The precise impact of sex, gender and pregnancy on responses to the 2009 H1N1 vaccines is not known [87] [88] [89] [90] . Data from clinical trials of seasonal influenza vaccines reveal pronounced sex differences in the rates of vaccination, antibody responses to the vaccines and adverse reactions to the vaccines and illustrate that these differences must be considered in response to the 2009 H1N1 vaccine. Seasonal influenza vaccination data further reveal that pregnant and non-pregnant women generate comparable immune responses and experience similar adverse side effects [54] .