Serious adverse events after measles-mumps-rubella vaccination during a fourteen-year prospective follow-up

Background, Several disorders have been attributed to measles-mumps-rubella (MMR) vaccination during the past decade. The aim of this prospective foll ow-up study was to identify serious adverse events causally related to MMR vaccination. Methods. When the MMR vaccination program was launched in Finland in 1982, a countrywide surveillance system was set up to detect serious adverse even ts associated with MMR. To obtain detailed case histories vaccinees' clinic al charts were reviewed. Serum samples were analyzed to trace concurrent in fections. Setting. All hospitals and health centers in Finland from 1982 through 1996 , Results. Immunization of 1.8 million individuals and consumption of almost 3 million vaccine doses by the end of 1996 gave rise to 173 potentially ser ious reactions claimed to have been caused by MMR vaccination. In all, 77 n eurologic, 73 allergic and 22 miscellaneous reactions and 1 death were repo rted, febrile seizure being the most common event. However, 45% of these ev ents proved to be probably caused or contributed by some other factor, givi ng an incidence of serious adverse events with possible or indeterminate ca usal relation with MMR vaccination of 5.3 per 100 000 vaccinees or 3.2 per 100 000 vaccine doses. Conclusions. Causality between immunization and a subsequent untoward event cannot be estimated solely on the basis of a temporal relation. Comprehens ive analysis of the reported adverse reactions established that serious eve nts causally related to MMR vaccine are rare and greatly outweighed by the risks of natural MMR diseases.