BOSTON (CBS) — A new study has found “reassuring” evidence that H1N1 flu vaccine is safe during pregnancy.

The national study was launched shortly after the H1N1 outbreak in 2009 and was led by Boston University, UC San Diego in collaboration with the American Academy of Allergy Asthma and Immunology.

The results will be published online in the journal, “Vaccine.”

Despite the recommendation that all pregnant women should get a flu shot, it is estimated fewer than 50-percent of women actually do.

Researchers say that’s because women are concerned about the effects of the shot on the developing baby.

Researchers from Boston University, interviewed 4,191 mothers from four regional centers in the U.S. who had either delivered a baby with one of 41 specific birth defects or delivered an infant without defects.

They compared the use of the flu vaccine in the two groups during the 2009 – 2011 seasons.

Dr. Carol Louik, ScD, lead investigator of the BU team said there was no evidence of negative effects from the shot.

“We found no evidence of an increase in risk for the most commonly occurring specific major birth defects, which were the focus of the study, if a woman received the flu shot in pregnancy. Concerns about the risk of specific birth defects was a critical question that has not been considered very much until now, and our data are reassuring.”

The team also compared the risk of preterm delivery in vaccinated versus unvaccinated women.

While the team did observe a slight increase in preterm delivery rates who received the H1N1 vaccine specifically during the 2009 – 2010 season, vaccinated women overall only delivered an average of two days earlier compared to the unvaccinated group. For those vaccinated during the 2010 – 2011 season, the situation was reversed, and vaccinated women were less likely to deliver a preterm baby.


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