Kinetics of humoral antibody response to trivalent inactivated split influenza vaccine in subjects previously vaccinated or vaccinated for the first time.

We studied differences in immune responses after first time immunization with a trivalent inactivated split influenza vaccine, or after vaccination in the preceding year, in 42 healthy volunteers (40 +/- 13 years). Sequential serum samples were collected over 40 weeks. Previously vaccinated volunteers exhibited 40-92% protective antibody levels in their prevaccination sera. Subjects vaccinated for the first time had higher response rates and meanfold antibody increases than those vaccinated previously. Both groups had protective antibody titres 59% 7 days after vaccination and 70% of vaccinees maintained protective antibody titres after 280 days. The results corroborate earlier findings on the rapid immune response and may have a bearing on future vaccination policy.