Potency of an inactivated influenza vaccine prepared from A/duck/Mongolia/119/2008 (H7N9) against the challenge with A/Anhui/1/2013 (H7N9)

H7N9 influenza virus infection in humans was reported in China on March 31, 2013. Humans are immunologically naïve to the H7N9 subtype, for which the seasonal influenza vaccine is not effective. Thus, the development of an H7N9 influenza virus vaccine is an urgent issue. To prepare for the emergence of an influenza pandemic, we have established a library comprising more than 1300 influenza virus strains with 144 different combinations of 16 HA and 9 NA subtypes. An H7N9 virus strain isolated from a 35-year-old woman, A/Anhui/1/2013 (H7N9), was found to be antigenically similar to H7N9 influenza viruses isolated from migratory ducks. In the present study, the potency of an inactivated whole virus particle vaccine prepared from an H7N9 low pathogenic avian influenza virus, A/duck/Mongolia/119/2008 (H7N9), selected from the library, was assessed by a challenge with A/Anhui/1/2013 (H7N9). The results indicate that the test vaccine was potent enough to induce sufficient immunity to reduce the impact of disease caused by the challenge with A/Anhui/1/2013 (H7N9) in mice. The present results indicate that an inactivated whole virus particle vaccine prepared from an influenza virus strain stored in the library could be useful as a vaccine strain in case of an influenza pandemic.     

A highly immunogenic vaccine against A/H7N9 influenza virus

Since the first case of human infection in March 2013, continued reports of H7N9 cases highlight a potential pandemic threat. Highly immunogenic vaccines to this virus are urgently needed to protect vulnerable populations who lack protective immunity. In this study, an egg- and adjuvant-independent adenoviral vector-based, hemagglutinin H7 subtype influenza vaccine (HAd-H7HA) demonstrated enhanced cell-mediated immunity as well as serum antibody responses in a mouse model. Most importantly, this vaccine provided complete protection against homologous A/H7N9 viral challenge suggesting its potential utility as a pandemic vaccine.     

Development of a high-yield reassortant influenza vaccine virus derived from the A/Anhui/1/2013 (H7N9) strain

In April 2013, the first three fatal cases of human infection with an avian influenza A virus (H7N9) were reported in China. Because of a pandemic threat by this virus, we have commenced to develop candidate vaccine viruses (CVVs). Three 6:2 genetic reassortant viruses with different hemagglutinin (HA) sequences, NIIDRG-10, -10.1 and -10.2, were generated by a reverse genetics technique between the high egg-growth master virus, A/Puerto Rico/8/34 (H1N1) and A/Anhui/1/2013 (H7N9), kindly provided by the Chinese Center for Disease Control and Prevention. The different HA gene sequences of the three CVVs were derived from the original virus stock. NIIDRG-10 possesses HA, whose sequence is identical to that of the original A/Anhui/1/2013 (H7N9) in the Global Initiative on Sharing Avian Influenza Data (EPI439507), while NIIDRG-10.1 and -10.2 possess amino acid differences, A125T and N123D/N149D, respectively, compared with NIIDRG-10. NIIDRG-10 replicated in embryonated chicken eggs with low hemagglutination titer 128, whereas NIIDRG-10.1 and -10.2 grew well with hemagglutination titer 1024. These viruses reacted well with a ferret antiserum raised against the original A/Anhui/1/2013 virus. Ferret antiserum against NIIDRG-10.1 reacted well with A/Anhui/1/2013 similar to the homologous virus NIIDRG-10.1. These results indicated that NIIDRG-10.1 passed the two-way test of antigenic identity. In contrast, the ferret antiserum against NIIDRG-10.2 reacted with A/Anhui/1/2013 at an 8-fold lower hemagglutination inhibition titer than with the homologous virus NIIDRG-10.2, indicating an antigenic change. The total and HA protein yields of NIIDRG-10.1 were 14.7 and 6.9 μg/ml, respectively, similar to those levels of high-yield seed viruses of seasonal influenza vaccines. NIIDRG-10.1 was approved as one of the CVVs for H7N9 viruses by the WHO in 2013. The candidate vaccine derived from NIIDRG-10.1 is currently being evaluated in a phase II clinical study in Japan.     

Plant-derived H7 VLP vaccine elicits protective immune response against H7N9 influenza virus in mice and ferrets

In March 2013, the Chinese Centre for Disease Control and Prevention confirmed the first reported case of human infection with an avian influenza A H7N9 virus. Infection with this virus often caused severe pneumonia and acute respiratory distress syndrome resulting in a case fatality rate >35%. The risk of pandemic highlighted, once again, the need for a more rapid and scalable vaccine response capability. Here, we describe the rapid (19 days) development of a plant-derived VLP vaccine based on the hemagglutinin sequence of influenza H7N9 A/Hangzhou/1/2013. The immunogenicity of the H7 VLP vaccine was assessed in mice and ferrets after one or two intramuscular dose(s) with and without adjuvant (alum or GLA-SE™). In ferrets, we also measured H7-specific cell-mediated immunity. The mice and ferrets were then challenged with H7N9 A/Anhui/1/2013 influenza virus. A single immunization with the adjuvanted vaccine elicited a strong humoral response and protected mice against an otherwise lethal challenge. Two doses of unadjuvanted vaccine significantly increased humoral response and resulted in 100% protection with significant reduction of clinical signs leading to nearly asymptomatic infections. In ferrets, a single immunization with the alum-adjuvanted H7 VLP vaccine induced strong humoral and CMI responses with antigen-specific activation of CD3⁺ T cells. Compared to animals injected with placebo, ferrets vaccinated with alum-adjuvanted vaccine displayed no weight loss during the challenge. Moreover, the vaccination significantly reduced the viral load in lungs and nasal washes 3 days after the infection. This candidate plant-made H7 vaccine therefore induced protective responses after either one adjuvanted or two unadjuvanted doses. Studies are currently ongoing to better characterize the immune response elicited by the plant-derived VLP vaccines. Regardless, these data are very promising for the rapid production of an immunogenic and protective vaccine against this potentially pandemic virus.     

Advancing new vaccines against pandemic influenza in low-resource countries

With the support of the Biomedical Advanced Research and Development Authority (BARDA), PATH is working with governments and vaccine manufacturers to strengthen their influenza vaccine manufacturing capacity and improve their ability to respond to emerging pandemic influenza viruses. Vaccines directed against influenza A/H5N1 and A/H7N9 strains are a particular focus, given the potential for these viruses to acquire properties that may lead to a pandemic. This paper will review influenza vaccine development from a developing country perspective and PATH's support of this effort. Several vaccines are currently in preclinical and clinical development at our partners for seasonal and pandemic influenza in Vietnam (IVAC and VABIOTECH), Serbia (Torlak), China (BCHT), Brazil (Butantan), and India (SII). Products in development include split, whole-virus inactivated and live attenuated influenza vaccines (LAIVs). Additionally, while most manufacturers propagate the virus in eggs, PATH is supporting the development of cell-based processes that could substantially increase global manufacturing capacity and flexibility. We review recent data from clinical trials of pandemic influenza vaccines manufactured in developing countries. An important discussion is on the role of whole virion vaccines for H5N1, given the poor immunogenicity of split vaccines and the complexity involved in developing potent adjuvants.     

Recombinant H7 hemagglutinin expressed in glycoengineered Pichia pastoris forms nanoparticles that protect mice from challenge with H7N9 influenza virus

Cases of H7N9 human infection caused by an avian-origin H7N9 virus emerged in eastern China in 2013, leading to the urgent requirement of developing an effective vaccine to reduce its pandemic potential. In this report, the full-length recombinant H7 protein (rH7) of A/Hangzhou/1/2013 (H7N9) virus was expressed by a glycoengineered Pichia pastoris system. The rH7 protein underwent complex glycosylation modifications and polymerized to nanoparticles of 30–50 nm in diameter. Recombinant H7 (1.9 µg) elicited a > 1:40 hemagglutination inhibition titer, and 3.75 µg rH7 protected 100% of the mice in the mice challenge model with 10-fold 50% lethal dose of the A/Shanghai/2/2013 (H7N9) rat lung-adapted strain. In conclusion, rH7 produced by the glycoengineered P. pastoris can be used for vaccination against the H7N9 virus, and provides an effective platform for the rapid production of future influenza vaccines.     

Evaluation of influenza virus-like particles and Novasome adjuvant as candidate vaccine for avian influenza

The development of safe and effective vaccines for avian influenza viruses is a priority for pandemic preparedness. Adjuvants improve the efficacy of vaccines and may allow antigen sparing during a pandemic. We have previously shown that influenza virus-like particles (VLPs) comprised of HA, NA, and M1 proteins represent a candidate vaccine for avian influenza H9N2 virus [Pushko P, Tumpey TM, Fang Bu, Knell J, Robinson R, Smith G. Influenza virus-like particles comprised of the HA, NA, and M1 proteins of H9N2 influenza virus induce protective immune responses in BALB/c mice. Vaccine 2005;23(50):5751-9]. In this study, an H9N2 VLP vaccine and recombinant HA (rH9) vaccine were evaluated in three animal models. The H9N2 VLP vaccine protected mice and ferrets from challenge with A/Hong Kong/1073/99 (H9N2) virus. Novasome adjuvant improved immunogenicity and protection. Positive effect of the adjuvant was also detected using the rH9 vaccine. The results have implications for the development of safe and effective vaccines for avian influenza viruses with pandemic potential.     

Control of pandemic (H1N1) 2009 influenza virus infection of ferret lungs by non-adjuvant-containing pandemic and seasonal vaccines

The pandemic H1N1 2009 influenza virus caused relatively mild disease in most infected people but some suffered extensively from primary lung infection, many more than would have occurred with seasonal influenza infection. Early commercially available pandemic H1N1 vaccines did not contain adjuvant, as did many of the subsequent vaccines, and could not stop infection with the pandemic virus in vaccinated ferrets. Nevertheless, we showed that virus loads in the lungs were greatly diminished in ferrets vaccinated once with an unadjuvanted pandemic vaccine and challenged with 10(6)EID(50) wildtype A/California/07/2009 (H1N1). In addition, a single inoculation with seasonal vaccine showed beneficial reduction in pandemic pulmonary virus loads in the absence of any detectable cross-reactive serological responses. Ferrets primed with either seasonal or pandemic vaccine and then boosted with pandemic vaccine also showed less extensive lung infection when challenged with a tenfold higher dose of pandemic virus. These results implicate non-classical protective mechanisms that prevent severe pulmonary disease but not viral shedding and imply that particular non-adjuvanted vaccines may have retained the ability to induce these responses.     

Evaluation of avian influenza virus isolated from ducks as a potential live vaccine candidate against novel H7N9 viruses

Recent outbreaks of a novel H7N9 avian influenza virus in humans in China raise pandemic concerns and underscore an urgent need to develop effective vaccines. Theoretically, live influenza vaccines are of multiple advantages over traditional inactivated influenza vaccines to be used in a pandemic, because they can be produced rapidly, safely, and inexpensively. However, studies on live vaccines against the novel H7N9 virus are limited. In this study, we evaluated a potential live influenza vaccine candidate using an H7N3 avian influenza virus isolated from ducks with controls of two recombinant viruses generated through reverse genetics. The potential candidate could be produced efficiently using chicken embryonated eggs, and is homogenous to the novel H7N9 virus in their viral hemagglutinin genes. The potential candidate is likely low pathogenic to birds and mammals, and likely sensitive to oseltamivir and amantadine, as suggested by its genomic sequences. Its low pathogenicity was further supported through inoculation in mice, chicken embryonated eggs and chickens. Specific antibodies elicited in mice were detectable at least during the period between day 14 and day 56 after intranasal administration of the candidate for one time. Titers of the specific antibodies increased significantly with a boost intranasal administration or a higher inoculation dose. The induced specific antibodies were of substantial cross-reactivity with the novel H7N9 virus. These primary but promising evaluation data suggest that the duck influenza virus could be used as a potential live vaccine candidate, favorably through a prime-boost route, to mitigate the severity of the possible pandemic caused by the newly emerging H7N9 virus, and is valuable to be further evaluated.     

Plant-derived hemagglutinin protects ferrets against challenge infection with the A/Indonesia/05/05 strain of avian influenza

The global spread of highly pathogenic avian influenza virus (H5N1 subtype) has promoted efforts to develop human vaccines against potential pandemic outbreaks. However, current platforms for influenza vaccine production are cumbersome, limited in scalability and often require the handling of live infectious virus. We describe the production of hemagglutinin from the A/Indonesia/05/05 strain of H5N1 influenza virus by transient expression in plants, and demonstrate the immunogenicity and protective efficacy of the vaccine candidate in animal models. Immunization of mice and ferrets with plant-derived hemagglutinin elicited serum hemagglutinin-inhibiting antibodies and protected the ferrets against challenge infection with a homologous virus. This demonstrates that plant-derived H5 HA is immunogenic in mice and ferrets, and can induce protective immunity against infection with highly pathogenic avian influenza virus. Plants could therefore be suitable as a platform for the rapid, large-scale production of influenza vaccines in the face of a pandemic.     

Analysis of the immunogenicity and bioactivities of a split influenza A/H7N9 vaccine mixed with MF59 adjuvant in BALB/c mice

The H7N9 influenza virus caused significant mortality and morbidity in humans during an outbreak in China in 2013. A recombinant H7N9 influenza seed with hemagglutinin (HA) and neuraminidase (NA) gene segments from A/Zhejiang/DTID-ZJU01/2013(H7N9) and six internal protein gene segments from A/Puerto Rico/8/34(H1N1; PR8) were generated using reverse genetics. We sought to determine the immunogenic, protective properties, and mechanisms of a split avian influenza A/H7N9 vaccine mixed with MF59 adjuvant in comparison to vaccines that included other adjuvant. BALB/c mice were vaccinated with two doses of different amounts and combinations of this novel A/ZJU01/PR8/2013 split vaccine with adjuvant. Mice were subsequently challenged with A/Zhejiang/DTID-ZJU01/2013(H7N9) by intranasal inoculation. We verified that MF59 enhanced the HI, MN, and IgG antibody titers to influenza antigens. Compared with alum, MF59 could more potentially induce humoral immune responses and Th2 cytokine production after virus infection, while both MF59 and alum can slightly increase NK cell activity. This split H7N9 influenza vaccine with MF59 adjuvant could effectively induce antibody production and protect mice from H7N9 virus challenge. We have selected this vaccine for manufacture and future clinical studies to protect humans from H7N9 virus infection.     

Pandemic influenza A/H1N1 vaccine administered sequentially or simultaneously with seasonal influenza vaccine to HIV-infected children and adolescents

In order to evaluate the immunogenicity, safety and tolerability of the 2009 A/H1N1 MF59-adjuvanted influenza vaccine administered sequentially or simultaneously with seasonal virosomal-adjuvanted influenza vaccine to HIV-infected children and adolescents, 36 HIV-infected children and adolescents, and 36 age- and gender-matched healthy controls were randomised 1:1 to receive the pandemic vaccine upon enrolment and the seasonal vaccine one month later, or to receive the pandemic and seasonal vaccines simultaneously upon enrolment. Seroconversion and seroprotection rates against the pandemic influenza A/H1N1 virus were 100% two months after vaccine administration in both groups, regardless of the sequence of administration. Geometric mean titres against pandemic and seasonal antigens were significantly higher when the seasonal and pandemic vaccines were administered simultaneously than when the seasonal vaccine was administered alone. Local and systemic reactions were mild and not increased by simultaneous administration. In conclusion, the 2009 pandemic influenza A/H1N1 MF59-adjuvanted vaccine is as immunogenic, safe and well tolerated in HIV-infected children and adolescents as in healthy controls. Its simultaneous administration with virosomal-adjuvanted seasonal antigens seems to increase immune response to both pandemic and seasonal viruses with the same safety profile as that of the pandemic vaccine alone. However, because this finding cannot be clearly explained by an immunological viewpoint, further studies are needed to clarify the reasons of its occurrence.     

Multi-antigen vaccines based on complex adenovirus vectors induce protective immune responses against H5N1 avian influenza viruses

There are legitimate concerns that the highly pathogenic H5N1 avian influenza virus could adapt for human-to-human transmission and cause a pandemic similar to the 1918 "Spanish flu" that killed 50 million people worldwide. We have developed pandemic influenza vaccines by incorporating multiple antigens from both avian and Spanish influenza viruses into complex recombinant adenovirus vectors. In vaccinated mice, these vaccines induced strong humoral and cellular immune responses against pandemic influenza virus antigens, and protected vaccinated mice against lethal H5N1 virus challenge. These results indicate that this multi-antigen, broadly protective vaccine may serve as a safer and more effective approach than traditional methods for development of a pandemic influenza vaccine.     

One-shot vaccination with an insect cell-derived low-dose influenza A H7 virus-like particle preparation protects mice against H7N9 challenge

Human infections with a novel influenza A H7N9 subtype virus were reported in China recently. The virus caused severe disease with high mortality rates and it raised concerns over its pandemic potential. Here, we assessed in the mouse model protective efficacy of single immunisations with low vaccine doses of insect cell-derived H7 virus-like particles, consisting of hemagglutinin and matrix protein. Vaccinated mice were fully protected and survived a stringent lethal challenge (100 mLD50) with H7N9, even after a single, unadjuvanted, low vaccine dose (0.03 μg). Serum analysis revealed broad reactivity and hemagglutination inhibition activity across a panel of divergent H7 strains. Moreover, we detected significant levels of cross-reactivity to related group 2 hemagglutinins. These data demonstrate that virus-like particle vaccines have the potential to induce broadly protective immunity against the novel H7N9 virus and a variety of other H7 strains.     

Protective efficacy in mice of monovalent and trivalent live attenuated influenza vaccines in the background of cold-adapted A/X-31 and B/Lee/40 donor strains

Influenza virus continues to take a heavy toll on human health and vaccination remains the mainstay of efforts to reduce the clinical impact imposed by viral infections. Proven successful for establishing live attenuated vaccine donor strains, cold-adapted live attenuated influenza vaccines (CAIVs) have become an attractive modality for controlling the virus infection. Previously, we developed the cold-adapted strains A/X-31 and B/Lee/40 as novel donor strains of CAIVs against influenza A and B viruses. In this study, we investigated the protective immune responses of both mono- and trivalent vaccine formulations in the mouse model. Two type A vaccines and one type B vaccine against A/New Caledonia/20/99 (H1N1), A/Panama/2007/99 (H3N2), and B/Shangdong/7/97 in the background of the A/X-31 ca or B/Lee/40 ca were generated by a reassortment procedure and evaluated for their immunogenicity and protective efficacy. Each monovalent vaccine elicited high levels of serum antibodies and conferred complete protection against homologous wild type virus infection. As compared to the monovalent vaccines, trivalent formulation induced higher levels of type A-specific serum antibodies and slightly lower levels of type B-specific antibodies, suggesting an immunological synergism within type A viruses and an interference in the replication of type B virus. Relatively lower type B-specific immunogenicity in trivalent vaccine formulation could be effectively implemented by increasing the vaccine dose of influenza B virus. These results of immunogenicity, protection efficacy, and immunological synergism between type A vaccines provide an experimental basis for optimal composition of trivalent vaccines for subsequent developments of multivalent CAIVs against seasonal and pandemic influenza viruses.     

A systematic review and meta-analysis of cross-reactivity of antibodies induced by oil-in-water emulsion adjuvanted influenza H5N1 virus monovalent vaccines

BackgroundCross-clade immunogenic stockpiled H5N1 vaccines may decrease the morbidity and transmission of infection during the initial phase of influenza pandemic. Meta-analysis of cross-reactive antibodies induced by oil-in-water emulsion adjuvanted (OWEA) influenza H5N1 virus monovalent vaccines with circulating heterologous H5N1 virus strains, isolated from human infections was performed.MethodsLiterature search of MEDLINE, EMBASE, Web of Knowledge, The Cochrane Library, ClinicalTrials.gov, and International Standard Randomised Controlled Trial Number registry was conducted up through December 1, 2015. Methodologically qualified studies were included for (1) use of two doses of licensed OWEA (AS03 or MF59) egg-derived, inactivated influenza H5N1 virus monovalent vaccine, (2) participant age between 18 and 64 years, and (3) evaluation of immunogenicity outcome for one or more subclade. Meta-analysis assessed the cross-reactivity of antibodies elicited by clade 1 adjuvanted vaccine strain against clade 2.1 virus strain (A/Vietnam/1194/2004 vs. A/Indonesia/05/2005); and separately against clade 2.2 virus strain (A/Vietnam/1194/2004 vs. A/turkey/Turkey/1/05); and clade 2.1 adjuvanted vaccine strain against clade 1 virus strain (A/Indonesia/05/2005 vs. A/Vietnam/1194/2004). Quantitative publication bias and influence analysis was conducted to evaluate potential impact of unpublished or new studies on the robustness of meta-analysis.ResultsOf 960 articles, 53 qualified for quality assessment and 15 studies met the inclusion criteria. All assessed clade pairs elicited cross-reactive antibodies (clade 1 against clade 2.1 and 2.2; clade 2.1 against clade 1, 2.2, and 2.3). Heterologous strains of same sub-clade are likely to elicit higher cross-reactive antibodies.ConclusionsOWEA influenza H5N1 virus monovalent vaccines exhibit broad cross-clade immunogenicity, a desired feature for vaccine stockpiling not yet demonstrated by unadjuvanted vaccines. In case of an impending H5N1 virus pandemic, stockpiled OWEA influenza H5N1 virus monovalent vaccines may allow population priming that could slow down the course of pandemic and could offer additional time needed for development of an effective strain specific vaccine supply.     

A phase I clinical trial of a PER.C6 cell grown influenza H7 virus vaccine

Avian influenza H7 viruses have transmitted from poultry to man causing human illness and fatality, highlighting the need for pandemic preparedness against this subtype. We have developed and tested the first cell-based human vaccine against H7 avian influenza virus in a phase I clinical trial. Sixty healthy volunteers were intramuscularly vaccinated with two doses of split H7N1 virus vaccine containing 12 μg or 24 μg haemagglutinin alone or with aluminium hydroxide adjuvant (300 μg or 600 μg, respectively). The vaccine was well tolerated in all subjects and no serious adverse events occurred. The vaccine elicited low haemagglutination inhibition and microneutralisation titres, although the addition of aluminium adjuvant augmented the antibody response. We found a higher number of antibody secreting cells and an association with IL-2 production in subjects with antibody response. In conclusion, our study shows that producing effective H7 pandemic vaccines is as challenging as has been observed for H5 vaccines.     

Influenza virus-like particles comprised of the HA, NA, and M1 proteins of H9N2 influenza virus induce protective immune responses in BALB/c mice

Avian influenza viruses represent a growing threat for an influenza pandemic. To develop recombinant vaccine for avian influenza of the H9N2 subtype, we expressed in insect cells virus-like particles (VLPs) consisting of three structural proteins of influenza A/Hong Kong/1073/99 (H9N2) virus. Upon infection of Sf9 cells with recombinant baculoviruses, the hemagglutinin (HA), neuraminidase (NA), and matrix (M1) proteins were co-expressed in the infected cells, self-assembled, and released into the culture medium as VLPs of 80–120 nm in diameter. VLPs exhibited functional characteristics of influenza virus including hemagglutination and neuraminidase activities. In BALB/c mice, VLPs elicited serum antibodies specific for influenza A/Hong Kong/1073/99 (H9N2) virus and inhibited replication of the influenza virus after challenge. Thus, VLPs represent a potential strategy for the development of human vaccines against avian influenza H9N2 viruses.     

An alternative method for preparation of pandemic influenza strain-specific antibody for vaccine potency determination

The traditional assay used to measure potency of inactivated influenza vaccines is a single-radial immunodiffusion (SRID) assay that utilizes an influenza strain-specific antibody to measure the content of virus hemagglutinin (HA) in the vaccine in comparison to a homologous HA reference antigen. Since timely preparation of potency reagents by regulatory authorities is challenging and always a potential bottleneck in influenza vaccine production, it is extremely important that additional approaches for reagent development be available, particularly in the event of an emerging pandemic influenza virus. An alternative method for preparation of strain-specific antibody that can be used for SRID potency assay is described. The approach does not require the presence or purification of influenza virus, and furthermore, is not limited by the success of the traditional technique of bromelain digestion and purification of virus HA. Multiple mammalian expression vectors, including plasmid and modified vaccinia virus Ankara (MVA) vectors expressing the HAs of two H5N1 influenza viruses and the HA of the recently emerging pandemic H1N1 (2009) virus, were developed. An immunization scheme was designed for the sequential immunization of animals by direct vector injection followed by protein booster immunization using influenza HA produced in vitro from MVA vector infection of cells in culture. Each HA antibody was highly specific as shown by hemagglutination inhibition assay and the ability to serve as a capture antibody in ELISA. Importantly, each H5N1 antibody and the pandemic H1N1 (2009) antibody preparation were suitable for use in SRID assays for determining the potency of pandemic influenza virus vaccines. The results demonstrate a feasible approach for addressing one of the potential bottlenecks in inactivated pandemic influenza vaccine production and are particularly important in light of the difficulties in preparation of potency reagent antibody for pandemic H1N1 (2009) virus vaccines.     

Strategies for inducing protection against avian influenza A virus subtypes with DNA vaccines

The cross-species transfer of a H5N1 influenza virus from birds to humans, and the systemic spread of this virus in mice, has accelerated the efforts to devise protective strategies against lethal influenza viruses. DNA vaccination with the highly conserved nucleoprotein gene appears to provide cross protection against influenza A viruses in murine models. Whether such vaccines would protect human hosts against different influenza A viruses, including strains with pandemic potential, is unclear. Our aim in this study is to evaluate the ability of a combination DNA vaccine consisting of two plasmids encoding the HA genes from two different subtypes and a DNA vaccine encoding the viral nucleoprotein gene from a H5 virus to induce protection against highly lethal infection caused by H5 and H7 influenza viruses in chickens. Chickens given a single dose of plasmids expressing H5 and H7 hemagglutinins protected the birds from infection by either subtype. However, birds immunized with nucleoprotein DNA and challenged with either A/Ck/Vic/1/85(H7N7) or A/Ty/Ir/1/83 (H5N8) showed definite signs of infection, suggesting inadequate immunity against viral infection. Fifty percent of the nucleoprotein DNA immunized birds survived infection by influenza A/Ty/Ir/1/83 (H5N8) virus (virus of same subtype) while 42% survived infection by influenza A/Ck/Vic/1/85/(H7N7) virus (virus of a different subtype). These studies demonstrate that immunization with DNA encoding a type-specific gene may not be effective against either homologous or heterologous strains of virus, particularly if the challenge virus causes a highly lethal infection. However, the combination of HA subtype vaccines are effective against lethal infection caused by viruses expressing any of the HA subtypes used in the combination preparation.