Prepandemic Influenza Vaccine Research Articles

The antibody landscapes following AS03 and MF59 adjuvanted H5N1 vaccination

Current seasonal and pre-pandemic influenza vaccines induce short-lived predominantly strain-specific and limited heterosubtypic responses. To better understand how vaccine adjuvants AS03 and MF59 may provide improved antibody responses to vaccination, we interrogated serum from subjects who received 2 doses of inactivated monovalent influenza A/Indonesia/05/2005 vaccine with or without AS03 or MF59 using hemagglutinin (HA) microarrays (NCT01317758 and NCT01317745). The arrays were designed to reflect both full-length and globular head HA derived from 17 influenza A subtypes (H1 to H16 and H18) and influenza B strains. We observed significantly increased strain-specific and broad homo- and heterosubtypic antibody responses with both AS03 and MF59 adjuvanted vaccination with AS03 achieving a higher titer and breadth of IgG responses relative to MF59. The adjuvanted vaccine was also associated with the elicitation of stalk-directed antibody. We established good correlation of the array antibody responses to H5 antigens with standard HA inhibition and microneutralization titers.

Development and characterization of standard reagents for cell-based prepandemic influenza vaccine products

ABSTRACT Outbreaks of infection by novel avian influenza virus strains in humans cause public health issues worldwide, and the development of vaccines against such novel strains is the most effective method for the prevention of these virus outbreaks. All types of vaccines must be tested for potency before use; thus, quantitative potency assays are needed for influenza vaccines. The single radial immunodiffusion (SRID) assay is considered the gold standard for quantification of influenza virus antigens, and the SRID reference reagents are essential for the determination of vaccine potency. However, it remains debatable whether reference reagents derived from egg-based vaccine platforms can be used to precisely quantify non-egg-derived vaccines; thus, influenza vaccine production using cell-based platforms has attracted increasing attention. To evaluate the utility of reference reagents derived from a cell-based influenza vaccine platform, we prepared cell-based reference reagents from MDCK cell-grown viruses and compared them with egg-derived reference reagents. A primary liquid standard (PLS) was purified from cell-derived candidate influenza vaccine viruses, and hemagglutinin (HA) antigen content was determined by a densitometric method. The produced PLS could be stored at 4°C for more than 10 months. We also established a simple HA protein purification method for goat antiserum preparation, and the performance of the resulting antiserum was compared to that of standard reagents obtained using different production platforms. The results of this study indicate that these reference reagents can be used for both cell-based and egg-based production platforms and that the differences between these two types of platforms are negligible.

Effectiveness, immunogenicity, and safety of influenza vaccines with MF59 adjuvant in healthy people of different age groups: A systematic review and meta-analysis.

Influenza is a severe disease burden among all age groups. This study aimed to review the efficacy of inactivated influenza vaccines with MF59 adjuvant and non-adjuvanted inactivated influenza vaccines among all age groups against specific influenza vaccine strains. Literature search of PubMed, Embase, Medline, OVID, and Cochrane Library Trials (CENTRAL) was implemented up to March 1, 2019. Homogeneity qualified studies were included forData were extracted such as study country location, demographic characteristics, and measure outcomes, and were analyzed by a random effect model and sensitivity analyses to identify heterogeneity. Risk of bias was evaluated using the Cochrane Risk of Bias Tool. We retrieved 1,021 publications and selected 31 studies for full review, including 17 trials for meta-analysis and 6 trials for qualitative synthesis. MF59-adjuvanted influenza vaccines demonstrated better immunogenicity against specific vaccine virus strains compared to non-adjuvanted influenza vaccine both in healthy adult group (RR = 2.10; 95% CI: 1.28-3.44) and the healthy aged (RR = 1.26; 95% CI: 1.10-1.44). The quality of evidence is moderate to high for seroconversion and seroprotection rates of influenza vaccine. MF59-adjuvanted influenza vaccines are superior to non-adjuvanted influenza vaccines to enhance immune responses of vaccination in healthy adults and older adults, and could be considered for routine use especially the monovalent prepandemic influenza vaccines.

A Phase 2/3 double blinded, randomized, placebo-controlled study in healthy adult participants in Vietnam to examine the safety and immunogenicity of an inactivated whole virion, alum adjuvanted, A(H5N1) influenza vaccine (IVACFLU-A/H5N1)

BackgroundA global shortfall of vaccines for avian influenza A(H5N1) would occur, especially in low- and-middle income countries, if a pandemic were to occur. To address this issue, development of a pre-pandemic influenza vaccine was initiated in 2012, leveraging a recently established influenza vaccine manufacturing capacity in Vietnam. MethodsThis was a Phase 2/3, double-blinded, randomized, placebo-controlled study to test the safety and immunogenicity of IVACFLU-A/H5N1 vaccine in healthy adults. Phase 2 was a dose selection study, in which 300 participants were randomized to one of the three groups (15 mcg, 30 mcg, or placebo). Safety and immunogenicity were assessed in all participants. In Phase 3, 630 participants were randomized to receive the IVACFLU-A/H5N1 vaccine dose selected in Phase 2 (15 mcg, n = 525) or placebo (n = 105). Safety was assessed in all Phase 3 participants and immunogenicity was measured in a subset of participants. ResultsThe vaccine was well tolerated and most of the adverse events were mild and of short duration. Mild pain at the injection site was the most common adverse event seen in 60 percent of participants in the vaccine group in Phase 3. In Phase 2, both 15 mcg and 30 mcg doses were immunogenic, so the lower dose was selected for further testing in Phase 3. In Phase 3 overall seroconversion rates were 68 percent for hemagglutination inhibition (HI), 51 percent for microneutralization (MN) and 56 percent for single radial hemolysis (SRH). The seroprotection rates were 44 percent for HI, 41 percent for MN and 55 percent for SRH. The GMT ratio was 5.31 and 3.7 for HI and MN respectively; GMA was 4.75 for the SRH. ConclusionThe IVACFLU A/H5N1 was safe and immunogenic. Development of this pandemic avian influenza vaccine is a welcome addition to the limited global pool of these vaccines.ClinicalTrials.gov register NCT02612909.

Human medicines European public assessment report (EPAR): Vepacel, Prepandemic influenza vaccine (H5N1) (whole virion, inactivated,prepared in cell culture), Influenza, Human,Immunization,Disease Outbreaks, Date of authorisation: 17/02/2012, Revision: 9, Status: Authorised

Human medicines European public assessment report (EPAR): Vepacel, Prepandemic influenza vaccine (H5N1) (whole virion, inactivated,prepared in cell culture), Influenza, Human,Immunization,Disease Outbreaks, Date of authorisation: 17/02/2012, Revision: 9, Status: Authorised

Human medicines European public assessment report (EPAR): Vepacel, Prepandemic influenza vaccine (H5N1) (whole virion, inactivated,prepared in cell culture), Influenza, Human,Immunization,Disease Outbreaks, Date of authorisation: 17/02/2012, Revision: 9, Status: Authorised

Human medicines European public assessment report (EPAR): Vepacel, Prepandemic influenza vaccine (H5N1) (whole virion, inactivated,prepared in cell culture), Influenza, Human,Immunization,Disease Outbreaks, Date of authorisation: 17/02/2012, Revision: 9, Status: Authorised

Safety and immunogenicity of influenza A(H5N1) vaccine stored up to twelve years in the National Pre-Pandemic Influenza Vaccine Stockpile (NPIVS)

BackgroundAs part of the U.S. Department of Health and Human Services (HHS) Pandemic Influenza Plan preparedness and response strategy, the National Pre-Pandemic Influenza Vaccine Stockpile (NPIVS) program was established by the Biomedical Advanced Research and Development Authority (BARDA) in 2005 with the goal of building and maintaining a stockpile of vaccines for influenza viruses with pandemic potential to vaccinate 20 million people in the critical workforce in the event of a pandemic. The NPIVS program continuously monitors the integrity of influenza vaccine antigens and adjuvants stored within the stockpile. In addition to monitoring physical and chemical properties in stability studies, it is important to regularly assess the safety and immunogenicity of stockpiled vaccines and adjuvants to maintain preparedness for use in the event of an influenza pandemic. MethodsBARDA conducted a randomized, double-blinded Phase 2 clinical study with the oldest stockpiled influenza A(H5N1) antigen, stored over the previous 10–12 years administered with or without MF59® adjuvant, stored over the previous 2–7 years at the time of vaccination. ResultsStockpiled vaccines were well-tolerated, adverse events were generally mild, and there was no drop in immunogenicity to the oldest stockpiled A(H5N1) vaccine. Compared to unadjuvanted vaccine, greater peak antibody responses were observed in subjects who were vaccinated with MF59-adjuvanted vaccines, regardless of antigen dose. Vaccination with the A(H5N1) vaccine antigen also results in cross-reactive antibody responses to contemporary circulating strains of A(H5) influenza viruses. ConclusionsThe frequency, type, and severity of AEs observed during this study are similar to historical clinical study data with A(H5N1) vaccines and MF59 adjuvant indicating that a stockpiled A(H5N1) vaccine appears to remain safe and tolerable. The vaccines were immunogenic when administered as a two-dose vaccine regimen in healthy adults, despite extended storage of HA antigen or MF59 adjuvant within the NPIVS. Trial registration:ClinicalTrials.gov: NCT02680002.

Aluminum salts as an adjuvant for pre-pandemic influenza vaccines: a meta-analysis

Avian-origin H5/H7 influenza has the potential to cause the next influenza pandemic. Availability of effective vaccines is an essential part of pre-pandemic preparedness. However, avian influenza surface antigens are poorly immunogenic to humans, which necessitates the use of adjuvants to augment the immunogenicity of pre-pandemic influenza vaccines. Aluminum salts are approved, safe, and affordable adjuvants, but their adjuvanticity for influenza vaccines remains unverified. We conducted the first meta-analysis on this issue. A total of nine randomized controlled trials (2006–2013, 22 comparisons, 2,467 participants in total) compared aluminum-adjuvanted H5N1 vaccines versus non-adjuvanted counterparts. The weighted estimate for the ratio of the seroprotection rate after a single dose of H5N1 vaccine is 0.66 (95% CI: 0.53 to 0.83) by hemagglutination-inhibition assay or 0.56 (95% CI: 0.42 to 0.74) by neutralizing titer assay. The weighted estimate for the risk ratio of pain/tenderness at injection sites is 1.85 (95% CI: 1.56 to 2.19). The quality of evidence is low to very low for seroprotection (due to indirectness and potential reporting bias) and moderate for pain/tenderness (due to potential reporting bias), respectively. The significantly lower seroprotection rate after aluminum-adjuvanted H5N1 vaccines and the significantly higher risk of pain at injection sites indicate that aluminum salts decrease immunogenicity but increase local reactogenicity of pre-pandemic H5N1 vaccines in humans.

Stockpiled pre-pandemic H5N1 influenza virus vaccines with AS03 adjuvant provide cross-protection from H5N2 clade 2.3.4.4 virus challenge in ferrets

Avian influenza viruses, notably H5 subtype viruses, pose a continuous threat to public health due to their pandemic potential. In recent years, influenza virus H5 subtype split vaccines with novel oil-in-water emulsion based adjuvants (e.g. AS03, MF59) have been shown to be safe, immunogenic, and able to induce broad immune responses in clinical trials, providing strong scientific support for vaccine stockpiling. However, whether such vaccines can provide protection from infection with emerging, antigenically distinct clades of H5 viruses has not been adequately addressed. Here, we selected two AS03-adjuvanted H5N1 vaccines from the US national pre-pandemic influenza vaccine stockpile and assessed whether the 2004-05 vaccines could provide protection against a 2014 highly pathogenic avian influenza (HPAI) H5N2 virus (A/northern pintail/Washington/40964/2014), a clade 2.3.4.4 virus responsible for mass culling of poultry in North America. Ferrets received two doses of adjuvanted vaccine containing 7.5µg of hemagglutinin (HA) from A/Vietnam/1203/2004 (clade 1) or A/Anhui/1/2005 (clade 2.3.4) virus either in a homologous or heterologous prime-boost vaccination regime. We found that both vaccination regimens elicited robust antibody responses against the 2004-05 vaccine viruses and could reduce virus-induced morbidity and viral replication in the lower respiratory tract upon heterologous challenge despite the low level of cross-reactive antibody titers to the challenge H5N2 virus. This study supports the value of existing stockpiled 2004-05 influenza H5N1 vaccines, combined with AS03-adjuvant for early use in the event of an emerging pandemic with H5N2-like clade 2.3.4.4 viruses.

Cell-cultured, live attenuated, X-31ca-based H5N1 pre-pandemic influenza vaccine

The manufacture of influenza vaccines has traditionally depended upon a method using embryonated hen's eggs. However, concerns regarding the potential shortage of the influenza substrate in the event of a pandemic has led to the development of cell culture-derived vaccines, which offers shorter lead-in times and greater production flexibility. We examined optimal conditions for the production of reassortant X-31ca-based H5N1 cold-adapted live attenuated influenza vaccine (rH5N1ca) cultured in mammalian cell lines. During ten passages in MDCK cells, the rH5N1ca vaccine maintained cold-adapted and temperature-sensitive phenotypes, and no mutations occurred in the hemagglutinin and neuraminidase surface antigens, demonstrating genetic and phenotypic stability. Single immunization in mice with the rH5N1ca induced robust antibody responses and protected the mice against lethal challenge. Stable maintenance of attenuation phenotypes and immunogenicity of the rH5N1ca from cell-culture suggest that they can be produced as a stockpile for pandemic preparedness as an alternative to current egg-based production.

Randomized, double-blind, multi-center, phase III clinical trial to evaluate the immunogenicity and safety of MG1109 (egg-based pre-pandemic influenza A/H5N1 vaccine) in healthy adults

ABSTRACTConsidering the pandemic potential of avian influenza A/H5N1, development of an effective and well-tolerated vaccine is an essential part of pandemic preparedness plans. This phase III, randomized, double-blind study was conducted to assess the immunogenicity and safety profile of an alum-adjuvanted, whole virion, pre-pandemic influenza A/H5N1 vaccine (MG1109). Healthy individuals were randomly assigned, in a 3:1 ratio, to receive two doses of either MG1109 or placebo containing alum gel. Immunogenicity was determined by hemagglutination inhibition (HI) and microneutralization (MN) assays. Solicited and unsolicited adverse events were assessed after vaccination. Among 420 enrolled subjects, 418 were available for safety analysis, and 298 MG1109 recipients were available for per-protocol immunogenicity analyses. According to the HI assays, after two vaccine doses, all three of the Committee for Medicinal Products for Human Use (CHMP) criteria were met against the vaccine strain for all age groups: seroprotection rate = 74.8% (95% CI: 69.9 – 79.8), seroconversion rate = 67.8% (95% CI: 62.5–73.1), and geometric mean titer ratio (GMTR) = 5.9 (95% CI: 5.4 – 6.4). According to the MN assays, the GMTR was 2.4 (95% CI: 2.1 – 2.7) and 7.0 (95% CI: 6.3 – 7.9) three weeks after the first and second vaccine doses, respectively. Solicited local and systemic adverse events were mostly mild to moderate and were not significantly different between MG1109 and placebo recipients. In conclusion, two-dose administration of alum-adjuvanted H5N1 pre-pandemic influenza vaccine (MG1109) was highly immunogenic and tolerable in adults.

Antibody-Dependent Cell-Mediated Cytotoxicity to Hemagglutinin of Influenza A Viruses After Influenza Vaccination in Humans.

Background. Detection of neutralizing antibodies (nAbs) to influenza A virus hemagglutinin (HA) antigens by conventional serological assays is currently the main immune correlate of protection for influenza vaccines However, current prepandemic avian influenza vaccines are poorly immunogenic in inducing nAbs despite considerable protection conferred. Recent studies show that Ab-dependent cell-mediated cytotoxicity (ADCC) to HA antigens are readily detectable in the sera of healthy individuals and patients with influenza infection. Methods. Virus neutralization and ADCC activities of serum samples from individuals who received either seasonal or a stock-piled H5N1 avian influenza vaccine were evaluated by hemagglutination inhibition assay, microneutralization assay, and an improved ADCC natural killer (NK) cell activation assay. Results. Immunization with inactivated seasonal influenza vaccine led to strong expansion of both nAbs and ADCC-mediating antibodies (adccAbs) to H3 antigen of the vaccine virus in 24 postvaccination human sera. In sharp contrast, 18 individuals vaccinated with the adjuvanted H5N1 avian influenza vaccine mounted H5-specific antibodies with strong ADCC activities despite moderate virus neutralization capacity. Strength of HA-specific ADCC activities is largely associated with the titers of HA-binding antibodies and not with the fine antigenic specificity of anti-HA nAbs. Conclusions. Detection of both nAbs and adccAbs may better reflect protective capacity of HA-specific antibodies induced by avian influenza vaccines.

A clinical phase I study of an EB66 cell-derived H5N1 pandemic vaccine adjuvanted with AS03

BackgroundWe conducted a phase I clinical trial of a cell culture-derived AS03-adjuvanted influenza vaccine containing HA antigen (A/Indonesia/05/2005(H5N1)/PR8-IBCDC-RG2) derived from EB66 cells (KD-295). MethodsHealthy male adult volunteers (20–40 years old, N=60) enrolled in the study were divided into 3 groups, the MA group (3.8μg of HA+AS03), HA group (7.5μg of HA+AS03), and 1/2 MA group (half the volume of the MA group), and received KD-295 intramuscularly twice with a 21-day interval. After administration of KD-295, adverse events, clinical laboratory parameters, and immune response to the vaccine strain and heterologous virus strains were evaluated. ResultsNo severe adverse events leading to discontinuation of vaccine administration occurred. The vaccine was well-tolerated. There was no dose dependency in the rate, timing, or duration of the adverse events. Immunogenicity of the vaccines was evaluated by HI (hemagglutination inhibition) assay, which confirmed that the antibody response to the vaccine strain and heterologous strain in all groups met the three criteria for immunogenicity described in the Japanese guidelines for development of a pandemic prototype vaccine. We also measured the neutralizing antibody titers against several virus strains, and confirmed a significant rise in antibody levels to both the vaccine strain and heterologous strains. ConclusionThe EB66-derived H5N1 influenza vaccine adjuvanted with AS03 elicited a broad cross-reactive antibody response among H5N1 strains with acceptable reactogenicity. Therefore, KD-295 can be considered a useful pandemic and pre-pandemic influenza vaccine candidate.

Market implementation of the MVA platform for pre-pandemic and pandemic influenza vaccines: A quantitative key opinion leader analysis

A quantitative method is presented to rank strengths, weaknesses, opportunities, and threats (SWOT) of modified vaccinia virus Ankara (MVA) as a platform for pre-pandemic and pandemic influenza vaccines. Analytic hierarchy process (AHP) was applied to achieve pairwise comparisons among SWOT factors in order to prioritize them. Key opinion leaders (KOLs) in the influenza vaccine field were interviewed to collect a unique dataset to evaluate the market potential of this platform.The purpose of this study, to evaluate commercial potential of the MVA platform for the development of novel generation pandemic influenza vaccines, is accomplished by using a SWOT and AHP combined analytic method. Application of the SWOT–AHP model indicates that its strengths are considered more important by KOLs than its weaknesses, opportunities, and threats. Particularly, the inherent immunogenicity capability of MVA without the requirement of an adjuvant is the most important factor to increase commercial attractiveness of this platform. Concerns regarding vector vaccines and anti-vector immunity are considered its most important weakness, which might lower public health value of this platform. Furthermore, evaluation of the results of this study emphasizes equally important role that threats and opportunities of this platform play.This study further highlights unmet needs in the influenza vaccine market, which could be addressed by the implementation of the MVA platform. Broad use of MVA in clinical trials shows great promise for this vector as vaccine platform for pre-pandemic and pandemic influenza and threats by other respiratory viruses. Moreover, from the results of the clinical trials seem that MVA is particularly attractive for development of vaccines against pathogens for which no, or only insufficiently effective vaccines, are available.

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.

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

Heat shock protein gp96 adjuvant induces T cell responses and cross-protection to a split influenza vaccine

The commonly used inactivated or split influenza vaccines induce only induce minimal T cell responses and are less effective in preventing heterologous virus infection. Thus, developing cross-protective influenza vaccines against the spread of a new influenza virus is an important strategy against pandemic emergence. Here we demonstrated that immunization with heat shock protein gp96 as adjuvant led to a dramatic increased antigen-specific T cell response to a pandemic H1N1 split vaccine. Notably, gp96 elicited a cross-protective CD8+ T cell response to the internal conserved viral protein NP. Although the split pH1N1vaccine alone has low cross-protective efficiency, adding gp96 as an adjuvant effectively improved the cross-protection against challenge with a heterologous virus in mice. Our study reveals the novel property of gp96 in boosting the T cell response against conserved epitopes of influenza virus and its potential use as an adjuvant for human pre-pandemic inactivated influenza vaccines against different viral subtypes.

Influenza vaccines: an Asia–Pacific perspective

This article provides an overview of some aspects of seasonal, pre-pandemic and pandemic influenza vaccines and initiatives aimed to increase influenza vaccine use within the Asia-Pacific region. Expanding the use of influenza vaccines in the Asia-Pacific region faces many challenges. Despite the recent regional history for the emergence of novel viruses, SARS, the H5N1 and H7N9, and the generation of and global seeding of seasonal influenza viruses and initiatives by WHO and other organisations to expand influenza awareness, the use of seasonal influenza vaccines remains low. The improvement in current vaccine technologies with the licensing of quadrivalent, live-attenuated, cell culture-based, adjuvanted and the first recombinant influenza vaccine is an important step. The development of novel influenza vaccines able to provide improved protection and with improved manufacturing capacity is also advancing rapidly. However, of ongoing concern are seasonal influenza impact and the low use of seasonal influenza vaccines in the Asia-Pacific region. Improved influenza control strategies and their implementation in the region are needed. Initiatives by the World Health Organization (WHO), and specifically the Western Pacific Regional Office of WHO, are focusing on consistent vaccine policies and guidelines in countries in the region. The Asian-Pacific Alliance for the Control of Influenza (APACI) is contributing through the coordination of influenza advocacy initiates.

An Inactivated, Adjuvanted Whole Virion Clade 2.2 H5N1 (A/Chicken/Astana/6/05) Influenza Vaccine Is Safe and Immunogenic in a Single Dose in Humans

In this study, we assessed in humans the immunogenicity and safety of one dose (7.5 or 15 μg of hemagglutinin [HA]) of a whole-virion inactivated prepandemic influenza vaccine adjuvanted with aluminum hydroxide. The vaccine strain was made by reverse genetics from the highly pathogenic avian A/Chicken/Astana/6/05 (H5N1) clade 2.2 strain isolated from a dead bird in Kazakhstan. The humoral immune response was evaluated after a single vaccination by hemagglutination inhibition (HI) and microneutralization (MN) assays. The vaccine was safe and immunogenic, inducing seroconversion in 55% of the evaluated patients, with a geometric mean titer (GMT) of 17.1 and a geometric mean increase (GMI) of 3.42 after a dose of 7.5 μg in the HI test against the vaccine strain. The rate of seroconversion increased up to 70% when the dose of 15 μg was used. The percentages of individuals achieving anti-HA titers of ≥1:40 were 52.5% and 57.5% for the 7.5- and 15-μg dose groups, respectively. Similar results were obtained when antibodies were analyzed in an MN test. Substantial cross-neutralization titers (seroconversion in 35% and 52.5% of subjects in the two dose groups, respectively) were detected against heterologous clade 1 strain NIBRG14 (H5N1). Thus, one dose of this whole-virion prepandemic vaccine adjuvanted with aluminum has the potential to be effective against H5N1 viruses of different clades.

Immunogenicity and protective efficacy of cold-adapted X-31 live attenuated pre-pandemic H5N1 influenza vaccines

Despite global efforts to control influenza viruses, they have taken a heavy toll on human public health worldwide. Among particular threats is highly pathogenic avian H5N1 influenza virus (HPAI) due to not only its high mortality in humans but also possible human-to-human transmission either through reassortment with other human influenza viruses such as 2009 pandemic H1N1 influenza virus, or by genetic mutations. With the aim of developing effective vaccines against the H5N1 viruses, we generated two live attenuated H5N1 vaccine candidates against A/Indonesia/05/2005 (clade 2.1) and A/chicken/Korea/ES/2003 (clade 2.5) strains, in the genetic background of the cold-adapted donor strain of X-31. In mice, a single dose of immunization with each of the two vaccines was highly immunogenic inducing high titers of serum viral-neutralizing and hemagglutinin-inhibiting antibodies against the homologous H5N1 strain. Furthermore, significant levels of cross-clade antibody responses were induced by the vaccines, suggesting a broad-spectrum cross-reactivity against the heterologous H5N1 strains. The immunizations provided solid protections against heterologous lethal challenges with H5N2 virus, significantly reducing the morbidity and challenge virus replications in the respiratory tracts. The robustness of the antibody responses against both the homologous and heterologous strains, together with efficient protection against the lethal H5N2 challenge, strongly support the protection against wild type H5N1 infections. These results could serve as an experimental basis for the development of safe and effective H5N1 pre-pandemic vaccines while further addressing the biosecurity concerns associated with H5N1 HPAI.

Combined Administration of MF59-Adjuvanted A/H5N1 Prepandemic and Seasonal Influenza Vaccines: Long-Term Antibody Persistence and Robust Booster Responses 1 Year after a One-Dose Priming Schedule

Having previously demonstrated the feasibility of administering A/H5N1 and seasonal influenza vaccine antigens in an MF59-adjuvanted tetravalent formulation, we now report on long-term antibody persistence and responses to a booster dose of a combined seasonal-pandemic, tetravalent influenza vaccine in adults. The primary objective was the evaluation of responses to a booster dose of tetravalent influenza vaccine containing seasonal (A/H1N1, A/H3N2, and B) and avian (A/H5N1, clade 2) influenza virus strains administered to 265 healthy 18- to 40-year-old volunteers 1 year after priming with one or two clade 1 A/H5N1 doses. Secondary objectives were assessment of reactogenicity, safety, and antibody persistence 1 year after priming with a combined seasonal-pandemic, tetravalent vaccine. Responses to seasonal strains met all European licensure criteria; seroprotection rates were 94 to 100%, 100%, and 61 to 90% for A/H1N1, A/H3N2, and B strains, respectively. Anamnestic responses were observed against homologous and heterologous A/H5N1 strains whether priming with one or two A/H5N1 doses, with a monovalent A/H5N1 vaccine, or with a tetravalent vaccine. A single dose of MF59-adjuvanted A/H5N1 vaccine given alone or as part of a fixed combination with a seasonal influenza vaccine was sufficient to prime adult subjects, resulting in robust antigen-specific and cross-reactive antibody responses to heterologous booster immunization 1 year later. These data support the feasibility of incorporating prepandemic priming into seasonal influenza vaccination programs. (This study has been registered at clinicaltrials.gov under registration no. NCT00481065.).