Numerous studies reveal that haemagglutination inhibition (HAI) titres following seasonal influenza vaccination are consistently higher in women than men of comparable ages [100] [101] [102] [103] [104] , which suggests that women may be better protected against influenza disease following vaccination than are men. Women aged 18-64 years generate a more robust neutralizing antibody response following vaccination than men [102] . Pregnant women appear to have similar responses to seasonal influenza vaccines compared to non-pregnant women. The National Institutes of Health reports that 47 out of 50 (94%) pregnant women immunized with 2009 H1N1 vaccine achieved antibodies levels considered to be protective within 21 days of inoculation [105] .