Vaccinations for such childhood diseases as measles, mumps, and rubella (MMR) have significantly reduced the serious complications of these infections. However, public concern has become focused on the possible side effects of these immunizations. Mäkelä and colleagues conducted a retrospective investigation of data to determine whether there is any association between MMR vaccine and neurologic sequelae, such as encephalitis, aseptic meningitis, or autism.

Vaccination records from a register of 535,544 one- to seven-year-old children from November 1982 to June 1986 in Finland were reviewed. All patients from the review who were vaccinated within three months of hospitalization for encephalitis or aseptic meningitis were identified, and the number of episodes was compared with expected rates. A similar method was used in determining the relationship between vaccination and the first hospitalization for autism; however, there was no defined risk period for autism. Records also were reviewed for hospital visits for inflammatory bowel disease.

Among the children who received vaccinations, there were 199 hospitalizations for encephalitis, 161 for aseptic meningitis, and 352 for autism. There was no significant excess in the number of hospitalizations for meningitis or encephalitis during the study period. In fact, the overall incidence of these illnesses decreased during that time period. No distinguishable cluster of events occurred among children hospitalized for autistic disorders. None of the visits for autism involved a diagnosis of inflammatory bowel disorder.

The authors concluded that there was no association between MMR vaccine and neurologic disorders. The decrease in encephalitis and meningitis cases over the study period supports the protective effect of the MMR vaccine against these illnesses as sequelae of measles, mumps, and rubella. However, the authors acknowledge that certain strains of the mumps vaccine (especially the Urabe strain used in Russia, Japan, and Brazil) have been shown to cause encephalitis and aseptic meningitis. No strain association has been found between the MMR vaccine and autism or inflammatory bowel disease.