Meningitis after MMR vaccination in Mashhad, Iran

Background: More than 20 years after the introduction of the mumps vaccine in the Iranian national vaccination program, there are concerns about meningitis induced by the Measles, Mumps, and Rubella (MMR) vaccine. The aim of this study is to virologically determine the incidence of MMR-induced meningitis in Mashhad, Iran. Method: This is an observational prospective study during which all children who were admitted (in all hospitals of Mashhad) under the clinical suspicion of meningitis and had a history of MMR vaccination during the past 45 days were included. A polymerase chain reaction (PCR) test for mumps virus and enterovirus (EV) was done on cerebrospinal fluid (CSF) samples with pleocytosis. Results: During 13 months of study, 55 children were hospitalized for suspicion of meningitis and had a history of recent MMR shots (94% presented with a febrile seizure). Meningitis was confirmed by CSF pleocytosis in 23 (2 bacterial and 21 aseptic) cases (44.2%). All incidents of meningitis had occurred after the first MMR. The incidence of any kind of aseptic meningitis, EV meningitis, and mumps meningitis during 45 days after the first MMR was, respectively, 19.9, 5.71, and 1.9 per 100,000 cases. The number of meningitis cases during the first 3 months after MMR was, respectively, 4.5 and 2 times more than the cases that occurred during the 3 months before and 3-6 months after MMR. Conclusion: Around 40% of all cases of meningitis (between 4 and 43 months of age) occur during the first 3 months after the first MMR vaccination (12-15 months). The disproportionate increase of aseptic meningitis after the first MMR is strong epidemiologic evidence in favor of mumps vaccine induced meningitis.