No association between mother flu in pregnancy, increased child autism risk

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. Also, the authors could not control for other possible unmeasured mitigating factors.

"We found no association between ASD risk and influenza infection during pregnancy or influenza vaccination during the second to third trimester of pregnancy. 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. While we do not advocate changes in vaccine policy or practice, we believe that additional studies are warranted to further evaluate any potential associations between first-trimester maternal influenza vaccination and autism," the study concludes.