A population-based case-control study on viral infections and vaccinations and subsequent multiple sclerosis risk.

Viral infections are probably involved in the pathogenesis of multiple sclerosis (MS). A recent cohort study in the Gothenburg population revealed no change in MS incidence associated with the introduction of the Swedish measles, mumps and rubella vaccination programmes. The aim of the present study was to clarify whether these infections or vaccinations, and two other infections, varicella and infectious mononucleosis, influence MS risk. We performed a population-based case-control study in Gothenburg that included 509 MS cases and 2,067 controls, born 1959-1986. Data on infections and vaccinations were obtained from questionnaires and from child health and school health records. We found no significant associations between measles, mumps, rubella or varicella and MS risk. These results were consistent between the two source materials. Infectious mononucleosis was associated with significantly higher MS risk (odds ratio 2.03, 95% CI 1.52-2.73). Overall, there was no significant association between measles-mumps-rubella (MMR) vaccination and MS risk, while those MMR vaccinated before age ten only were at significantly higher MS risk (odds ratio 4.92, 95% CI 1.97-12.20). Those MMR vaccinated both before and after age ten had intermediate MS risk. Infection with measles, mumps, rubella and varicella did not influence MS risk in contrast to infectious mononucleosis which conferred doubled MS risk. The association with 'early' MMR vaccination only was an isolated finding, limited by a small number of subjects and multiple testing. Most likely this was a chance finding. Future studies could investigate it on an a priori basis.