The effect of sex on responses to influenza vaccines.

The poor uptake and limited effectiveness of seasonal influenza vaccines mean that influenza continues to create a significant burden of disease. It has been hypothesized that sex differences are present in responses to seasonal influenza vaccines, and that these differences may contribute to this poor vaccine success. This has led to the suggestion that vaccines should be tailored to an individual's biological sex. However, studies in this field are often low quality. Comprehensive analysis of the available literature reveals that there is insufficient evidence to support sex differences in vaccine immunogenicity, effectiveness, or efficacy. Nonetheless, differences in vaccine safety are consistently observed, with females reporting adverse events following immunization more frequently than males. Bias introduced by gender differences in passive reporting of adverse effects may underlie this phenomenon. Highly controlled studies are required in future before any conclusions can be made about potential sex differences in response to seasonal influenza vaccines.