LAUSR

Epidemiological studies suggest that humans who receive repeated annual immunization with influenza vaccine are less well protected against influenza than those who receive vaccine in the current season only. To better understand potential mechanisms underlying these observations, we vaccinated influenza-naive ferrets either twice, 10 months apart (repeated vaccination group; RV), or once (current season only group; CS), using a prime-boost regimen, and then challenged the ferrets with A/Hong Kong/4801/2014(H3N2). Ferrets that received either vaccine regimen were protected against influenza disease and infection relative to naive unvaccinated ferrets, but the RV group shed more virus, especially at the peak of virus shedding 2 days post infection (p < 0.001) and regained weight more slowly (p < 0.05) than those in the CS group. Qualitative, rather than quantitative, differences in the antibody response may affect protection after repeated influenza vaccination.Influenza: Repeat vaccination impairs protectionEpidemiological evidence suggests that influenza vaccination in prior years can reduce the efficacy of influenza vaccination compared to vaccine given in the current season alone. Ian A. York and colleagues of the Centers for Disease Control and Prevention, USA investigate this phenomenon using the human relevant ferret model of influenza infection. Ferrets undergoing repeat vaccination — twice 10 months apart — show quantitatively similar antibody and cell-mediated immune responses as those given a single current-season vaccination. However, qualitatively the responses elicited by the current season vaccine alone are superior — with animals showing less dramatic loss of body weight, milder fever, reduced virus shedding and quicker recovery of lymphocyte numbers. Although less protective than current-season vaccination alone, repeated vaccination offers better protection than mock vaccination.