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The aim of this study was to compare the kinetics and the magnitude of the humoral immune response to two different influenza vaccine formulations, whole and split virus vaccines. BALB/c mice were immunized intramuscularly with one or two doses (3 weeks apart) of 7.5, 15 or 30 mg of haemagglutinin of monovalent A/Panama/2007/99 (H3N2) split or whole virus vaccine. The two vaccine formulations induced similar kinetics of the antibody-secreting cells response; however, differences in the magnitude were observed in the spleen and bone marrow. Vaccination with whole virus vaccine generally elicited a quicker and higher neutralizing antibody response, particularly after the first dose of vaccine. The two vaccine formulations gave different immunoglobulin G (IgG) subclass profiles. Split virus vaccine stimulated both IgG1 and IgG2a antibodies suggestive of mixed T-helper 1 (Th1) and Th2 response, whereas whole virus vaccine induced mainly an IgG2a antibody response, which is indicative of a dominant Th1 response. The increased immunogenicity of whole virus vaccine in a naïve population could reduce the vaccine concentration needed to provide protective immunity.

The kinetics of the local immune response in the upper respiratory tract to parenterally administered inactivated split trivalent influenza vaccine were examined in 19 healthy subjects. Influenza virus-specific antibody-secreting cells (ASC) could be detected as early as 2 days after vaccination in peripheral blood and tonsils, with a peak at approximately 1 week after vaccination and a decline to insignificant levels after 6 weeks. Circulating ASC produced IgG, IgA, and IgM, whereas ASC in tonsils produced mainly IgA and IgM. Influenza virus-specific antibodies were predominantly IgG and IgM in serum and IgA in oral fluid; they rose after 1 week and were elevated at 6 weeks. This may indicate a secretory involvement of the anti-influenza virus response in the upper respiratory tract. Parenteral influenza vaccination induced an immediate and significant immune response in both the upper respiratory tract and peripheral blood.