HealthDay News—The vaccine against the H1N1 strain of influenza doesn’t appear to be linked to congenital malformations, according to research published online September 20 in the Annals of Internal Medicine.

Jonas Ludvigsson, MD, PhD, of the Karolinska Institute in Stockholm, and colleagues looked at the risk of congenital malformations—overall and in terms of congenital heart disease, cleft palate, and limb abnormalities—in 40,983 children of mothers who were exposed to the H1N1 vaccine Pandemrix. The researchers compared these children to their siblings as well as to the general population.

The researchers found no sign that maternal vaccination increased the overall risk of congenital malformations in infants. The adjusted risk for congenital malformation was 4.98% and 4.96% in exposed and unexposed offspring, respectively (risk difference, 0.02%). The corresponding risk differences were 0.16% for vaccination during the first trimester and 0.10% for vaccination in the first 8 weeks.

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“When intrafamilial factors were taken into consideration, H1N1 vaccination during pregnancy did not seem to be linked to overall congenital malformation in offspring, although risk increases for specific malformations could not be ruled out completely,” the authors write.

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Ludvigsson JF, Strom P, Lundholm C, et al. Risk for congenital malformation with H1N1 influenza vaccine: A cohort study with sibling analysis. Ann Intern Med. 2016; doi: 10.7326/M16-0139