During the 2009 H1N1 pandemic, several million pregnant women in the United States and more than 300,000 in Europe were vaccinated. A new study looked at whether that led to complications in their babies.
For pregnant women in the United States a flu shot has been recommended since 2004. But the 2009 H1N1 pandemic was the first time that flu vaccination was recommended for pregnant women in many European countries.
In Denmark, high-risk expectant mothers were advised to get flu shots anytime during pregnancy. Researchers say vaccination was much more common in the 2nd and 3rd trimester of pregnancy and relatively uncommon in the first trimester
The investigators identified all infants born in Denmark between November 2009 and September 2010. Then, they compared infants and mothers who had vaccine exposure to those who did not.
Of the 50,000 infants and their mothers, 7000 had vaccine exposure, about 13 percent. Researchers say they found no increase in birth defects, premature birth or smaller size in babies whose mom's had been vaccinated.
"We can conclude that the vaccine was relatively safe in pregnancy," said lead researcher Bjrn Pasternak, M.D., Ph.D., of the Statens Serum Institut, Copenhagen, Denmark.
This is the largest study to look at the safety of the H1N1 vaccine in pregnant women. Researchers say further study is needed to address risk of specific birth defects and the effectiveness of H1N1 vaccination in pregnancy.