H1N1 Vaccine Safe for Pregnant Women

H1N1 flu vaccine didnt lead to poorer outcomes among babies of vaccinated pregnant women

/ Author:  / Reviewed by: Robert Carlson, M.D

(RxWiki News) There are several vaccines pregnant women are advised to get and several others they should avoid while pregnant. The flu vaccine is one pregnant women should consider.

During 2009, this recommendation included both the normal seasonal flu vaccine, as well as the vaccine for the H1N1 strain of the flu.

A recent study from Denmark has shown that the H1N1 vaccine did not lead to any increased risk of poor outcomes for the babies of mothers who took it during pregnancy.

"Be sure to get the flu vaccine."

In a study, led by Björn Pasternak, MD, PhD, of the Department of Epidemiology Research at the Statens Serum Institut in Copenhagen, Denmark, researchers looked at whether women who received the H1N1 vaccine while pregnant had a higher risk of having negative outcomes with their babies.

The study group started with a registry including 53,432 single children (not twins, triplets, etc.) born between November 2, 2009 and September 30, 2010. Of the group, 6,989 were born to women who received the vaccine during pregnancy.

The researchers looked at the babies whose mothers were vaccinated in two groups: those mothers who had received the vaccine during the first trimester and those who received it in the second or third trimester.

They compared the rates of major birth defects, early delivery and fetal growth restriction, which means a baby was not able to reach its appropriate full size before birth.

For the first group, the researchers randomly selected 330 babies who had not been exposed to the vaccine, and compared them with similar demographics and characteristics of 330 babies who had been exposed to the vaccine in the first trimester.

In the group with first-trimester exposure to the vaccine, 18 babies had a major birth defect, compared to 15 babies in the unexposed group - a difference that is not significant enough to establish that the vaccine had any influence on birth defects.

Among those whose mothers received the vaccine in the first trimester, 31 were born early compared to 24 born early in the unexposed group.

Among 6,543 babies whose mothers received the vaccine in the second or third trimester, there were 302 preemies, compared to 295 preemies in a group of 6,366 babies whose mothers did not receive the vaccine at all.

Neither of these rates was regarded as significantly different for the two populations.

Finally, the researchers also found no link between H1N1 flu vaccination of the mother and babies who did not reach their full size.

Fetal growth restriction occurred in 25 of the infants exposed to first-semester vaccination versus 31 of the 330 babies not exposed to the vaccine.

The second- and third-trimester exposure babies included 641 with fetal growth restriction compared to 657 among the unexposed babies.

"This nationwide cohort study in Denmark found no significant associations between exposure to an AS03-adjuvanted influenza A(H1N1)pdm09 vaccine in pregnancy and risk of adverse fetal outcomes including major birth defects, preterm birth, and growth restriction," the authors concluded.

The authors noted, however, that the first-trimester vaccine exposure data should be considered preliminary and needs further confirmation because of the small study group numbers.

"Further research also needs to address risk of specific birth defects as well as effectiveness of H1N1 vaccination in pregnancy," the authors wrote.

The researchers note that approximately 2.4 million pregnant women were vaccinated against the H1N1 strain of the flu in 2009 even though there was not much data available regarding its safety for the unborn babies.

The study was published July 11 in JAMA. The research was funded by the Danish Research Council, and the authors reported no conflicts of interest.

Reviewed by: 
Review Date: 
July 8, 2012
Last Updated:
November 19, 2012