The PREGVAXGRIP study: a cohort study to assess foetal and neonatal consequences of in utero exposure to vaccination against A(H1N1)v2009 influenza.

Background: In October 2009, in the context of an A(H1N1)v2009 influenza pandemic, a vaccination campaign was launched in France, in which one of the priority groups was pregnant women, on account of the high risk of developing complications following infection by this virus.

Objective: The aim of this multicentric, prospective, observational study was to assess safety and pregnancy outcomes in a cohort of pregnant women when receiving the A(H1N1)v2009 influenza pandemic vaccine.

Methods: This was a prospective study that followed up pregnant women recruited mainly in vaccination centres and maternity departments. Following the expected delivery date, follow-up data were collected concerning the delivery, the infant, and, if appropriate, the reasons why the pregnancy did not reach its term.

Results: Between 1 November 2009 and 31 March 2010, 2,415 pregnant women were included at the time of vaccination; 97.6 % of women received a vaccine without adjuvant and 2.4 % received an adjuvanted vaccine. Ninety-two (3.9 %) women were vaccinated during the first trimester of pregnancy, 1,090 (46.5 %) during the second trimester, and 1,162 (49.6 %) during the third trimester. One hundred and thirty-three adverse events (5.5 % of women) were reported, of which 12 were unexpected or serious. There were 2,246 (93.0 %) known pregnancy outcomes with 12 spontaneous abortions (0.5 %), 6 stillbirths (0.3 %), and 4 therapeutic abortions (0.2 %). There were 65 neonates with congenital anomalies, among which 31 were major. But only one congenital malformation (1.4 %) was reported for the 92 women vaccinated in their first trimester. Of the women, 93.3 % were delivered full term and 6.7 % preterm. For 96 (4.2 %) neonates, a disorder was reported in the neonatal period and 130 (5.6 %) were transferred to the neonatology department.

Conclusions: This study suggests that exposure to the A(H1N1)v2009 pandemic influenza vaccine during pregnancy does not increase the risk of adverse pregnancy outcomes. However, because of the relatively small number of women exposed during the first trimester, other studies are needed to exclude an increased risk of malformation.