Pandemic A/H1N1 influenza vaccination during pregnancy: a comparative study using the EFEMERIS database.

Objective: To evaluate the risk of adverse pregnancy outcomes following A/H1N1 vaccination in pregnant women.

Methods: This observational cohort study compared vaccinated and non-vaccinated pregnant women in EFEMERIS, a French prescription database including pregnant women. Women who ended their pregnancy in South Western France between October 21, 2009 and November 30, 2010 (the period of the French vaccination campaign) were included. Two non-vaccinated women were individually matched to each vaccinated woman by month and year of pregnancy onset. Conditional logistic regression and Cox proportional hazards regression were used to evaluate associations between each outcome (all-cause pregnancy loss, preterm delivery, small for gestational age (SGA) and neonatal pathology) and A/H1N1 vaccination during pregnancy.

Results: 1645 women of the 12,120 (13.6%) in the database who were administered A/H1N1 vaccine during pregnancy were compared to 3290 non-vaccinated women. Most were vaccinated in December 2009 (61%) with a non-adjuvanted vaccine (93%). The risks of pregnancy loss (adjusted HR=0.56; 95% CI=0.31-1.01), of preterm birth (adjusted HR=0.82; 95% CI=0.64-1.06), and of neonatal pathology (adjusted OR=0.70; 95% CI=0.49-1.02) did not differ between the vaccinated and the non-vaccinated groups. The rate of SGA was lower in the vaccinated group than in the non-vaccinated group (0.5% vs. 1.4%; adjusted OR=0.36; 95% CI=0.17-0.78).

Conclusion: There was no significant association between adverse pregnancy outcomes and vaccination with a non-adjuvanted A/H1N1 vaccine during pregnancy.