A large binational study of more than 2.7 million mother-child pairs found that maternal influenza infection during pregnancy was associated with a small increase in the risk of any neuropsychiatric disorder in children in standard population-level analyses. However, when the researchers compared siblings born to the same mother, the association disappeared in both the South Korean discovery cohort and the Japanese replication cohort.
The population-level association was driven mainly by attention deficit-hyperactivity disorder and obsessive-compulsive disorder in the Korean cohort, and by ADHD in the Japanese cohort. No significant links were seen for autism spectrum disorder, intellectual disability, or severe neuropsychiatric disorders in either cohort. The sibling comparisons, which help control for shared family environment and genetic factors, showed no significant relationship between maternal flu and any of the five neuropsychiatric disorders studied.
The researchers caution that the sibling analyses had smaller samples and wider confidence intervals, so they should not be read as definitive proof of no association. They also note follow-up ended in childhood or early adolescence, and unmeasured confounding cannot be ruled out. The findings should not change current guidance: flu vaccination is recommended during pregnancy, and the authors say the results should not cause unnecessary anxiety for expectant mothers.