EFFICACY OF REPEATED ANNUAL IMMUNIZATION WITH INACTIVATED INFLUENZA-VIRUS VACCINES OVER A 5-YEAR PERIOD

Some reports have suggested that influenza virus vaccine is less effec tive in persons that have received prior annual vaccination(s) than in those receiving it for the first time. This issue was addressed by ev aluating the efficacy of annual influenza vaccinations over a 5 year p eriod in healthy adults employing commercially-available, inactivated whole-virus vaccine. Influenza vaccination had minimal effects on over all respiratory illnesses during epidemic periods. However, it reduced influenza virus shedding by an average of 38.8% and conferred protect ion against influenza virus infection during each epidemic. Some varia tion in infection rates were noted between vaccine groups given one or more than one annual immunization, and between years, but no consiste nt pattern of differences was noted in relation to number of successiv e years of vaccination. These results suggest that the current recomme ndation for annual influenza vaccination of persons at special risk of serious disease and complications is appropriate, but that continued efforts to improve the effectiveness of our prophylactic measures agai nst influenza are needed. (C) 1997 Elsevier Science Ltd.