Swine Flu Vaccination During Pregnancy Doesn't Cause Autism Either

There are understandable concerns as to whether vaccinations are safe during pregnancy. However, new research indicates there is no link to autism in children whose mothers were vaccinated, even in the first trimester. Africa Studio/Shutterstock.com

Study after study has shown there is no link between infant vaccinations and autism. Although most anti-vaccination campaigners refuse to accept this fact, a few have moved on, claiming a less direct connection. According to this version, swine flu vaccination during pregnancy triggers autism in the child (something they appear to consider much worse than dying from the disease the vaccine prevents). Now a new peer-reviewed study shows this supposed link doesn't hold up either.

Pregnancy is obviously a bad time to get influenza, particularly in a year where circulating strains are unusually dangerous. However, ever since the thalidomide disaster in the 1960s, there is a legitimate concern that something confirmed safe for everyone else might pose a danger to a developing fetus, leaving many pregnant women unsure whether or not to get vaccinated.

Professor Jonas Ludvigsson of Sweden's Karolinska Institute compared almost 40,000 children whose mothers were vaccinated against the “swine flu” H1N1 influenza during pregnancy in 2009-10 with more than 29,000 whose mothers were not.

The results make clear that if there are any consequences from the vaccination, they are either for something rarer or harder to measure than an autism spectrum disorder (ASD) diagnosis. In Annals of Internal Medicine, Ludvigsson reports that 1 percent of the children whose mothers were vaccinated against influenza were diagnosed with ASD by the age of six. For those whose mothers were not vaccinated, the figure was 1.1 percent. Controlling for confounding factors like the mother's age or whether she smoked did not change the outcome. No matter how you slice it, autism was not higher among children whose mothers got vaccinated.

Ludvigsson also found no difference when the focus was narrowed just to women who were vaccinated during the first trimester, nor for autism disorder, the most common form of ASD. The finding is particularly significant because previous studies have contradicted each other in regards to safety in the first trimester.

"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," Ludvigsson said in a statement. "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."

Although the 2009-2010 swine flu epidemic resulted in a similar number of deaths worldwide to ordinary seasonal flu outbreaks, it posed more of a threat to children and women in late pregnancy, leading to higher vaccination rates.

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