Effect of priming infection on serologic response to whole and subunit influenza virus vaccines in animals

Results from studies in humans demonstrated that the serologic responses to A/New Jersey (NJ)/76 virus vaccines varied according to the age of the vaccine and appeared to be related to previous exposure of vaccinees to the different strains and influenza A virus. Experiments in animals were therefore performed to investigate the role of previous infection on responses to A/NJ/76 virus vaccines. Mice were infected with influenza A viruses representative of the major strains (Hsw1N1, H0N1, H2N2, H3N2) and later inoculated with various doses of whole or subunit A/NJ/76 virus vaccines. Results from experiments in mice demonstrated a low antigenicity of the subunit vaccine in unprimed animals compared with that of whole-virus vaccine; however, the antigenicity of both vaccines was enhanced in mice primed by previous infection with H0 and H1 viruses. In hamsters previously infected with an H3N2 virus, however, the response to only the whole-virus vaccine was enhanced by the priming infection. The responses of the mice were qualitatively more similar to those of humans than were the responses of hamsters.