Influenza (H1N1) vaccination during pregnancy not associated with autism

Reference

Ludvigsson JF, Winell H, Sandin S, et al. Maternal influenza A(H1N1) immunization during pregnancy and risk for autism spectrum disorder in offspring. A cohort study. Ann Intern Med 2020;173(8):597-604.

Synopsis

This study was conducted on infants who were in utero during the 2009 influenza pandemic in which the A(H1N1)pdm09 ("swine flu") vaccine was offered at no charge to all pregnant women (and others) in Sweden. Using the national birth registry, the researchers identified 39,726 infants exposed to the vaccine, including 13,845 in the first semester. They also followed 29,293 infants of mothers who didn't receive the vaccine. During a mean follow-up of 6.7 years, 394 (1.0%) of exposed children and 330 (1.1%) of unexposed children had a diagnosis of autism spectrum disorder. Prenatal exposure to the vaccine was not associated with a later diagnosis of either autism spectrum disorder or autistic disorder, even when looking just at children exposed in the first trimester. This was not a randomized study and it was performed during a single influenza season with a single vaccine.