Adjuvanted A/H1N1 (2009) influenza vaccination during pregnancy: description of a prospective cohort and spontaneously reported pregnancy-related adverse reactions in the Netherlands

Background: During influenza pandemics, pregnant women have an increased risk of severe complications. Vaccination can diminish these complications. In the Netherlands, the adjuvanted vaccines Focetria® and Pandemrix® were used during the A/H1N1 (2009) influenza pandemic. The national vaccination scheme included pregnant women, but knowledge concerning the safety of adjuvants during pregnancy was lacking. The aim of the study is to assess safety of adjuvanted influenza vaccines during pregnancy.
Methods: The Dutch Teratology Information Service, part of the Netherlands Pharmacovigilance Centre Lareb, recruited 295 A/H1N1 (2009) vaccinated pregnant women through health care providers. Questionnaires were sent during the pregnancy to their health care providers and a second one 6 weeks after the estimated date of birth. Reported complications and adverse outcomes were compared with background rates. Additionally, the spontaneously reported pregnancy-related adverse reactions in the database of the Netherlands Pharmacovigilance Centre Lareb are described.
Results: Compared with the background rate, no increased risk of spontaneous abortions or congenital malformations was observed. There were three spontaneous abortions among 23 first trimester exposures. In the cohort of 281 pregnancies with known outcomes, three major malformations were observed after exposure at any time during pregnancy. In these cases exposure occurred once periconceptional, and twice in the second trimester. Furthermore, no increased risk of adverse pregnancy outcomes or neonatal problems were observed. The spontaneously reported pregnancy-related adverse events showed no unexpected pattern.
Conclusion: The present study adds further reassurance for the safe use of adjuvanted vaccines during pregnancy and facilitates decision making in future pandemics.