Researchers discovered that the rate of autism, which has been increasing in recent years, continued to increase among the children in the study group even after the MMR vaccine was withdrawn from use.

Dr. Hideo Honda of the Yokohama Rehabilitation Center and colleagues Dr. Yasuo Shimizu and Dr. Michael Rutter of the Institute of Psychiatry in London, who conducted the study of children in the city of Yokohama, reported their findings in the Journal of Child Psychology and Psychiatry.

Earlier Study Evoked Dramatic Response

An earlier study, led by Dr. Andrew Wakefield and published in The Lancet in 1998, sparked widespread concern that the MMR vaccine might trigger autism. Dr. Wakefield's research involved 12 children from 3 to 10 years of age, including 11 boys, who were referred to a pediatric gastroenterology unit with a history of normal development followed by loss of acquired skills, including language, together with diarrhea and abdominal pain.

Dr. Wakefield reported that parents of 8 of the 12 children associated the onset of behavioral symptoms with the MMR vaccine. Nine cases of autism were identified among the 12 children, and Dr. Wakefield theorized -- based on his observations together with the results of earlier studies -- that a real connection existed between the MMR vaccine and onset of autism.

The 1998 study created a stir in the UK, with parents abandoning the MMR vaccine and opting for single vaccines instead. Measles outbreaks occurred, fueling fear of an epidemic.

Autism Increased Without Vaccine

The new study led by Dr. Honda reportedly shows that occurrences of autism continued to rise among children in the city of Yokohama after the MMR vaccine was replaced with single vaccines. Japan had discontinued use of the triple vaccine in 1993 due to reports that the mumps component was causing meningitis.

Dr. Honda's work is said to be the first investigation of a possible MMR link to autism in an environment where the MMR vaccine was not being used. Together with colleagues Dr. Shimizu and Dr. Rutter, Dr. Honda examined records of 31,426 children born in a single Yokohama district between 1988 and 1996.

The team discovered that the rate of autism, which has been increasing in recent years, continued to increase among the children in the study group even after the MMR vaccine was withdrawn from use. This observation was true for autism generally and also for the specific type of autism that Dr. Wakefield had observed in his study, which was characterized by normal development followed by sudden regression.

Rising Autism Rate a Mystery

Researchers in the Japanese study reportedly acknowledged that MMR might trigger autism in a very small number of children. Although they found no evidence to support that hypothesis, they were unable to rule it out.

Still, if such a finding were established, it would not explain the rising rate of autism in Japan following the discontinuation of the vaccine's use.

Experts agree that further study is needed to explain the worrisome rise in autism cases.