthy individuals. Ex vivo IFN-γ ELISpot assay using overlapping peptides spanning the entire nucleoprotein (NP), matrix (M) and hemagglutinin (HA) derived from A/Thailand/1(KAN-1)/2004 (H5N1) virus was employed in adjunct with flow cytometry for determining T cell functions. Microneutralization (microNT) assay was performed to determine the status of previous H5N1 virus infection.

Results

IFN-γ ELISpot assay demonstrated that survivors nos. 1 and 2 had markedly higher T cell responses against H5N1 NP, M and HA epitopes than survivors nos. 3 and 4; and the magnitude of T cell responses against NP were higher than that of M and HA. Durability of the immunoreactivity persisted for as long as four years after disease onset. Upon stimulation by NP in IFN-γ ELISpot assay, 60% of H3N2 patients and 39% of healthy subjects exhibited a cross-reactive T cell response. The higher frequency and magnitude of responses in H3N2 patients may be due to blood collection at the convalescent phase of the patients. In H5N1 survivors, the effector peptide-specific T cells generated from bulk culture PBMCs by in vitro stimulation displayed a polyfunction by simultaneously producing IFN-γ and TNF-α, together with upregulation of CD107a in recognition of the target cells pulsed with peptide or infected with rVac-NP virus as investigated by flow cytometry.

Conclusions

This study provides an insight into the better understanding on the homosubtypic and heterosubtypic T cell-mediated immune responses in H5N1 survivors and non-H5N1 subjects. NP is an immunodominant target of cross-recognition owing to its high conservancy. Therefore, the development of vaccine targeting the conserved NP may be a novel strategy for influenza vaccine design.

Passive immunization with influenza haemagglutinin specific monoclonal antibodies

The isolation of broadly neutralising antibodies against the influenza haemagglutinin has spurred investigation into their clinical potential, and has led to advances in influenza virus biology and universal influenza vaccine development. Studies in animal models have been invaluable for demonstrating the prophylactic and therapeutic efficacy of broadly neutralising antibodies, for comparisons with antiviral drugs used as the standard of care, and for defining their mechanism of action and potential role in providing protection from airborne infection.

The persistence of multiple strains of avian influenza in live bird markets

Multiple subtypes of avian influenza (AI) and novel reassortants are frequently isolated from live bird markets (LBMs). However, our understanding of the drivers of persistence of multiple AI subtypes is limited. We propose a stochastic model of AI transmission within an LBM that incorporates market size, turnover rate and the balance of direct versus environmental transmissibility. We investigate the relationship between these factors and the critical community size (CCS) for the persistence of single and multiple AI strains within an LBM. We fit different models of seeding from farms to two-strain surveillance data collected from Shantou, China. For a single strain and plausible estimates for continuous turnover rates and transmissibility, the CCS was approximately 11 800 birds, only a 4.2% increase in this estimate was needed to ensure persistence of the co-infecting strains (two strains in a single host). Precise values of CCS estimates were sensitive to changes in market turnover rate and duration of the latent period. Assuming a gradual daily sell rate of birds the estimated CCS was higher than when an instantaneous selling rate was assumed. We were able to reproduce prevalence dynamics similar to observations from a single market in China with infection seeded every 5-15 days, and a maximum non-seeding duration of 80 days. Our findings suggest that persistence of co-infections is more likely to be owing to sequential infection of single strains rather than ongoing transmission of both strains concurrently. In any given system for a fixed set of ecological and epidemiological conditions, there is an LBM size below which the risk of sustained co-circulation is low and which may suggest a clear policy opportunity to reduce the frequency of influenza co-infection in poultry.

M2SR, a novel live influenza vaccine, protects mice and ferrets against highly pathogenic avian influenza

The emergence of highly pathogenic avian influenza H5N1 viruses has heightened global concern about the threat posed by pandemic influenza. To address the need for a highly effective universal influenza vaccine, we developed a novel M2-deficient single replication (M2SR) influenza vaccine virus and previously reported that it provided strong heterosubtypic protection against seasonal influenza viruses in mice. In the current study, we assessed M2SR induced protection against H5N1 influenza in mice and ferrets. Mice were intranasally inoculated with M2SR viruses containing the HA and NA from A/Vietnam/1203/2004 (M2SR H5N1) or A/California/07/2009 (M2SR H1N1). All M2SR vaccinated mice survived lethal challenge with influenza A/Vietnam/1203/2004 (H5N1), whereas 40% of mice vaccinated with recombinant H5 HA and none of the naïve controls survived. M2SR H5N1 provided sterile immunity, whereas low levels of virus were detected in the lungs of some M2SR H1N1 vaccinated mice. In contrast, recombinant H5 HA vaccinated mice and naïve controls showed systemic infection. M2SR H5N1 induced strong serum and mucosal antibody responses (IgG and IgA classes) against H5 HA, with high hemagglutination inhibition (HAI) titers. In contrast, while M2SR H1N1 elicited cross-reactive antibodies recognizing the H5 HA2 stalk region or the neuraminidase, no HAI activity against H5N1 virus was detected after M2SR H1N1 immunization. Both M2SR H5N1 and H1N1 also protected ferrets against lethal challenge with A/Vietnam/1203/2004. A prime-boost regimen provided optimal protection with no virus detected in the respiratory tract or brain after challenge. As in the mouse model, only the M2SR H5N1 vaccine induced HAI antibodies against the challenge virus in ferrets, while the M2SR H1N1 was able to provide protection without the induction of HAI antibodies. In summary, effective protection against highly pathogenic H5N1 influenza virus was provided by both homologous H5N1 M2SR and heterologous H1N1 M2SR demonstrating the cross-protective attributes of the M2SR platform.

A Perspective on the Structural and Functional Constraints for Immune Evasion: Insights from Influenza Virus

Influenza virus evolves rapidly to constantly escape from natural immunity. Most humoral immune responses to influenza virus target the hemagglutinin (HA) glycoprotein, which is the major antigen on the surface of the virus. The HA is composed of a globular head domain for receptor binding and a stem domain for membrane fusion. The major antigenic sites of HA are located in the globular head subdomain, which is highly tolerant of amino acid substitutions and continual addition of glycosylation sites. Nonetheless, the evolution of the receptor-binding site and the stem region on HA is severely constrained by their functional roles in engaging the host receptor and in mediating membrane fusion, respectively. Here, we review how broadly neutralizing antibodies (bnAbs) exploit these evolutionary constraints to protect against diverse influenza strains. We also discuss the emerging role of other epitopes that are conserved only in subsets of viruses. This rapidly increasing knowledge of the evolutionary biology, immunology, structural biology, and virology of influenza virus is invaluable for development and design of more universal influenza vaccines and novel therapeutics.

HAND HYGIENE PRACTICES POST EBOLA VIRUS DISEASE OUTBREAK IN A NIGERIAN TEACHING HOSPITAL

INTRODUCTION

Ebola virus disease (EVD) is a highly contagious viral infection that requires a high risk perception and practice of good hand hygiene by regular hand washing or use of hand sanitizers for infection control at all time. The declaration of Nigeria as an Ebola-free country by the World Health Organization on the 20th of October, 2014 has prompted many Nigerians, including healthcare workers, to discontinue the regular practice of good hand hygiene which was commonplace during the EVD outbreak.

OBJECTIVE

The study assessed hand hygiene practices for infection control after the West African Ebola virus disease outbreak in a Nigerian teaching hospital.

METHOD

This study was cross-sectional in design. A total of 450 staff of the University College Hospital, Ibadan participated in the survey. Data was collected using a structured, self-administered questionnaire. Chi-square test and multivariate logistic regression were used to determine associations between predictors of good hand hygiene practice at 5% level of significance.

RESULTS

The mean age was 42.2 ± 8.6 years. A higher proportion of respondents in this study had a good knowledge of the risk factors of EVD; good knowledge of the precautionary measures against EVD and a good risk perception towards EVD. However, the majority of respondents, 359 (80.0%), had a poor practice of hand hygiene for infection control. Having good knowledge of risk factors and precautionary measures against EVD was associated with practice of good hand hygiene. Respondents with good risk perception of EVD were 1.63 times more likely to practice good hand hygiene (OR= 1.63; 95% CI= 1.20 - 4.38; p= 0.019).

CONCLUSION

There was a good knowledge of risk factors and precautionary measures of EVD among staff of the University College Hospital, Ibadan. However, the majority of respondents had a poor practice of hand hygiene for infection control, Post EVD. Sensitization workshops to promote the regular practice of good hand hygiene is recommended for healthcare workers to control infection from EVD.

Intravenous Immunoglobulin Protects Against Severe Pandemic Influenza Infection

Influenza is a highly contagious, acute, febrile respiratory infection that can have fatal consequences particularly in individuals with chronic illnesses. Sporadic reports suggest that intravenous immunoglobulin (IVIg) may be efficacious in the influenza setting. We investigated the potential of human IVIg to ameliorate influenza infection in ferrets exposed to either the pandemic H1N1/09 virus (pH1N1) or highly pathogenic avian influenza (H5N1). IVIg administered at the time of influenza virus exposure led to a significant reduction in lung viral load following pH1N1 challenge. In the lethal H5N1 model, the majority of animals given IVIg survived challenge in a dose dependent manner. Protection was also afforded by purified F(ab′)₂ but not Fc fragments derived from IVIg, supporting a specific antibody-mediated mechanism of protection. We conclude that pre-pandemic IVIg can modulate serious influenza infection-associated mortality and morbidity. IVIg could be useful prophylactically in the event of a pandemic to protect vulnerable population groups and in the critical care setting as a first stage intervention.

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Intravenous immunoglobulin (IVIg), prepared prior to a pandemic, prevents pandemic influenza disease in ferrets.

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IVIg effectively reduced viral levels of pandemic H1N1 influenza and prevented disease due to avian influenza H5N1.

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This work has implications for preventing and treating pandemic influenza infections with IVIg before a vaccine is available.

Influenza pandemics cause large numbers of infections and deaths. There is a lag between the identification of a pandemic and the development of vaccines. Future pandemics may be caused by influenza strains resistant to current anti-influenza drugs. New treatments are needed for future pandemic influenza outbreaks. We show that a readily available product (intravenous immunoglobuling – pooled antibodies from human donors) can prevent viral replication and disease caused by 2 strains of pandemic influenza viruses (“swine-flu” and “bird-flu”) in an appropriate animal model of influenza. This could form the basis of future treatments for severe influenza caused by pandemic strains.

Weighing serological evidence of human exposure to animal influenza viruses - a literature review

Assessing influenza A virus strains circulating in animals and their potential to cross the species barrier and cause human infections is important to improve human influenza surveillance and preparedness. We reviewed studies describing serological evidence of human exposure to animal influenza viruses. Comparing serological data is difficult due to a lack of standardisation in study designs and in laboratory methods used in published reports. Therefore, we designed a scoring system to assess and weigh specificity of obtained serology results in the selected articles. Many studies report reliable evidence of antibodies to swine influenza viruses among persons occupationally exposed to pigs. Most avian influenza studies target H5, H7 and H9 subtypes and most serological evidence of human exposure to avian influenza viruses is reported for these subtypes. Avian influenza studies receiving a low grade in this review often reported higher seroprevalences in humans compared with studies with a high grade. Official surveillance systems mainly focus on avian H5 and H7 viruses. Swine influenza viruses and avian subtypes other than H5 and H7 (emphasising H9) should be additionally included in official surveillance systems. Surveillance efforts should also be directed towards understudied geographical areas, such as Africa and South America.

Antibody Persistence and Booster Responses to Split-Virion H5N1 Avian Influenza Vaccine in Young and Elderly Adults

Avian influenza continues to circulate and remains a global health threat not least because of the associated high mortality. In this study antibody persistence, booster vaccine response and cross-clade immune response between two influenza A(H5N1) vaccines were compared. Participants aged over 18-years who had previously been immunized with a clade 1, A/Vietnam vaccine were re-immunized at 6-months with 7.5 μg of the homologous strain or at 22-months with a clade 2, alum-adjuvanted, A/Indonesia vaccine. Blood sampled at 6, 15 and 22-months after the primary course was used to assess antibody persistence. Antibody concentrations 6-months after primary immunisation with either A/Vietnam vaccine 30 μg alum-adjuvanted vaccine or 7.5 μg dose vaccine were lower than 21-days after the primary course and waned further with time. Re-immunization with the clade 2, 30 μg alum-adjuvanted vaccine confirmed cross-clade reactogenicity. Antibody cross-reactivity between A(H5N1) clades suggests that in principle a prime-boost vaccination strategy may provide both early protection at the start of a pandemic and improved antibody responses to specific vaccination once available.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00415129.

Safety and persistence of the humoral and cellular immune responses induced by 2 doses of an AS03-adjuvanted A(H1N1)pdm09 pandemic influenza vaccine administered to infants, children and adolescents: Two open, uncontrolled studies

In children, 2 AS03-adjuvanted A(H1N1)pdm09 vaccine doses given 21 days apart were previously shown to induce a high humoral immune response and to have an acceptable safety profile up to 42 days following the first vaccination. Here, we analyzed the persistence data from 2 open-label studies, which assessed the safety, and humoral and cell-mediated immune responses induced by 2 doses of this vaccine. The first study was a phase II, randomized trial conducted in 104 children aged 6–35 months vaccinated with the A(H1N1)pdm09 vaccine containing 1.9 µg haemagglutinin antigen (HA) and AS03_B (5.93 mg tocopherol) and the second study, a phase III, non-randomized trial conducted in 210 children and adolescents aged 3–17 years vaccinated with the A(H1N1)pdm09 vaccine containing 3.75 µg HA and AS03_A (11.86 mg tocopherol). Approximately one year after the first dose, all children with available data were seropositive for haemagglutinin inhibition and neutralising antibody titres, but a decline in geometric mean antibody titres was noted. The vaccine induced a cell-mediated immune response in terms of antigen-specific CD4⁺ T-cells, which persisted up to one year post-vaccination. The vaccine did not raise any safety concern, though these trials were not designed to detect rare events. In conclusion, 2 doses of the AS03-adjuvanted A(H1N1)pdm09 vaccine at 2 different dosages had a clinically acceptable safety profile, and induced high and persistent humoral and cell-mediated immune responses in children aged 6–35 months and 3–17 years. These studies have been registered at www.clinicaltrials.gov NCT00971321 and NCT00964158.

A novel M2e-multiple antigenic peptide providing heterologous protection in mice

Swine influenza viruses (SwIVs) cause considerable morbidity and mortality in domestic pigs, resulting in a significant economic burden. Moreover, pigs have been considered to be a possible mixing vessel in which novel strains loom. Here, we developed and evaluated a novel M2e-multiple antigenic peptide (M2e-MAP) as a supplemental antigen for inactivated H3N2 vaccine to provide cross-protection against two main subtypes of SwIVs, H1N1 and H3N2. The novel tetra-branched MAP was constructed by fusing four copies of M2e to one copy of foreign T helper cell epitopes. A high-yield reassortant H3N2 virus was generated by plasmid based reverse genetics. The efficacy of the novel H3N2 inactivated vaccines with or without M2e-MAP supplementation was evaluated in a mouse model. M2e-MAP conjugated vaccine induced strong antibody responses in mice. Complete protection against the heterologous swine H1N1 virus was observed in mice vaccinated with M2e-MAP combined vaccine. Moreover, this novel peptide confers protection against lethal challenge of A/Puerto Rico/8/34 (H1N1). Taken together, our results suggest the combined immunization of reassortant inactivated H3N2 vaccine and the novel M2e-MAP provided cross-protection against swine and human viruses and may serve as a promising approach for influenza vaccine development.

Cross-reactivity between avian influenza A (H7N9) virus and divergent H7 subtypic- and heterosubtypic influenza A viruses

The number of human avian H7N9 influenza infections has been increasing in China. Understanding their antigenic and serologic relationships is crucial for developing diagnostic tools and vaccines. Here, we evaluated the cross-reactivities and neutralizing activities among H7 subtype influenza viruses and between H7N9 and heterosubtype influenza A viruses. We found strong cross-reactivities between H7N9 and divergent H7 subtypic viruses, including H7N2, H7N3, and H7N7. Antisera against H7N2, H7N3, and H7N7 could also effectively neutralize two distinct H7N9 strains. Two-way cross-reactivities exist within group 2, including H3 and H4, whereas one-way cross-reactivities were found across other groups, including H1, H10, H9, and H13. Our data indicate that the hemaglutinins from divergent H7 subtypes may facilitate the development of vaccines for distinct H7N9 infections. Moreover, serologic diagnoses for H7N9 infections need to consider possible interference from the cross-reactivity of H7N9 with other subtype influenza viruses.

Protection against H5N1 by multiple immunizations with seasonal influenza vaccine in mice is correlated with H5 cross-reactive antibodies

BACKGROUND

Current seasonal influenza vaccines are believed to confer protection against a narrow range of virus strains. However, their protective ability is commonly estimated based on an in vitro correlate of protection that only considers a subset of anti-influenza antibodies that are typically strain specific, i.e., hemagglutination inhibiting antibodies. Here, we evaluate the breadth of protection induced with a seasonal trivalent influenza vaccine (composition H1N1 A/California/07/09, H3N2 A/Victoria/210/08, B/Brisbane/60/08) against influenza challenge in mice.

METHODS

Balb/c mice were immunized once, twice, or three times with seasonal influenza vaccine to assess protection against heterosubtypic H5N1 influenza challenge, or homologous H1N1 influenza virus as a control. Passive transfer of immune serum was used to determine the contribution of humoral immunity to protection.

RESULTS

Multiple immunizations with seasonal influenza vaccine induced up to 80% protection against heterosubtypic H5N1 influenza challenge in mice without eliciting detectable H5N1 neutralizing antibodies. Comparable levels of protection were reached by passive transfer of immune serum, and protection was correlated with the titer of vaccine-induced, H5 cross-reactive, non-neutralizing antibodies that are at least in part directed against conserved HA epitopes.

CONCLUSIONS

Here, we demonstrate that seasonal vaccine has the ability to induce broad serum-mediated protection, and that the mechanism of this protection is different from the vaccine-induced homologous protection.

The safety and immunogenicity of a MF59-adjuvanted H5N1 prepandemic influenza vaccine in healthy adults primed with homologous or heterologous H5N1 vaccines: an observational study

Background

World Health Organization (WHO) has recommended individuals with increased risk of contracting influenza A H5N1 infection to be immunized against the virus during the inter-pandemic period. Safety and immunogenicity of H5N1 vaccine among participants primed with homologous or heterologous H5N1 vaccines produced by diverse manufactures have not been reported.

Methods

Healthy individuals aged 20 to 60 years old were recruited and stratified into three groups: participants without priming (control group), participants primed with A/Indonesia/05/2005 vaccine, participants primed with A/Vietnam/1194/2004 vaccine and A/Indonesia/05/2005 vaccine. Enrolled participants received two doses of MF59-adjuvanted A/Vietnam/1194/2004 vaccine (study vaccine). Solicited reactions were recorded by vaccine recipients. Blood samples were obtained for hemagglutination inhibition test.

Results

A total of 131 participants were enrolled. No significant adverse events were recorded. Tenderness, fatigue and general muscle ache were the most common solicited reactions which alleviated within one week of immunization. Three weeks after two doses of the study vaccine, 63%, 68% and 88% were in seroprotective status in the control group, A/Indonesia/05/2005 primed group and A/Vietnam/1194/2004 and A/Indonesia/05/2005 primed group, respectively. Participants primed with A/Vietnam/1194/2004 and A/Indonesia/05/2005 showed high immune response after booster with one dose of the study vaccine.

Conclusion

The study vaccine did not cause severe adverse events. It elicited mostly mild to moderate reactions among participants. Participants primed with A/Vietnam/1194/2004 and A/Indonesia/05/2005 vaccine showed higher immune response than those without priming or primed with A/Indonesia/05/2005 vaccine. The report suggested those with an increased risk of influenza A H5N1 virus exposure may benefit from receiving influenza A H5N1 priming during the inter-pandemic period if the antigenicity of the pandemic influenza strain is similar to that of the priming strain.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-014-0587-z) contains supplementary material, which is available to authorized users.

Cellular and humoral cross-immunity against two H3N2v influenza strains in presumably unexposed healthy and HIV-infected subjects

Human cases of infection due to a novel swine-origin variant of influenza A virus subtype H3N2 (H3N2v) have recently been identified in the United States. Pre-existing humoral and cellular immunity has been recognized as one of the key factors in limiting the infection burden of an emerging influenza virus strain, contributing to restrict its circulation and to mitigate clinical presentation. Aim of this study was to assess humoral and cell-mediated cross immune responses to H3N2v in immuno-competent (healthy donors, n = 45) and immuno-compromised hosts (HIV-infected subjects, n = 46) never exposed to H3N2v influenza strain. Humoral response against i) H3N2v (A/H3N2/Ind/08/11), ii) animal vaccine H3N2 strain (A/H3N2/Min/11/10), and iii) pandemic H1N1 virus (A/H1N1/Cal/07/09) was analysed by hemagglutination inhibition assay; cell-mediated response against the same influenza strains was analysed by ELISpot assay. A large proportion of healthy and HIV subjects displayed cross-reacting humoral and cellular immune responses against two H3N2v strains, suggesting the presence of B- and T-cell clones able to recognize epitopes from emerging viral strains in both groups. Specifically, humoral response was lower in HIV subjects than in HD, and a specific age-related pattern of antibody response against different influenza strains was observed both in HD and in HIV. Cellular immune response was similar between HD and HIV groups and no relationship with age was reported. Finally, no correlation between humoral and cellular immune response was observed. Overall, a high prevalence of HD and HIV patients showing cross reactive immunity against two H3N2v strains was observed, with a slightly lower proportion in HIV persons. Other studies focused on HIV subjects at different stages of diseases are needed in order to define how cross immunity can be affected by advanced immunosuppression.

Cross-reactive influenza-specific antibody-dependent cellular cytotoxicity in intravenous immunoglobulin as a potential therapeutic against emerging influenza viruses

BACKGROUND

Intravenous immunoglobulin (IVIG) is a purified pool of human antibodies from thousands of donors that is used to prevent or treat primary immune deficiency, several infectious diseases, and autoimmune diseases. The antibodies that mediate antibody-dependent cellular cytotoxicity (ADCC) against heterologous influenza strains may be present in IVIG preparations.

METHODS

We tested 8 IVIG preparations prior to the 2009 H1N1 swine-origin influenza pandemic and 10 IVIG preparations made after 2010 for their ability to mediate influenza-specific ADCC.

RESULTS

ADCC mediating antibodies to A(H1N1)pdm09 hemagglutinin (HA) and neuraminidase (NA) were detected in IVIG preparations prior to the 2009-H1N1 pandemic. The HA-specific ADCC targeted both the HA1 and HA2 regions of A(H1N1)pdm09 HA and was capable of recognizing a broad range of HA proteins including those from recent avian influenza strains A(H5N1) and A(H7N9). The low but detectable ADCC recognition of A(H7N9) was likely due to rare individuals in the population contributing cross-reactive antibodies to IVIG.

CONCLUSIONS

IVIG preparations contain broadly cross-reactive ADCC mediating antibodies. IVIG may provide at least some level of protection for individuals at high risk of severe influenza disease, especially during influenza pandemics prior to the development of effective vaccines.

The antigenic architecture of the hemagglutinin of influenza H5N1 viruses

Human infection with the highly pathogenic avian influenza A virus H5N1 is associated with a high mortality and morbidity. H5N1 continues to transmit from poultry to the human population, raising serious concerns about its pandemic potential. Current influenza H5N1 vaccines are based upon the elicitation of a neutralizing antibody (Ab) response against the major epitope regions of the viral surface glycoprotein, hemagglutinin (HA). However, antigenic drift mutations in immune-dominant regions on the HA structure allow the virus to escape Ab neutralization. Epitope mapping using neutralizing monoclonal antibodies (mAb) helps define mechanisms of antigenic drift, neutralizing escape and can facilitate pre-pandemic vaccine design. This review explores the current knowledge base of the antigenic sites of the H5N1 HA molecule. The relationship between the epitope architecture of the H5N1 HA, antigenic evolution of the different H5N1 lineages and the antigenic complexity of the H5N1 virus lineages that constitute potential pandemic strains are discussed in detail.

Selection of an adjuvant for seasonal influenza vaccine in elderly people: modelling immunogenicity from a randomized trial

Background

Improved influenza vaccines are needed to reduce influenza-associated complications in older adults. The aim of this study was to identify the optimal formulation of adjuvanted seasonal influenza vaccine for use in elderly people.

Methods

This observer-blind, randomized study assessed the optimal formulation of adjuvanted seasonal influenza vaccine based on immunogenicity and safety in participants aged ≥65 years. Participants were randomized (~200 per group) to receive one dose of non-adjuvanted vaccine or one of eight formulations of vaccine formulated with a squalene and tocopherol oil-in-water emulsion-based Adjuvant System (AS03_C, AS03_B or AS03_A, with 2.97, 5.93 and 11.86 mg tocopherol, respectively) together with the immunostimulant monophosphoryl lipid A (MPL, doses of 0, 25 or 50 mg). Hemagglutination-inhibition (HI) antibody responses and T-cell responses were assessed on Day 0 and 21 days post-vaccination. The ratio of HI-based geometric mean titers in adjuvanted versus non-adjuvanted vaccine groups were calculated and the lower limit of the 90% confidence interval was transformed into a desirability index (a value between 0 and 1) in an experimental domain for each vaccine strain, and plotted in relation to the AS03 and MPL dose combination in the formulation. This model was used to assess the optimal formulation based on HI antibody titers. Reactogenicity and safety were also assessed. The immunogenicity and safety analyses were used to evaluate the optimal formulation of adjuvanted vaccine.

Results

In the HI antibody-based model, an AS03 dose–response was evident; responses against the A/H1N1 and A/H3N2 strains were higher for all adjuvanted formulations versus non-adjuvanted vaccine, and for the AS03_A-MPL25, AS03_B-MPL25 and AS03_B-MPL50 formulations against the B strain. Modelling using more stringent criteria (post hoc) showed a clear dose-range effect for the AS03 component against all strains, whereas MPL showed a limited effect. Higher T-cell responses for adjuvanted versus non-adjuvanted vaccine were observed for all except two formulations (AS03_C and AS03_B-MPL25). Reactogenicity increased with increasing AS03 dosage, and with MPL. No safety concerns were raised.

Conclusions

Five formulations containing AS03_A or AS03_B were identified as potential candidates to improve immune responses to influenza vaccination; AS03_B without MPL showed the best balance between improved immunogenicity and acceptable reactogenicity.

Trial registration

This trial is registered at ClinicalTrials.gov, NCT00540592

Immune responses to infection with H5N1 influenza virus

Influenza A H5N1 viruses remain a substantial threat to global public health. In particular, the expanding genetic diversity of H5N1 viruses and the associated risk for human adaptation underscore the importance of better understanding host immune responses that may protect against disease or infection. Although much emphasis has been placed on investigating early virus-host interactions and the induction of innate immune responses, little is known of the consequent adaptive immune response to H5N1 virus infection. In this review, we describe the H5N1 virus-specific and cross-reactive antibody and T cell responses in humans and animal models. Data from limited studies suggest that although initially robust, there is substantial waning of the serum antibody responses in survivors of H5N1 virus infection. Characterization of monoclonal antibodies generated from memory B cells of survivors of H5N1 virus infection has provided an understanding of the fine specificity of the human antibody response to H5N1 virus infection and identified strategies for immunotherapy. Human T cell responses induced by infection with seasonal influenza viruses are directed to relatively conserved internal proteins and cross-react with the H5N1 subtype. A role for T cell-based heterosubtypic immunity against H5N1 viruses is suggested in animal studies. Further studies on adaptive immune responses to H5N1 virus infection in both humans and animals are needed to inform the design of optimal immunological treatment and prevention modalities.

Population-level antibody estimates to novel influenza A/H7N9

There are no contemporary data available describing human immunity to novel influenza A/H7N9. Using 1723 prospectively collected serum samples in southern Vietnam, we tested for antibodies to 5 avian influenza virus antigens, using a protein microarray. General-population antibody titers against subtype H7 virus are higher than antibody titers against subtype H5 and lower than titers against H9. The highest titers were observed for human influenza virus subtypes. Titers to avian influenza virus antigens increased with age and with geometric mean antibody titer to human influenza virus antigens. There were no titer differences between the urban and the rural location in our study.

Evaluation of in vitro cross-reactivity to avian H5N1 and pandemic H1N1 2009 influenza following prime boost regimens of seasonal influenza vaccination in healthy human subjects: a randomised trial

Introduction

Recent studies have demonstrated that inactivated seasonal influenza vaccines (IIV) may elicit production of heterosubtypic antibodies, which can neutralize avian H5N1 virus in a small proportion of subjects. We hypothesized that prime boost regimens of live and inactivated trivalent seasonal influenza vaccines (LAIV and IIV) would enhance production of heterosubtypic immunity and provide evidence of cross-protection against other influenza viruses.

Methods

In an open-label study, 26 adult volunteers were randomized to receive one of four vaccine regimens containing two doses of 2009-10 seasonal influenza vaccines administered 8 (±1) weeks apart: 2 doses of LAIV; 2 doses of IIV; LAIV then IIV; IIV then LAIV. Humoral immunity assays for avian H5N1, 2009 pandemic H1N1 (pH1N1), and seasonal vaccine strains were performed on blood collected pre-vaccine and 2 and 4 weeks later. The percentage of cytokine-producing T-cells was compared with baseline 14 days after each dose.

Results

Subjects receiving IIV had prompt serological responses to vaccine strains. Two subjects receiving heterologous prime boost regimens had enhanced haemagglutination inhibition (HI) and neutralization (NT) titres against pH1N1, and one subject against avian H5N1; all three had pre-existing cross-reactive antibodies detected at baseline. Significantly elevated titres to H5N1 and pH1N1 by neuraminidase inhibition (NI) assay were observed following LAIV-IIV administration. Both vaccines elicited cross-reactive CD4+ T-cell responses to nucleoprotein of avian H5N1 and pH1N1. All regimens were safe and well tolerated.

Conclusion

Neither homologous nor heterologous prime boost immunization enhanced serum HI and NT titres to 2009 pH1N1 or avian H5N1 compared to single dose vaccine. However heterologous prime-boost vaccination did lead to in vitro evidence of cross-reactivity by NI; the significance of this finding is unclear. These data support the strategy of administering single dose trivalent seasonal influenza vaccine at the outset of an influenza pandemic while a specific vaccine is being developed.

Trial Registration

ClinicalTrials.gov NCT01044095

Evidence that life history characteristics of wild birds influence infection and exposure to influenza A viruses

We report on life history characteristics, temporal, and age-related effects influencing the frequency of occurrence of avian influenza (AI) viruses in four species of migratory geese breeding on the Yukon-Kuskokwim Delta, Alaska. Emperor geese (Chen canagica), cackling geese (Branta hutchinsii), greater white-fronted geese (Anser albifrons), and black brant (Branta bernicla), were all tested for active infection of AI viruses upon arrival in early May, during nesting in June, and while molting in July and August, 2006–2010 (n = 14,323). Additionally, prior exposure to AI viruses was assessed via prevalence of antibodies from sera samples collected during late summer in 2009 and 2010. Results suggest that geese are uncommonly infected by low pathogenic AI viruses while in Alaska. The percent of birds actively shedding AI viruses varied annually, and was highest in 2006 and 2010 (1–3%) and lowest in 2007, 2008, and 2009 (<0.70%). Contrary to findings in ducks, the highest incidence of infected birds was in late spring when birds first arrived from staging and wintering areas. Despite low prevalence, most geese were previously exposed to AI viruses, as indicated by high levels of seroprevalence during late summer (47%–96% across species; n = 541). Seroprevalence was >95% for emperor geese, a species that spends part of its life cycle in Asia and is endemic to Alaska and the Bering Sea region, compared to 40–60% for the other three species, whose entire life cycles are within the western hemisphere. Birds <45 days of age showed little past exposure to AI viruses, although antibodies were detected in samples from 5-week old birds in 2009. Seroprevalence of known age black brant revealed that no birds <4 years old had seroconverted, compared to 49% of birds ≥4 years of age.

Profiling of humoral response to influenza A(H1N1)pdm09 infection and vaccination measured by a protein microarray in persons with and without history of seasonal vaccination

BACKGROUND

The influence of prior seasonal influenza vaccination on the antibody response produced by natural infection or vaccination is not well understood.

METHODS

We compared the profiles of antibody responses of 32 naturally infected subjects and 98 subjects vaccinated with a 2009 influenza A(H1N1) monovalent MF59-adjuvanted vaccine (Focetria, Novartis), with and without a history of seasonal influenza vaccination. Antibodies were measured by hemagglutination inhibition (HI) assay for influenza A(H1N1)pdm09 and by protein microarray (PA) using the HA1 subunit for seven recent and historic H1, H2 and H3 influenza viruses, and three avian influenza viruses. Serum samples for the infection group were taken at the moment of collection of the diagnostic sample, 10 days and 30 days after onset of influenza symptoms. For the vaccination group, samples were drawn at baseline, 3 weeks after the first vaccination and 5 weeks after the second vaccination.

RESULTS

We showed that subjects with a history of seasonal vaccination generally exhibited higher baseline titers for the various HA1 antigens than subjects without a seasonal vaccination history. Infection and pandemic influenza vaccination responses in persons with a history of seasonal vaccination were skewed towards historic antigens.

CONCLUSIONS

Seasonal vaccination is of significant influence on the antibody response to subsequent infection and vaccination, and further research is needed to understand the effect of annual vaccination on protective immunity.

Broadly neutralizing antiviral antibodies

A fascinating aspect of viral evolution relates to the ability of viruses to escape the adaptive immune response. The widely held view has been that the great variability of viral glycoproteins would be an absolute obstacle to the development of antibody-based therapies or vaccines that could confer broad and long-lasting protection. In the past five years, new approaches have been developed to interrogate human memory B cells and plasma cells with high efficiency and to isolate several broadly neutralizing antiviral antibodies against highly variable pathogens such as HIV-1 and influenza virus. These antibodies not only provide new tools for prophylaxis and therapy for viral diseases but also identify conserved epitopes that may be used to design new vaccines capable of conferring broader protection.

Neuraminidase-inhibiting antibody is a correlate of cross-protection against lethal H5N1 influenza virus in ferrets immunized with seasonal influenza vaccine

In preparing for the threat of a pandemic of avian H5N1 influenza virus, we need to consider the significant delay (4 to 6 months) necessary to produce a strain-matched vaccine. As some degree of cross-reactivity between seasonal influenza vaccines and H5N1 virus has been reported, this was further explored in the ferret model to determine the targets of protective immunity. Ferrets were vaccinated with two intramuscular inoculations of trivalent inactivated split influenza vaccine or subcomponent vaccines, with and without adjuvant, and later challenged with a lethal dose of A/Vietnam/1203/2004 (H5N1) influenza virus. We confirmed that vaccination with seasonal influenza vaccine afforded partial protection against lethal H5N1 challenge and showed that use of either AlPO(4) or Iscomatrix adjuvant with the vaccine resulted in complete protection against disease and death. The protection was due exclusively to the H1N1 vaccine component, and although the hemagglutinin contributed to protection, the dominant protective response was targeted toward the neuraminidase (NA) and correlated with sialic acid cleavage-inhibiting antibody titers. Purified heterologous NA formulated with Iscomatrix adjuvant was also protective. These results suggest that adjuvanted seasonal trivalent vaccine could be used as an interim measure to decrease morbidity and mortality from H5N1 prior to the availability of a specific vaccine. The data also highlight that an inducer of cross-protective immunity is the NA, a protein whose levels are not normally monitored in vaccines and whose capacity to induce immunity in recipients is not normally assessed.

Influenza A virus nucleoprotein derived from Escherichia coli or recombinant vaccinia (Tiantan) virus elicits robust cross-protection in mice

BACKGROUND

Immunity to conserved viral antigens is an attractive approach to develop a universal vaccine against epidemic and pandemic influenza. A nucleoprotein (NP)-based vaccine has been explored and preliminary studies have shown promise. However, no study has explored the immunity and cross-protective efficacy of recombinant NP derived from Escherichia coli compared with recombinant vaccinia virus (Tiantan).

METHODS

Recombinant NP protein (rNP) from influenza virus A/Jingke/30/95(H3N2) was obtained from E. coli and recombinant vaccinia virus (Tiantan) RVJ1175NP. Purified rNP without adjuvant and RVJ1175NP were used to immunize BALB/c mice intramuscularly. Humoral immune responses were detected by ELISA, while cell-mediated immune responses were measured by ex vivo IFN-γ ELISPOT and in vivo cytotoxicity assays. The cross-protective efficacy was assessed by a challenge with a heterosubtype of influenza virus A/PR/8/34(H1N1).

RESULTS

Our results demonstrate that a high dose (90 μg) of rNP induced NP-specific antibodies and T cell responses that were comparable with those of RVJ1175NP in mice. Importantly, the survival ratio (36, 73, and 78%) of the vaccinated mice after the influenza virus A/PR/8/34(H1N1) challenge was rNP vaccine dose-dependent (10, 30, and 90 μg, respectively), and no significant differences were observed between the rNP- and RVJ1175NP-immunized (91%) mice.

CONCLUSIONS

Influenza A virus NP derived from E. coli or recombinant vaccinia (Tiantan) virus elicited cross-protection against influenza virus in mice, and the immune response and protective efficacy of rNP were comparable to RVJ1175NP. These data provide a basis for the use of prokaryotically expressed NP as a candidate universal influenza vaccine.

Cellular and humoral immune responses to pandemic influenza vaccine in healthy and in highly active antiretroviral therapy-treated HIV patients

Influenza vaccination is recommended for HAART-treated HIV patients to prevent influenza illness and complications. Due to the known ability of T cells to mediate a broadly cross-reactive response, vaccination effectiveness in cell-mediated immune (CMI) response induction is a main objective in new influenza vaccination strategies. Nevertheless, data on CMI responses after pandemic vaccination in HIV subjects are still missing. In the present study, the ability of a single dose of adjuvanted pandemic influenza vaccine to induce humoral and CMI responses was compared in HAART-treated HIV patients and in healthcare workers. Healthcare workers (HCW, n=65) and HAART-treated HIV patients (HIV, n=67) receiving pandemic vaccination were enrolled and analyzed before (t0) and after (t1) vaccination. The analysis of strain-specific humoral response was performed by HAI assay; CMI against pandemic (A/H1N1/Cal/09) and seasonal (A/H1N1/Brisb/07 and A/H3N2/Brisb/07) strains was analyzed by ELISpot and intracellular staining followed by flow cytometry. Pandemic vaccination was effective in inducing both humoral and cell-mediated responses in HAART-treated HIV patients as well as in HCWs. A large fraction of both HCWs and HIV-infected patients showed a T cell response to the pandemic strain before vaccination, suggesting possible previous exposure to A/H1N1/pdm/09 and/or cross-reactive T cells. Notably, pandemic vaccine was also able to boost cross-reactive immune responses to seasonal strains. Finally, a weaker boost of both strain-specific and cross-reactive T cell immunity was found in individuals showing a higher baseline response. These data show the effectiveness of adjuvanted pandemic vaccine to induce both humoral and cellular (strain-specific and cross-reactive) immune responses in HIV patients similar to HCWs.

Aflunov®: a vaccine tailored for pre-pandemic and pandemic approaches against influenza

INTRODUCTION

Aflunov is an egg-derived, subunit vaccine from Novartis Vaccines and Diagnostics containing 7.5 μg of hemagglutinin (HA) from the avian A/H5N1 virus and the oil-in-water adjuvant MF59.

AREAS COVERED

Aflunov behaves as a pre-pandemic vaccine. It has a good safety profile at all ages. At all ages, it induces high and persisting antibody titers and activation of HA-specific Th0/Th1 CD4(+) T cells, the levels of which correlate with the neutralizing antibody titers after a booster dose 6 months later. Aflunov triggers strong immunological memory, which persists for at least 6 - 8 years and can be rapidly boosted with a heterovariant vaccine strain, inducing very high neutralizing antibody titers within one week. These antibodies broadly and strongly cross-react with drifted H5N1 virus strains from various clades. Finally, the MF59 changes the pattern of HA recognition by antibodies that react with the HA1 more than with the HA2 region.

EXPERT OPINION

The available data show that Aflunov is a pre-pandemic vaccine suitable not only for stockpiling in case of a pandemic, but also before a pandemic is declared, with the ultimate objective of preventing the onset of an influenza pandemic.

Seroconversion to seasonal influenza viruses after A(H1N1)pdm09 virus infection, Quebec, Canada

We looked for cross-reactive antibodies in 122 persons with paired serum samples collected during the 2009 pandemic of influenza virus A(H1N1)pdm09. Eight (12%) of 67 persons with A(H1N1)pdm09 infection confirmed by reverse transcription PCR and/or serology also seroconverted to the seasonal A/Brisbane/59/2007 (H1N1) virus, compared with 1 (2%) of 55 A(H1N1)pdm09-negative persons (p<0.05).

Contribution of antibody production against neuraminidase to the protection afforded by influenza vaccines

Vaccines are instrumental in controlling the burden of influenza virus infection in humans and animals. Antibodies raised against both major viral surface glycoproteins, hemagglutinin (HA) and neuraminidase (NA), can contribute to protective immunity. Vaccine-induced HA antibodies have been characterized extensively, and they generally confer protection by blocking the attachment and fusion of a homologous virus onto host cells. Although not as well characterized, some functions of NA antibodies in influenza vaccine-mediated immunity have been recognized for many years. In this review, we summarize the case for NA antibodies in influenza vaccine-mediated immunity. In the absence of well-matched HA antibodies, NA antibodies can provide varying degrees of protection against disease. NA proteins of seasonal influenza vaccines have been shown in some instances to elicit serum antibodies with cross-reactivity to avian-origin and swine-origin influenza strains, in addition to HA drift variants. NA-mediated immunity has been linked to (i) conserved NA epitopes amongst otherwise antigenically distinct strains, partly attributable to the segmented influenza viral genome; (ii) inhibition of NA enzymatic activity; and (iii) the NA content in vaccine formulations. There is a potential to enhance the effectiveness of existing and future influenza vaccines by focusing greater attention on the antigenic characteristics and potency of the NA protein.

Evaluation of the sublingual route for administration of influenza H5N1 virosomes in combination with the bacterial second messenger c-di-GMP

Avian influenza A H5N1 is a virus with pandemic potential. Mucosal vaccines are attractive as they have the potential to block viruses at the site of entry, thereby preventing both disease and further transmission. The intranasal route is safe for the administration of seasonal live-attenuated influenza vaccines, but may be less suitable for administration of pandemic vaccines. Research into novel mucosal routes is therefore needed. In this study, a murine model was used to compare sublingual administration with intranasal and intramuscular administration of influenza H5N1 virosomes (2 µg haemagglutinin; HA) in combination with the mucosal adjuvant (3′,5′)-cyclic dimeric guanylic acid (c-di-GMP). We found that sublingual immunisation effectively induced local and systemic H5N1-specific humoral and cellular immune responses but that the magnitude of response was lower than after intranasal administration. However, both the mucosal routes were superior to intramuscular immunisation for induction of local humoral and systemic cellular immune responses including high frequencies of splenic H5N1-specific multifunctional (IL-2⁺TNF-α⁺) CD4⁺ T cells. The c-di-GMP adjuvanted vaccine elicited systemic haemagglutination inhibition (HI) antibody responses (geometric mean titres ≥40) both when administered sublingually, intranasally and inramuscularly. In addition, salivary HI antibodies were elicited by mucosal, but not intramuscular vaccination. We conclude that the sublingual route is an attractive alternative for administration of pandemic influenza vaccines.

Dose-sparing H5N1 A/Indonesia/05/2005 pre-pandemic influenza vaccine in adults and elderly adults: a phase III, placebo-controlled, randomized study

BACKGROUND

Highly pathogenic avian influenza H5N1 viruses remain a threat to human health, with potential to become pandemic agents.

METHODS

This phase III, placebo-controlled, observer-blinded study evaluated the immunogenicity, cross-reactivity, safety, and lot consistency of 2 doses of oil-in-water (AS03(A)) adjuvanted H5N1 A/Indonesia/05/2005 (3.75 μg hemagglutinin antigen) prepandemic candidate vaccine in 4561 adults aged 18-91 years.

RESULTS

Humoral antibody responses in the H5N1 vaccine groups fulfilled US and European immunogenicity licensure criteria for pandemic vaccines in all age strata 21 days after the second dose. At 6 months after the administration of the primary dose, serum antibody seroconversion rates continued to fulfill licensure criteria. Neutralizing cross-clade immune responses were demonstrated against clade 1 A/Vietnam/1194/2004. Consistency was demonstrated for 3 consecutive H5N1 vaccine lots. Temporary injection-site pain was more frequent with H5N1 vaccine than placebo (89.3% and 70.7% in the 18-64 and ≥65 years strata vs 22.2% and 14.4% in the placebo groups). Unsolicited adverse event frequency, including medically attended and serious events, was similar between groups through day 364.

CONCLUSIONS

In adults and elderly adults, AS03(A)-adjuvanted H5N1 candidate vaccine was highly immunogenic for A/Indonesia/05/2005, with cross-reactivity against A/Vietnam/1194/2004. Temporary injection site reactions were more frequent with H5N1 vaccine than placebo, although the H5N1 vaccine was well tolerated overall. Clinical Trials Registration. NCT00616928.

Immunogenicity profile of a 3.75-μg hemagglutinin pandemic rH5N1 split virion AS03A-adjuvanted vaccine in elderly persons: a randomized trial

Background. Elderly persons often experience a reduced immune response to influenza vaccination. We evaluated the usual dose of AS03_A-adjuvanted H5N1 pandemic vaccine (3.75 μg hemagglutinin of A/Vietnam/1194/2004-like strain) compared with a double dose in an elderly population.

Methods. This phase 2, open-label study (NCT00397215; http://www.clinicaltrials.gov) randomized participants (age, ≥61 years) to receive, on days 0 and 21: (1) a single dose of AS03_A-adjuvanted vaccine (n = 152), (2) a single dose of nonadjuvanted vaccine (n = 54), (3) a double dose of AS03_A-adjuvanted vaccine (n = 145), or (4) a double dose of nonadjuvanted vaccine (n = 44). The primary end point was hemagglutination inhibition (HI) and neutralizing antibody response against vaccine antigen (according-to-protocol cohort).

Results. Day 42 geometric mean titers for HI antibodies were 126.8 and 237.3 for single and double doses of the AS03_A-adjuvanted vaccine, respectively. Corresponding values for neutralizing antibodies were 447.3 and 595.8. Although the immune response was higher with the double dose, European Committee for Human Medicinal Products criteria for seroconversion and seroprotection rates were achieved in both AS03_A-adjuvanted groups. Antigen-specific CD4 T cell responses were elicited. Immune response persistence at 6 months was high. Immune response in the non-adjuvanted groups was considerably less.

Conclusions. The AS03_A-adjuvanted H5N1 vaccine can be administered elderly persons at the same dose and schedule as in younger adults.

Seasoned adaptive antibody immunity for highly pathogenic pandemic influenza in humans

Fundamentally new approaches are required for the development of vaccines to pre-empt and protect against emerging and pandemic influenzas. Current strategies involve post-emergent homotypic vaccines that are modelled upon select circulating 'seasonal' influenzas, but cannot induce cross-strain protection against newly evolved or zoonotically introduced highly pathogenic influenza (HPI). Avian H5N1 and the less-lethal 2009 H1N1 and their reassortants loom as candidates to seed a future HPI pandemic. Therefore, more universal 'seasoned' vaccine approaches are urgently needed for heterotypic protection ahead of time. Pivotal to this is the need to understand mechanisms that can deliver broad strain protection. Heterotypic and heterosubtypic humoral immunities have largely been overlooked for influenza cross-protection, with most 'seasoned' vaccine efforts for humans focussed on heterotypic cellular immunity. However, 5 years ago we began to identify direct and indirect indicators of humoral-herd immunity to protein sites preserved among H1N1, H3N2 and H5N1 influenzas. Since then the evidence for cross-protective antibodies in humans has been accumulating. Now proposed is a rationale to stimulate and enhance pre-existing heterotypic humoral responses that, together with cell-mediated initiatives, will deliver pre-emptive and universal human protection against emerging epidemic and pandemic influenzas.

Wide prevalence of heterosubtypic broadly neutralizing human anti-influenza A antibodies

BACKGROUND

Lack of life-long immunity against influenza viruses represents a major global health care problem with profound medical and economic consequences. A greater understanding of the broad-spectrum "heterosubtypic" neutralizing human antibody (BnAb) response to influenza should bring us closer toward a universal influenza vaccine.

METHODS

Serum samples obtained from 77 volunteers in an H5N1 vaccine study were analyzed for cross-reactive antibodies (Abs) against both subtype hemagglutinins (HAs) and a highly conserved pocket on the HA stem of Group 1 viruses. Cross-reactive Abs in commercial intravenous immunoglobulin were affinity purified using H5-coupled beads followed by step-wise monoclonal antibody competition or acid elution. Enzyme-linked immunosorbent assays were used to quantify cross-binding, and neutralization activity was determined with HA-pseudotyped viruses.

RESULTS

Prevaccination serum samples have detectable levels of heterosubtypic HA binding activity to both Group 1 and 2 influenza A viruses, including subtypes H5 and H7, respectively, to which study subjects had not been vaccinated. Two different populations of Broadly neutralizing Abs (BnAbs) were purified from intravenous immunoglobulin by H5 beads: ~0.01% of total immunoglobulin G can bind to HAs from both Group 1 and 2 and neutralize H1N1 and H5N1 viruses; ~0.001% is F10-like Abs directed against the HA stem pocket on Group 1 viruses.

CONCLUSION

These data--to our knowledge, for the first time--quantitatively show the presence, albeit at low levels, of two populations of heterosubtypic BnAbs against influenza A in human serum. These observations warrant further investigation to determine their origin, host polymorphism(s) that may affect their expression levels and how to boost these BnAb responses by vaccination to reach sustainable protective levels.

Coupling sensitive in vitro and in silico techniques to assess cross-reactive CD4(+) T cells against the swine-origin H1N1 influenza virus

The outbreak of the novel swine-origin H1N1 influenza in the spring of 2009 took epidemiologists, immunologists, and vaccinologists by surprise and galvanized a massive worldwide effort to produce millions of vaccine doses to protect against this single virus strain. Of particular concern was the apparent lack of pre-existing antibody capable of eliciting cross-protective immunity against this novel virus, which fueled fears this strain would trigger a particularly far-reaching and lethal pandemic. Given that disease caused by the swine-origin virus was far less severe than expected, we hypothesized cellular immunity to cross-conserved T cell epitopes might have played a significant role in protecting against the pandemic H1N1 in the absence of cross-reactive humoral immunity. In a published study, we used an immunoinformatics approach to predict a number of CD4(+) T cell epitopes are conserved between the 2008-2009 seasonal H1N1 vaccine strain and pandemic H1N1 (A/California/04/2009) hemagglutinin proteins. Here, we provide results from biological studies using PBMCs from human donors not exposed to the pandemic virus to demonstrate that pre-existing CD4(+) T cells can elicit cross-reactive effector responses against the pandemic H1N1 virus. As well, we show our computational tools were 80-90% accurate in predicting CD4(+) T cell epitopes and their HLA-DRB1-dependent response profiles in donors that were chosen at random for HLA haplotype. Combined, these results confirm the power of coupling immunoinformatics to define broadly reactive CD4(+) T cell epitopes with highly sensitive in vitro biological assays to verify these in silico predictions as a means to understand human cellular immunity, including cross-protective responses, and to define CD4(+) T cell epitopes for potential vaccination efforts against future influenza viruses and other pathogens.

Heterosubtypic antibody response elicited with seasonal influenza vaccine correlates partial protection against highly pathogenic H5N1 virus

Background

The spread of highly pathogenic avian influenza (HPAI) H5N1 virus in human remains a global health concern. Heterosubtypic antibody response between seasonal influenza vaccine and potential pandemic influenza virus has important implications for public health. Previous studies by Corti et al. and by Gioia et al. demonstrate that heterosubtypic neutralizing antibodies against the highly pathogenic H5N1 virus can be elicited with a seasonal influenza vaccine in humans. However, whether such response offers immune protection against highly pathogenic H5N1 virus remained to be determined.

Methodology/Principal Findings

In this study, using a sensitive influenza HA (hemagglutinin) and NA (neuraminidase) pseudotype-based neutralization (PN) assay we first confirmed that low levels of heterosubtypic neutralizing antibody response against H5N1 virus were indeed elicited with seasonal influenza vaccine in humans. We then immunized mice with the seasonal influenza vaccine and challenged them with lethal doses of highly pathogenic H5N1 virus. As controls, we immunized mice with homosubtypic H5N1 virus like particles (VLP) or PBS and challenged them with the same H5N1 virus. Here we show that low levels of heterosubtypic neutralizing antibody response were elicited with seasonal influenza vaccine in mice, which were significantly higher than those in PBS control. Among them 2 out of 27 whose immune sera exhibited similar levels of neutralizing antibody response as VLP controls actually survived from highly pathogenic H5N1 virus challenge.

Conclusions/Significance

Therefore, we conclude that low levels of heterosubtypic neutralizing antibody response are indeed elicited with seasonal influenza vaccine in humans and mice and at certain levels such response offers immune protection against severity of H5N1 virus infection.

A phase II, open-label, multicentre study to evaluate the immunogenicity and safety of an adjuvanted prepandemic (H5N1) influenza vaccine in healthy Japanese adults

Background

Promising clinical data and significant antigen-sparing have been demonstrated for a pandemic H5N1 influenza split-virion vaccine adjuvanted with AS03_A, an α-tocopherol-containing oil-in-water emulsion-based Adjuvant System. Although studies using this formulation have been reported, there have been no data for Japanese populations. This study therefore aimed to assess the immunogenicity and tolerability of a prepandemic (H5N1) influenza vaccine adjuvanted with AS03_A in Japanese adults.

Methods

This open-label, single-group study was conducted at two centres in Japan in healthy Japanese males and females aged 20-64 years (n = 100). Subjects received two doses of vaccine, containing 3.75 μg haemagglutinin of the A/Indonesia/5/2005-like IBCDC-RG2 Clade 2.1 (H5N1) strain adjuvanted with AS03_A, 21 days apart. The primary endpoint evaluated the humoral immune response in terms of H5N1 haemagglutination inhibition (HI) antibody titres against the vaccine strain (Clade 2.1) 21 days after the second dose. Ninety five percent confidence intervals for geometric mean titres, seroprotection, seroconversion and seropositivity rates were calculated. Secondary and exploratory endpoints included the assessment of the humoral response in terms of neutralising antibody titres, the response against additional H5N1 strains (Clade 1 and Clade 2.2), as well as the evaluation of safety and reactogenicity.

Results

Robust immune responses were elicited after two doses of the prepandemic influenza vaccine adjuvanted with AS03_A. Overall, vaccine HI seroconversion rates and seroprotection rates were 91% 21 days after the second vaccination. This fulfilled all regulatory acceptance criteria for the vaccine-homologous HI antibody level. A substantial cross-reactive humoral immune response was also observed against the virus strains A/turkey/Turkey/1/2005 (Clade 2.2) and A/Vietnam/1194/2004 (Clade 1) after the second vaccine administration. A marked post-vaccination response in terms of neutralising antibody titres was demonstrated and persistence of the immune response was observed 6 months after the first dose. The vaccine was generally well tolerated and there were no serious adverse events reported.

Conclusions

The H5N1 candidate vaccine adjuvanted with AS03_A elicited a strong and persistent immune response against the vaccine strain A/Indonesia/5/2005 in Japanese adults. Vaccination with this formulation demonstrated a clinically acceptable reactogenicity profile and did not raise any safety concerns in this population.

Trial registration

Clinicaltrials.gov NCT00742885

Inactivated split-virion seasonal influenza vaccine (Fluarix): a review of its use in the prevention of seasonal influenza in adults and the elderly

Fluarix is a trivalent, inactivated, split-virion influenza vaccine containing 15 microg haemagglutinin from each of the three influenza virus strains (including an H1N1 influenza A virus subtype, an H3N2 influenza A virus subtype and an influenza B virus) that are expected to be circulating in the up-coming influenza season. Fluarix is highly immunogenic in healthy adults and elderly, and exceeds the criteria that make it acceptable for licensure in various regions (including the US and Europe). In a large, phase III, placebo-controlled, double-blind trial conducted in the US (2004/2005) in subjects aged 18-64 years, postvaccination seroconversion rates against the H1N1, H3N2 and B antigens were 60-78% and respective postvaccination seroprotection rates were 97-99% in Fluarix recipients. Another phase III trial conducted in the US (2005/2006) established the noninferiority of Fluarix versus another trivalent inactivated influenza virus vaccine in subjects aged >or=18 years, including a subgroup of elderly subjects. In annual European registration trials, Fluarix has consistently exceeded the immunogenicity criteria set by the EU Committee for Medicinal Products for Human Use for adults and the elderly. Fluarix demonstrated immunogenicity in small, open-label studies in at-risk subjects. During a year when the vaccine was well matched to the circulating strain, Fluarix demonstrated efficacy against culture-confirmed influenza A and/or B in a placebo-controlled trial in adults aged 18-64 years. In addition, Fluarix vaccination of pregnant women demonstrated efficacy in reducing the rate of laboratory-confirmed influenza in the infants and reducing febrile respiratory illnesses in the mothers and their new-born infants in a randomized trial. Fluarix was generally well tolerated in adults and the elderly in well designed clinical trials and in the annual European registration trials, with most local and general adverse events being transient and mild to moderate in intensity. The most common adverse reactions in recipients of Fluarix were pain, redness or swelling at the injection site, muscle aches, fatigue, headache and arthralgia. In conclusion, Fluarix is an important means of decreasing the impact of seasonal influenza viruses on adults and the elderly.

Induction of cross-neutralizing antibody against H5N1 virus after vaccination with seasonal influenza vaccine in COPD patients

Archival serum samples from elderly individuals with underlying chronic obstructive pulmonary disease (COPD) who were enrolled in a double-blind case-control study of seasonal influenza vaccine efficacy were assayed for cross-neutralizing antibody formation to avian influenza A (H5N1) virus. Of 118 serum samples, 58 were collected from influenza vaccinees (mean age 68.5 y), and 60 from placebo controls (mean age 68.4 y) who received vitamin B injections. Blood samples were collected before and at 1 mo after seasonal influenza vaccination from all subjects; in addition, for a longitudinal follow-up period of 1 y paired-blood samples were collected again from subjects who developed acute respiratory illness. Hemagglutination inhibition assay for antibodies to influenza A (H1N1), influenza A (H3N2), and influenza B viruses was carried out to determine the serological response to vaccination, and to diagnose influenza viral infection, while microneutralization assays were performed to detect cross-reactive antibody to H5N1 virus. Pre-existing cross-reactive H5N1 antibody at reciprocal titer 10 was found in 6 (10.3%) vaccinees and 4 (6.7%) placebo controls. There was no change in H5N1 antibody titer in these subjects after vaccination. On the other hand, 3 (5.2%) vaccinees developed seroconversion to H5N1 virus at 1 mo after vaccination, even though they had no pre-existing H5N1 antibody in their first blood samples. No cross-neutralizing antibody to H5N1 virus was detected in the placebo controls or in the 22 influenza patients, suggesting that influenza vaccination, but not influenza virus infection, induces cross-neutralizing antibody against avian influenza H5N1 virus.

Immunogenicity and Safety of H5N1 A/Vietnam/1194/2004 (Clade 1) AS03-adjuvanted prepandemic candidate influenza vaccines in children aged 3 to 9 years: a phase ii, randomized, open, controlled study

BACKGROUND

The development of vaccines against pandemic influenza viruses for use in children is a public health priority.

METHODS

In this phase II, randomized, open study, the immunogenicity and reactogenicity of H5N1 A/Vietnam/1194/2004 (NIBRG-14) (clade 1) prepandemic influenza vaccine were assessed in children aged 3 to 5 and 6 to 9 years. Children were randomized to receive 2 doses, given 21 days apart, of A/Vietnam/1194/2004 vaccine containing 1.9 microg or 3.75 microg hemagglutinin antigen (HA), adjuvanted with a tocopherol-based oil-in-water emulsion (AS03) containing 11.86 mg (AS03(A)) or 5.93 mg (AS03(B)) tocopherol. Control groups received 2 doses of trivalent influenza vaccine (TIV). Humoral immune responses, reactogenicity, and safety were the primary outcome measures; cross-reactivity and cell-mediated responses were also assessed (NCT00502593).

RESULTS

Between 49 and 51 children in each age stratum (aged 3-5 and 6-9 years) received H5N1 vaccine, and between 17 and 18 children in each age stratum received TIV. After the second dose, recipients of H5N1 vaccine (1.9 microg HA/AS03(B), 3.75 microg HA/AS03(B), and 3.75 microg HA/AS03(A)) achieved humoral antibody titers against the vaccine-homologous strain, which fulfilled the United States influenza vaccines licensure criteria for immunogenicity. With the exception of 1 child, there were no H5N1 immune responses in children who received TIV. The most frequent injection-site event was pain in all groups, and the H5N1 vaccine had a clinically acceptable reactogenicity and safety profile. Exploratory analyses in children aged 3 to 5 years indicated that the induction of CD4 T-cell responses polarized in favor of a T-helper 1 profile.

CONCLUSIONS

The results showed that 2 doses of AS03-adjuvanted H5N1 influenza vaccine at antigen-sparing doses of 1.9 microg or 3.75 microg HA elicited broad and persistent immune responses with acceptable reactogenicity, and without safety concerns, in children aged 3 to 9 years.