No abstract

Novel strategies are required to provide rapid vaccine coverage in the event of an influenza pandemic. A phase I/II dose finding/formulation study was performed with a whole-virus H5N1 clade 1 A/Vietnam vaccine (2-dose priming regimen) to evaluate safety and immunogenicity. Seventy-seven of 141 subjects in this study received a booster (12-17 months after priming) with a 7.5-microg dose of a clade 2.1 A/Indonesia vaccine. The prime-boost regimen resulted in antibody responses against clade 1, 2.1, 2.2, and 2.3 viruses that were significantly higher than those after the priming regimen. These findings demonstrate that a prime-boost regimen may alleviate vaccine supply constraints in a pandemic.

No abstract

NCT01052402.

dStudies on candidate pandemic vaccines against avian influenza viruses have focused on H5N1, but viruses of other subtypes, such as A/H9N2, are also considered to have pandemic potential. We investigated the safety and immunogenicity of two immunizations with one of five different antigen doses (ranging from 3.75 to 45 g of hemagglutinin antigen) of a nonadjuvanted whole-virus G9 lineage H9N2 influenza virus vaccine in healthy adults aged 18 to 49 years. The antibody responses were measured by hemagglutination inhibition (HI), microneutralization (MN), and single radial hemolysis (SRH) assays. To investigate a hypothesis that previous exposure to H2N2 viruses in subjects born in or before 1968 might prime for more robust antibody responses to H9N2 vaccination than that in subjects born after 1968, a post hoc age-stratified analysis of antibody responses was done. Both vaccinations in all dose groups were safe and well tolerated. No vaccine-related serious adverse events were reported, and the majority of the adverse reactions were rated as mild. The rates of injection site reactions were lower in the 3.75-g-and 7.5-g-dose groups than those in the higher-dose groups; the rates of systemic reactions were similar across all dose groups. The seroprotection rates among the different dose groups 21 days after the second immunization ranged from 52.8% to 88.9% as measured by HI assay, from 88.7% to 98.1% or 82.7% to 96.2% as measured by MN assay (MN titer cutoffs, 1:40 and 1:80, respectively), and from 94.2% to 100% as measured by SRH assay. Higher antibody responses were not induced in subjects born in or before 1968. These data indicate that a nonadjuvanted whole-virus H9N2 vaccine is well tolerated and immunogenic in healthy adults. (This study has been registered at ClinicalTrials.gov under registration no. NCT01320696.) A number of avian influenza virus subtypes have caused zoonotic infections in humans, including those of subtypes H5N1 (1), H9N2 (2), and, most recently, H7N9 (3) and H10N8 (4). Because the human population is largely immunologically naive to such viruses, there are concerns that a pandemic situation might occur if any of these viruses gains the capacity for efficient human-to-human transmission. The development of candidate pandemic vaccines to counter the threat of a pandemic resulting from avian influenza viruses is thus an important part of global pandemic preparedness programs (5, 6). To date, this effort has been concentrated largely on the development of candidate pandemic vaccines based on influenza viruses of the H5N1 subtype. A number of clinical studies have demonstrated whole-virus inactivated H5N1 vaccines to be immunogenic in adult, elderly, and pediatric populations without a requirement for adjuvantation (7-11). In the present study, we extend the clinical investigation of nonadjuvanted whole-virus avian influenza vaccines to include a vaccine against the H9N2 influenza virus subtype, which is enzootic in poultry across the Middle East and Asia and is considered to have pandemic po...