Efficacy of Double Vaccination With the 2009 Pandemic Influenza A (H1N1) Vaccine During Pregnancy

OBJECTIVE: To evaluate the efficacy of double vaccination with the 2009 pandemic influenza A (H1N1) vaccine during pregnancy. METHODS: A study of the 2009 H1N1 vaccine was conducted in 128 pregnant women, who were between 8 and 32 weeks of gestation in October 2009, to monitor the immune response to vaccination and the change in antibody positivity rate and to assess the immune response. Furthermore, the study aimed to assess the changes in these parameters after the first and second vaccination, monitor the maintenance of antibody titers in maternal blood, assess antibody transfer to umbilical cord blood, and evaluate the vaccine. RESULTS: The antibody positivity rate increased from 7.2% before vaccination to 89.5% after the second vaccination. The vaccine was efficacious, producing a sufficient immune response in 90% of patients, regardless of the stage of gestation. The antibody titers were maintained until delivery, and were higher in umbilical cord blood at delivery than in maternal blood. Although the second vaccination increased the antibody titers in 27% of patients, and the antibody titers in maternal and umbilical cord blood at delivery tended to be higher in the double vaccination group than in the single, the differences were not statistically significant. CONCLUSION: Single vaccination induces sufficient immune response and transfer of immunity to the fetus in pregnant women with no pre-existing antibodies. LEVEL OF EVIDENCE: III.