Two recent studies could not rule out the possibility that H1N1 vaccination (“Swine Flu”) (“Pandemrix”) and seasonal influenza vaccination for pregnant women may be associated with autism spectrum disorder in the offspring. Now a large study by researchers at the Karolinska Institutet in Sweden has been published in the journal Internal Medicine Annalsrefutes such an association.
Autism spectrum disorder is a severe childhood neurodevelopmental disorder characterized by communication disorders, poor social skills, and repetitive behavior. The disease begins in childhood.
While some studies suggest that influenza vaccination during pregnancy protects against morbidity in both women and their offspring, the long-term risks of H1N1 vaccination during fetal life have not been studied in detail. However, two recent studies could not rule out the possibility that offspring of women who received influenza or H1N1 influenza vaccination during pregnancy, and especially in the first trimester, were at increased risk of developing autism spectrum disorder.
Professor Jonas F. Ludvigsson, pediatrician at Örebro University Hospital and professor at the Department of Medical Epidemiology and Biostatistics at the Karolinska Institutet. Photo credit: Gustav Mårtensson
Researchers at Karolinska Institutet linked the vaccination records of pregnant women from seven Swedish health regions in 2009-2010 to the Swedish Medical Birth Register and the Swedish National Patient Register to identify autism spectrum disorders in the offspring.
The importance of vaccination research
Of the 39,726 children exposed to the vaccine, 394 (cumulative incidence 1.0%) were diagnosed with an autism spectrum disorder during the six-year follow-up period, compared with 330 (1.1%) in 29,293 non-exposed children. Adjusted for potential confounders, exposure to H1N1 vaccines during fetal life was not associated with a later childhood diagnosis of autism spectrum disorder (adjusted hazard ratio = 0.95; 95% CI = 0.81-1.12). The results for vaccinations during the first trimester of pregnancy were similar.
“Our null results are important because some people have suggested that vaccinations could cause autism and the anti-vaccine movement seems to be growing in the western world,” says lead author, Professor Jonas F. Ludvigsson, pediatrician at Örebro University Hospital and professor to the Department of Medical Epidemiology and Biostatistics, Karolinska Institutet. “H1N1 vaccination was previously associated with an increased risk of narcolepsy in young people, but vaccination of pregnant women does not appear to affect the risk of developing autism spectrum disorder in the offspring.”
He continues: “Vaccine research has never been more important. Anticipation of a vaccine against COVID-19Such vaccination is likely to be offered to millions of pregnant women. While our research group did not study the effects of COVID-19 vaccines, our research on H1N1 vaccination expands current knowledge about vaccines, pregnancy, and progeny diseases in general. ”
Adjusted for other factors
Researchers adjusted their analyzes for confounding factors such as maternal smoking, height, mother’s age, and comorbidity to minimize the influence of other factors that might explain a link between vaccination and autism.
“Without taking such factors into account, so-called confounding can lead to false associations that do not reflect a real association,” adds co-author Ass. Prof. Björn Pasternak, Department of Medicine, Karolinska Institutet (Solna).
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Reference: “Immunization against influenza A (H1N1) in mothers during pregnancy and the risk of an autism spectrum disorder in the offspring: A cohort study” by Jonas F. Ludvigsson, Henric Winell, Sven Sandin, Sven Cnattingius, Olof Stephansson and Björn Pasternak, August 31, 2020, Annals of internal medicine.
DOI: 10.7326 / M20-0167
This project was supported by grants from the Swedish Research Council and the Swedish Council for Working Life and Social Research. Dr. Pasternak was supported by the Epidemiology Program of the Strategic Research Area at Karolinska Institutet and the Swedish Research Council.
Dr. Ludvigsson is coordinating a study on behalf of the Swedish IBD Quality Register (SWIBREG). This study was funded by Janssen Corporation.
