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Pandemic vaccination during pregnancy: safety of the MF59 adjuvanted A/H1N1 vaccine

It has been assessed the risk of maternal, fetal, and neonatal outcomes associated with the administration of an MF59 adjuvanted A/H1N1 vaccine during pregnancy.

The trial was conducted in singleton pregnancies of the resident population of the Lombardy region of Italy, and involved all deliveries between 1 October 2009 and 30 September 2010.
Data on exposure to A/H1N1 pandemic vaccine, pregnancy, and birth outcomes were retrieved from regional databases.
Vaccinated and non-vaccinated women were compared in a propensity score matched analysis to estimate risks of adverse outcomes.

Main maternal outcomes included type of delivery, admission to intensive care unit, eclampsia, and gestational diabetes; fetal and neonatal outcomes included perinatal deaths, small for gestational age births, and congenital malformations.

Among the 86 171 eligible pregnancies, 6246 women were vaccinated ( 3615 [ 57.9% ] in the third trimester and 2557 [ 40.9% ] in the second trimester ).

No difference was observed in terms of spontaneous deliveries ( adjusted odds ratio, aOR=1.02, 95% confidence interval 0.96 to 1.08 ) or admissions to intensive care units ( aOR=0.95, 0.47 to 1.88 ), whereas a limited increase in the prevalence of gestational diabetes ( aOR=1.26, 1.04 to 1.53 ) and eclampsia ( aOR=1.19, 1.04 to 1.39 ) was seen in vaccinated women.

Rates of fetal and neonatal outcomes were similar in vaccinated and non-vaccinated women.

A slight increase in congenital malformations, although not statistically significant, was present in the exposed cohort ( aOR=1.14, 0.99 to 1.31 ).
The findings add relevant information about the safety of the MF59 adjuvanted A/H1N1 vaccine in pregnancy.
Residual confounding may partly explain the increased risk of some maternal outcomes.
Meta-analysis of published studies should be conducted to further clarify the risk of infrequent outcomes, such as specific congenital malformations. ( Xagena )

Trotta F et al, BMJ 2014;348:g3361