Is there a link between autism and flu vaccines for pregnant women?
A new study in the Journal of the American Medical Association (JAMA) Pediatrics has found no association between influenza in pregnant women, flu vaccinations and the risk of a child being born with autism.
The study looked at a cohort of more than 196,000 children born in California between 2000 and 2010 and studied the incidence of flu diagnoses as well as rates of influenza vaccination and found no link between diagnoses of autism spectrum disorder (ASD) and either contracting of the flu while pregnant or receiving of the flu vaccine, although researchers found a statistically insignificant increase in ASD risk for women developing the flu during the first trimester.
“We found no association between ASD risk and influenza infection during pregnancy or influenza vaccination during the second to third trimester of pregnancy,” say the study’s authors, all of whom are affiliated with Kaiser Permanente Northern California, a managed health care consortium based in Oakland, California. “However, there was a suggestion of increased ASD risk among children whose mothers received influenza vaccinations early in pregnancy, although the association was insignificant after statistical correction for multiple comparisons.”
Experts had previously speculated that inflammation as a result of illness during pregnancy could be linked with the onset of ASD. A U.S. study earlier this year determined that pregnant mice whose immune cells were activated during severe inflammation produced an immune effector molecule called IL-17 which is thought to interfere with brain development in the developing fetus. And a 2010 study in Denmark found that women who had suffered an infection during pregnancy serious enough to require hospitalization were more likely to have a child born with autism, even though the overall risk of such remained low.
Yet, the new study’s authors assert that the overall scientific evidence has up until now been mixed, citing two other recent studies which found no connection between influenza infection during pregnancy and ASD. Likewise, the authors report that although influenza vaccination during pregnancy does appear to induce an increase in the levels of some pro- inflammatory protein signals, that effect is short-lived. “Although vaccination induces an inflammatory response during pregnancy, the magnitude and the duration of response is much lower and shorter, respectively, for influenza vaccination than viral infection,” say the study’s authors.
The researchers found that of the 196,929 cases, a total number of 2101 (1.6 per cent) of children were subsequently diagnosed with ASD, with 45,231 (23 per cent) of the mothers having received an influenza vaccination during pregnancy and 1,400 mothers having been diagnosed with influenza (0.7 per cent).
The authors believe that the findings “do not call for changes in vaccine policy or practice,” yet they do suggest the need for further study on the issue.
One in 68 children in Canada are diagnosed with ASD, reports Autism Speaks Canada, which says that the prevalence of ASD has more than doubled in the last ten years, making it the fastest growing and most commonly diagnosed neurological disorder in the country.
Autism is thought to be caused by a mix of genetic and environmental factors. A recent study in the genetic influences by researchers at McMaster University in Hamilton found that mutations of a certain protein strand in brain cells may be affecting the development of synapses in some people with autism.