2009 A/H1N1 influenza vaccination in pregnancy: uptake and pregnancy outcomes - a historical cohort study.

OBJECTIVES: To describe the uptake of 2009 A/H1N1 influenza vaccination among pregnant women and determine if vaccination was associated with adverse pregnancy outcomes.

STUDY DESIGN: A historical cohort study was performed using booking, delivery suite and neonatal unit discharge records from the Coombe Women and Infants University Hospital, Dublin, Ireland. Singleton deliveries to women pregnant before (December 2008-September 2009) and during the pandemic (December 2009-September 2010) were included. Information on vaccination status and type of vaccine was collected on admission to the delivery suite. Logistic regression analyses were used to determine maternal characteristics associated with vaccination. Pregnancy outcomes were compared for vaccinated and unvaccinated women, with adjustment for differing maternal characteristics. Outcomes included vaccination status, preterm birth, size for gestational age, neonatal intensive care admission, congenital anomalies and perinatal death.

RESULTS: Of 6894 women pregnant during the pandemic, 2996 [43.5%] reported vaccination at delivery. In the early weeks of the vaccination programme rates of over 70% were achieved. Of those vaccinated, 246 [8.2%], 1709 [57.0%] and 1034 [34.5%] were vaccinated in the first, second and third trimesters respectively. Vaccination was less likely in younger age groups, those who were not in the professional/manager/employer socioeconomic group, women from Eastern Europe, Africa and Asia/Middle East, those who reported an unplanned pregnancy, women who booked late for antenatal care and recipients of publicly-funded obstetric care. Irish nationality was associated with reporting vaccination. There was no association between vaccination during pregnancy and adverse pregnancy outcomes. Women who were vaccinated were less likely to have a preterm delivery than unvaccinated women.

CONCLUSION: 2009 A/H1N1 influenza vaccination uptake was influenced by maternal sociodemographic factors. High vaccination uptake can be achieved in a pandemic situation. Future public health campaigns should provide clear information on vaccination safety in pregnancy, ensure consistent vaccination recommendations from healthcare professionals and provide easy access to vaccination in order to optimise uptake rates in subgroups of the population who less likely to be vaccinated. There was no association between vaccination and adverse pregnancy outcomes.