Reduced reaction frequencies with repeated inactivated or live-attenuated influenza vaccination

Data collected as part of a multi-year trial examining the efficacies of inactivated and live-attenuated influenza vaccines were used to evaluate the reported occurrence of post-vaccination reactions. Two cohorts were defined: (1) individuals who received the same vaccine over two consecutive years, and (2) individuals who first enrolled in year 2 of the study and received vaccine only in that year. For both vaccines there were significantly fewer reactions reported in year 2 in those subjects who were vaccinated both years. Declines were demonstrated when comparing year 1 and 2 reaction frequencies in subjects vaccinated both years, and differences were seen when comparing year 2 reaction frequencies in subjects vaccinated both years with those first vaccinated in year 2. Reaction reporting peaked on post-vaccination days 0 and 1 following receipt of the inactivated vaccine, and on day 2 following receipt of the live-attenuated vaccine.