Schizophrenia following in utero exposure to the 1957 influenza epidemics in Japan

OBJECTIVE: Studies in Finland, England, and Denmark have reported that individuals exposed to the 1957 A2 influenza pandemic during their second trimester in utero are at greater risk for later schizophrenia. However, other studies in England, the United States, and Holland reported no such association. The authors' goal was to shed light on these conflicts. METHOD: They compared the number of individuals who later developed schizophrenia who were born in the 5 months after the peak prevalence of three distinct 1957 influenza epidemics in Japan with the mean number of individuals who later developed schizophrenia who were born in the corresponding months of the 4 years surrounding the epidemics. RESULTS: A significantly greater number of females but not males who later developed schizophrenia were born during the risk exposure months than in the non-risk-exposure months. CONCLUSIONS: These findings, although weak, lend support to the claim that in utero exposure to influenza epidemics is a risk factor for adult schizophrenia.