Although many previous studies have linked prenatal exposure to influenza with adult schizophrenia, researchers say this is the first study based on laboratory evidence of flu exposure during pregnancy.
The study showed that the risk of schizophrenia was three times higher among adult children exposed to influenza during the first half of pregnancy compared with those who had not been exposed. But there was no increase in risk associated with influenza exposure during the second half of pregnancy.
"These findings represent the strongest evidence thus far that prenatal exposure to influenza plays a role in schizophrenia," says researcher Ezra Susser, MD, DrPH, chairman of the department of epidemiology at the Mailman School of Public Health at Columbia University, in a news release. "Although the findings may ultimately have implications for prevention, we strongly caution against making any public health policy recommendations until these links have been confirmed through further study."
Schizophrenia is a severe mental disorder that affects about 1% of the population. The exact cause is unknown, but it's likely caused by a combination of factors such as heredity, problems in the way the brain develops before birth, and problems experienced during pregnancy that may affect the development of the baby's nervous system, including exposure to a virus.
New Evidence of Influenza-Schizophrenia Link
In the study, which appears in the August issue of the Archives of General Psychiatry, researchers followed a large group of children born to mothers in Alameda County, Calif., who were part of the Child Health and Development Study from 1959-1966. The children were followed up for psychiatric disorders 30-38 years later.
Researchers identified 64 of the adult children as having schizophrenia and compared them to 125 similar, healthy study participants.
The study showed that the risk of developing schizophrenia was seven times higher among those children whose mothers were exposed to influenza during the first trimester of pregnancy based on blood tests.
There was no increased risk of schizophrenia associated with influenza exposure during the second or third trimester.
When researchers looked at a broader time period of influenza exposure during pregnancy, they found the risk of schizophrenia was about three times higher for those exposed during early to mid-pregnancy.
"Our data suggest the possibility that up to 14% of schizophrenia cases would not have occurred if influenza exposure during early to midpregnancy had been prevented," write the researchers.
Routine vaccination of nonpregnant women for the flu virus may be worth considering, the researchers write.