Improvement of inactivated influenza virus vaccines.

Inactivated influenza virus vaccines (IVVs) are used for prevention of influenza and its complications. Present vaccines are immunogenic, of low reactogenicity, and protective, but protection has varied between 0% and 100%. Increasing the dose of hemagglutinin and neuraminidase antigens with purified proteins significantly increased serum and nasal antibody responses; however, trials with newer adjuvants have not shown increased serum antibody to levels comparable with those in earlier studies using oil emulsion adjuvants. IgA antibody responses in respiratory secretions were enhanced by the respiratory administration of IVVs, but IVVs by the oral route yielded varying results. IVVs appeared less effective for pandemic influenza in 1968 than in 1957. Since IVVs will be the major preventative measure for pandemic influenza in most countries, they need to be improved to provide better protection against pandemic and interpandemic influenza. Increasing the doses of hemagglutinin and neuraminidase, using adjuvants or immunomodulators, and administering IVVs by the mucosal route could improve the performance of these vaccines.