A new study published in Tuesday’s issue of JAMA Pediatrics reputes earlier, smaller studies that hinted at an association between serious viral and maternal fever from flu and an increased risk of autism. This newest study examined health records of more than 196,929 children born at Kaiser Permanente facilities in Northern California between 2000 and 2010.
Of those children, only 1.6% had been diagnosed with autism by June 2015 – a total of 3101 children. Among their mothers, less than 1% were diagnosed with flu while pregnant, and between 23% and 38% got a flu shot during pregnancy.
The study did find a slight increase in autism if the mothers received their flu shot in the first trimester, but researchers say that could just be chance given the small numbers of children in that group.
Kaiser Permanente’s senior research scientist Lisa Croen says that the study should be reassuring to prospective mothers and recommends no changes in the vaccine policy already in place. The Centers for Disease Control and Prevention (CDC) recommends that all pregnant women get a flu shot, since flu can increase the risk of premature birth and low birth weight for the baby.
Women who are pregnant experience many changes to their immune systems, heart and lungs. Getting a flu shot can prevent the disease or lessen the symptoms while also protecting the baby against the flu during the first few months of life.
For this particular study, researchers did not look at whether the flu vaccine women received contained the preservative thimerosal. That preservative contains small amounts of ethyl mercury. In 1999 the Food and Drug Administration (FDA) recommended thimerosal be removed from vaccines given to infants as a safety measure. Multidose flu vaccines are among the few vaccines that still have thimerosal as an ingredient.
It was British doctor Andrew Wakefield who first popularized the theory that vaccines could increase autism risk when he published a paper on the subject in 1998. That paper proved to have been faked and was retracted in 2010: the same year that Dr. Wakefield lost his license to practice medicine in the U.K.
Unfortunately, the public perception that vaccines might be linked to increased autism risk has continued to affect vaccination numbers throughout Britain and the United States.