Flu vaccines given to women during pregnancy do not increase risk of autism in children, finds study
The analysis shows that 1% of babies born to women who were given the flu vaccine and 1.1% of those whose mothers did not get the vaccine had autism spectrum disorder
Flu vaccination in pregnant women does not increase the risk of autism in children, according to researchers. There are concerns that influenza vaccine exposure during pregnancy may be associated with increased risk for Autism Spectrum Disorder (ASD). Two recent studies were unable to rule out that children born to women undergoing influenza or H1N1 influenza vaccination during pregnancy, and especially during the first trimester, were at increased risk of autism spectrum disorder. Now, a large study by experts at Karolinska Institutet in Sweden refutes any such association.
Autism spectrum disorder is a severe neurodevelopmental childhood disorder characterized by impaired communication, lack of social skills and repetitive behavior. The disease has its onset in childhood. The authors found no association between maternal H1N1 vaccination during pregnancy and risk for autism spectrum disorder in children.
The findings reveal that 1% of babies born to women who were given the vaccine and 1.1% of those whose mothers did not get the vaccine had autism spectrum disorder. Further, no association was found for vaccine exposure in the first trimester and ASD or the secondary outcome, autistic disorder (AD). The findings have been published in the Annals of Internal Medicine.
"Our null findings are important since some people have suspected that vaccinations could cause autism, and the anti-vaccine movement seems to be growing in the Western world. H1N1 vaccination has previously been linked to an increased risk of narcolepsy in young people, but vaccinating pregnant women does not seem to influence the risk of autism spectrum disorder in the offspring," explains lead author, Professor Jonas F Ludvigsson, a pediatrician at Örebro University Hospital and professor at the Department of Medical Epidemiology and Biostatistics, Karolinska Institutet.
According to Ludvigsson, vaccination research has never been more important. "Anticipating a vaccine against Covid-19, millions of pregnant women are likely to be offered such a vaccination. While our research group did not study Covid-19 vaccine effects, our research on H1N1 vaccination adds to the current knowledge about vaccines, pregnancy, and offspring disease in general," he writes.
While some studies indicate that influenza vaccination during pregnancy protects against morbidity in both the woman and her child, the long-term risks of H1N1 vaccination during fetal life have not been examined in detail. A recent US study found a small increased risk for ASD in the offspring of women who received influenza vaccination during the first trimester. The proportion of H1N1 vaccine and associated risks were not reported.
For the current analysis, the team linked vaccination data in pregnant women from seven Swedish healthcare regions in 2009-2010 to the Swedish Medical Birth Register and the Swedish National Patient Register to identify autism spectrum disorder in children.
Live birth records between October 2009 and September 2010 were studied with follow-up through December 2016 to examine the risk for ASD in mothers who were vaccinated against influenza A (H1N1) during pregnancy. The researchers adjusted their analyses for such confounders as maternal smoking, height-weight, maternal age, and comorbidity in order to minimize the influence of other factors that might explain any association between vaccination and autism.
Without taking such factors into consideration, so-called confounding may create spurious associations that do not reflect a true association, explains co-author, Bjorn Pasternak, associate professor at the Department of Medicine, Karolinska Institutet.
In total, 39,726 infants were prenatally exposed to the vaccine (13,845 during the first trimester), and 29,293 were unexposed. After a mean follow-up of 6.7 years, the investigators found that ASD and AD cases were virtually the same between vaccine-exposed and unexposed children. Restricting the analysis to vaccination in the first trimester of pregnancy did not influence risk estimates for autism spectrum disorder or autistic disorder. According to the authors, these findings suggest that vaccination strategies focusing on pregnant women are safe.
"Of the 39,726 vaccine-exposed children, 394 (cumulative incidence, 1%) had a diagnosis of autism spectrum disorder during the six-year follow-up compared with 330 (1.1%) among 29,293 unexposed children. Adjusting for potential confounders, H1N1 vaccine exposure during fetal life was not associated with a later childhood diagnosis of autism-spectrum disorder Results were similar for vaccinations in the first pregnancy trimester," the study concludes.