Evidence against maternal influenza as a risk factor for schizophrenia

We tested the hypothesis that second-trimester exposure to influenza is a risk factor for schizophrenia in the child. The dates of birth of Dutch schizophrenic in-patients were examined for any effect of the 1957 A2 influenza epidemic. Individuals who were in their second trimester of foetal life at the peak of the epidemic were at no greater risk of developing schizophrenia than controls. As the present study has a larger sample size than all previous European studies, and is supported by a large study in the USA, it provides strong evidence against the hypothesis that second-trimester exposure to influenza is a risk factor for schizophrenia.