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.