• Lisa A Jackson, Shital M Patel, Geeta K Swamy, Sharon E Frey, C Buddy Creech, Flor M Munoz, Raul Artal, Wendy A Keitel, Diana L Noah, Carey Rodeheffer Petrie, Mark Wolff, and Kathryn M Edwards.
• The Group Health Research Institute, Group Health, Seattle, Washington, USA. jackson.l@ghc.org
• J. Infect. Dis. 2011 Sep 15;204(6):854-63.

BackgroundAlthough pregnant women are at increased risk of severe illness following influenza infection, there is relatively little information on the immunogenicity of influenza vaccines administered during pregnancy.MethodsWe conducted a clinical trial that enrolled 120 pregnant women in which participants were randomly assigned to receive an inactivated 2009 H1N1 influenza vaccine containing either 25 μg or 49 μg of hemagglutinin (HA) in a 2-dose series with a 21-day period between administration of the first and second doses.ResultsFollowing the first vaccination, HA inhibition (HAI) titers of ≥1:40 were detected in 93% (95% confidence interval [CI], 82%-98%) of subjects who received the 25-μg dose and 97% (95% CI, 88%-100%) of subjects receiving the 49-μg dose. In cord blood samples, HAI titers of ≥1:40 were found in 87% (95% CI, 73%-96%) of samples from the 25-μg dose group and in 89% (95% CI, 76%-96%) from the 49-μg dose group. Microneutralization titers tended to be higher than HAI titers, but the patterns of response were similar.ConclusionsIn pregnant women, 1 dose of an inactivated 2009 H1N1 influenza vaccine containing 25 μg of HA elicited an antibody response typically associated with protection against influenza infection. Efficient transplacental transfer of antibody was also documented.

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