Study finds no link between autism, maternal flu vaccination during pregnancy
An accompanying editorial noted that a comprehensive and proactive approach to vaccine safety is needed now more than ever amid research into COVID-19 vaccines.
A large cohort study found no association between influenza A(H1N1)pdm09 (“swine flu”) vaccination during pregnancy and risk for autism spectrum disorders in children.
Researchers assessed live births in seven health care regions in Sweden 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 not exposed. Results of the study were published Sept. 1 by Annals of Internal Medicine.
Mean follow-up was 6.7 years in both unexposed and exposed children. During follow-up, 394 vaccine-exposed and 330 unexposed children (1.0% and 1.1%, respectively) received a diagnosis of autism spectrum disorder. In adjusted analyses, prenatal exposure to H1N1 vaccination was not associated with diagnosis on the spectrum (adjusted hazard ratio [aHR], 0.95; 95% CI, 0.81 to 1.12) or with diagnosis of autism (aHR, 0.96; 95% CI, 0.80 to 1.16). The six-year standardized cumulative incidence difference between the unexposed and exposed children was 0.04% (95% CI, −0.09% to 0.17%) for autism spectrum disorder and 0.02% (95% CI, −0.09% to 0.14%) for autism. Risk estimates did not change when the analysis was restricted to vaccination in the first trimester of pregnancy (aHRs, 0.92 [95% CI, 0.74 to 1.16] for autism spectrum disorder and 0.91 [95% CI, 0.70 to 1.18] for autism).
According to the researchers, these findings suggest that vaccination strategies focusing on pregnant women are safe. The study did have limitations, including lack of data on H1N1 influenza infection in the pregnant mothers. “If both vaccination and influenza (the latter being less common in persons undergoing vaccination) were risk factors for [autism spectrum disorder] in the offspring, we may have failed to detect an adverse effect of vaccination,” they wrote. In addition, they could not rule out residual confounding or the healthy-vaccine effect, in which mothers who are more health conscious choose vaccination.
An editorial added that a comprehensive and proactive approach to vaccine safety is needed now more than ever amid research into COVID-19 vaccines and that there is a need to evaluate the overall safety of vaccination in pregnancy. “Not surprisingly, the authors found no link [between autism and flu vaccination],” it stated. “We know that autism has a strong genetic component and that no credible science supports the belief that vaccines administered in pregnancy (or in childhood) can cause autism.”