Flu vaccination during pregnancy does not up risk for ASD in offspring

Maternal influenza A/H1N1 immunization during pregnancy is not associated with an increased risk for autism spectrum disorder (ASD) in the offspring, results of a large cohort study have shown.

Nationwide registers in Sweden were used in this population-based cohort study. The investigators identified live births between October 2009 and September 2010, with follow-up through December 2016. A total of 39,726 infants were prenatally exposed to H1N1 vaccine (13,845 during the first trimester) and 29,293 infants were unexposed.

Hazard ratios (HRs) for the primary outcome, ASD, before and after adjustment for potential confounders were estimated using Cox regression. Autistic disorder (AD) was the secondary outcome.

During a mean follow-up of 6.7 years, 394 (1.0 percent) vaccine-exposed and 330 (1.1 percent) unexposed children had a diagnosis of ASD. Adjusted analyses showed no association between prenatal exposure to H1N1 vaccination and a later diagnosis of ASD (adjusted HR, 0.95, 95 percent confidence interval [CI], 0.81–1.12) or AD (adjusted HR, 0.96, 95 percent CI, 0.80–1.16).

Between unexposed and exposed children, the 6-year standardized cumulative incidence difference was 0.04 percent (95 percent CI, –0.09 percent to 0.17 percent) for ASD and 0.02 percent (95 percent CI, –0.09 percent to 0.14 percent) for AD.

Restricting the analysis to vaccination in the first trimester of pregnancy did not affect risk estimates for ASD (adjusted HR, 0.92, 95 percent CI, 0.74–1.16) and AD (adjusted HR, 0.91, 95 percent CI, 0.70–1.18).

This study was limited by lack of data on H1N1 influenza infection, according to the investigators.