Pandemic flu vaccine in pregnancy did not cause pregnancy loss

There is no evidence of increased risk of fetal death following vaccination against the 2009 pandemic flu strain in pregnancy. This is the conclusion of a nationwide cohort study of more than 50,000 pregnant women in Denmark. The study was conducted by Danish researchers from the Department of Epidemiology Research, Statens Serum Institut, and published in the prestigious British Medical Journal.

Little information on vaccine safety in pregnancy

To protect pregnant women and unborn children, pandemic flu (H1N1) vaccination was recommended in pregnancy during the 2009 pandemic. It has been estimated that at least 322 000 pregnant women were vaccinated against pandemic influenza in Europe and that approximately 2.4 million pregnant women were vaccinated in the United States. Despite the large number of women vaccinated in pregnancy, no previous study has addressed the safety of the vaccine in this population.

Sneezing woman

Person with the flu

The new Danish study

The Danish researchers linked information from nationwide health registries on vaccination and adverse pregnancy outcomes. A total of 50 585 pregnant women were included in the study; of these, 7062 (13%) had been vaccinated against pandemic influenza. The study found no significantly increased risk of fetal death among pregnant women vaccinated with the pandemic influenza vaccine. Fetal death was defined as spontaneous abortions early in pregnancy and stillbirths later in pregnancy.

Reassuring news

The Danish study is the first to address this important issue and brings reassurance to previously pregnant women and health professionals that the pandemic flu vaccination is unlikely to have caused pregnancy losses. A number of different vaccines were used during the 2009 pandemic. The vaccine used in Denmark was commonly used throughout Europe and comparable vaccines were used in countries such as the US, meaning that the results from Denmark are relevant for many of the countries that employed vaccination in 2009.

Read the scientific article

Pasternak B, Svanström H, Mølgaard-Nielsen D, Krause TG, Emborg HD, Melbye M. Vaccination against pandemic A/H1N1 2009 influenza in pregnancy and risk of fetal death: cohort study in Denmark. BMJ 2012;344:e2794

The first author was supported by a postdoc grant (no 11-115854) from the Danish Medical Research Council.

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Department of Epidemiology Research
Björn Pasternak

Tel: +45 3268 8150