Our objective is to examine the risk for ASD in offspring of mothers who were vaccinated against influenza A(H1N1)pdm09 (“swine flu”) during pregnancy

The participants- live births between October 2009 and September 2010, with follow-up through December 2016. In total, 39 726 infants were prenatally exposed to the H1N1 vaccine (13 845 during the first trimester) and 29 293 infants were unexposed.

Cox regression was used to estimate hazard ratios (HRs) for the primary outcome, ASD, before and after adjustment for potential confounders. The secondary outcome was autistic disorder (AD).

The mean follow-up was 6.7 years in both unexposed and exposed children. During follow-up, 394 (1.0%) vaccine-exposed and 330 (1.1%) unexposed children had a diagnosis of ASD. In adjusted analyses, prenatal exposure to H1N1 vaccination was not associated with a later diagnosis of ASD (adjusted HR [aHR], 0.95 [95% CI, 0.81 to 1.12]) or AD (aHR, 0.96 [CI, 0.80 to 1.16]). The 6-year standardized cumulative incidence difference between the unexposed and exposed children was 0.04% (CI, −0.09% to 0.17%) for ASD and 0.02% (CI, −0.09% to 0.14%) for AD. Restricting the analysis to vaccination in the first trimester of pregnancy did not influence risk estimates (aHR, 0.92 [CI, 0.74 to 1.16] for ASD and 0.91 [CI, 0.70 to 1.18] for AD).

This large cohort study found no association between maternal H1N1 vaccination during pregnancy and risk for ASD in the offspring.

Ref: https://www.acpjournals.org/doi/10.7326/M20-0167