Children born to mothers who received an influenza vaccination or had an influenza infection during the 2nd to 3rd trimester of pregnancy were not at increased risk for autism spectrum disorder (ASD), according to a study published in JAMA Pediatrics.
In an email interview with Infectious Disease Advisor, lead investigator Ousseny Zerbo, PhD, of the Division of Research at Kaiser Permanente noted that while epidemiological studies have demonstrated an immune response-mediated association between maternal infections and fever during pregnancy and an increased risk of ASD, this was the first study to investigate the association between maternal flu vaccination during pregnancy and the risk of ASD. “The underlying hypothesis was that maternal immune activation resulting from the infection or the vaccination could be associated with increased ASD risk, or that vaccination could possibly be protective,” he stated.
The dataset used for the study was a health records database from Kaiser Permanente Northern California, an integrated health care delivery organization that serves approximately 3.5 million residents (25%-30%) in metropolitan San Francisco and Sacramento and surrounding counties. The studied cohort comprised 196,929 children born at a gestational age of at least 24 weeks between 2000 and 2010. Maternal vaccination and influenza infection was determined based on an analysis of their mothers’ inpatient and outpatient health records from conception to delivery. Within the cohort, 1400 (0.7%) of mothers had received a diagnosis of influenza and 45,231 (23%) were vaccinated for influenza during pregnancy. ASD was diagnosed in a total of 3101 of the children (1.6%).
The investigators did find a slightly increased risk of ASD when mothers received an influenza vaccination in the first trimester. However, after a post-hoc statistical correction for the multiplicity of tested hypotheses, this result was found to be insignificant, indicating that it may have been the result of chance. “If influenza vaccination during the first trimester of pregnancy causes ASD, our results suggest that it would amount to 4 additional ASD cases for every 1000 women vaccinated,” the authors wrote.
“This large study is reassuring for expectant mothers. The results of this study confirm that neither getting influenza during pregnancy nor getting a flu vaccine during the 2nd and 3rd trimester are associated with risk of autism in the child,” Dr Zerbo told Infectious Disease Advisor. “We are not recommending changes in our vaccination policy, which currently is to encourage all women to be vaccinated against the flu during their pregnancy.”
Zerbo O, Qian Y, Yoshida C, Fireman BH, Klein NP, Croen LA. Association between influenza infection and vaccination during pregnancy and risk of autism spectrum disorder. JAMA Pediatr. 2016. doi: 10.1001/jamapediatrics.2016.3609