A big concern nowadays is why some children develop autism, specifically autism spectrum disorder (ASD). Autism spectrum disorder is considered a life-long neurodevelopmental disorder that is thought to affect 1 out of 68 American children. While the causes of ASD are unknown in most cases, some studies report an association (higher risk) between a pregnant woman's infections and fever during pregnancy and risk of ASD in the baby, while other studies don't find such an association. Some studies also looked at the timing of infections during pregnancy, but again results have been mixed. A viral infection during the first trimester is associated with increased risk in some studies, while other studies report an increased risk with a second- or third-trimester bacterial infection. So it has been unclear whether a flu (influenza) infection or flu vaccination during pregnancy is linked to autism spectrum disorder or not. Is there a link or not?
Why are pregnant women encouraged to get a flu shot (flu vaccine)? This is because pregnant women have an increased risk of complications from the flu infection. Studies also show that getting a flu vaccine during pregnancy reduces the risk of a preterm birth, a small-for gestational-age child, and a low-birth-weight child, and prevents influenza infection in newborns for up to 6 months.
The researchers of a large study done in California found no association between autism spectrum disorder (ASD) risk and flu (influenza) infection during pregnancy or flu (influenza) vaccination during the second to third trimester of pregnancy. However, there was a suggestion of increased ASD risk among children whose mothers received flu vaccinations during the first trimester (though the researchers say the association was perhaps due to "chance". Bottom line: the study results were reassuring for pregnant women, but if one wanted to be ultra-cautious, then delay getting a flu shot until the second trimester of pregnancy. From Science Daily:
A study of more than 196,000 children found no association between a mother having an influenza infection anytime during pregnancy and an increased risk of autism spectrum disorders (ASDs) in children, according to a new study published online by JAMA Pediatrics. The study by Ousseny Zerbo, Ph.D., of Kaiser Permanente Northern California, Oakland, and coauthors included 196,929 children born in the health system from 2000 through 2010 at a gestational age of at least 24 weeks.
Within the group, there were 1,400 mothers (0.7 percent) diagnosed with influenza and 45,231 mothers (23 percent) who received an influenza vaccination during pregnancy. There were 3,101 children (1.6 percent) diagnosed with ASD. The authors report no association between increased risk of ASD and influenza vaccination during the second and third trimesters of pregnancy. There was a suggestion of increased risk of ASD with maternal vaccination in the first trimester but the authors explain the finding was likely due to chance because it was not statistically significant after adjusting for multiple comparisons. The study cannot establish causality and has several limitations, including ASD status determined by diagnoses on medical records and not validated by standardized clinical assessment for all cases. [Original study.]