Mumps caused by an inadequately attenuated measles, mumps and rubella vaccine

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Abstract
PROBLEM:Reports of mumps following measles, mumps and rubella (MMR) immunization.OBJECTIVE:To determine whether mumps was caused by immunization or whether there was a concurrent epidemic of a wild strain of mumps.DESIGN AND PARTICIPANTS:Analysis of surveillance data and a cohort study of three schools that participated in the campaign.OUTCOME MEASURES:Cases of clinical mumps and orchitis, and immunization history and records were reviewed. The MMR vaccine was produced by the Serum Institute of India and contained the Leningrad-Zagreb strain of mumps virus. Four lots were used in the specific immunization campaign.RESULTS:Sentinel health facility surveillance showed an increase in mumps after two school immunization campaigns in western Suriname and a mass immunization campaign in the same region. There was also an increase in a geographically separate region following a mass campaign with the same vaccine. Three hundred fifteen children from three schools that were targeted in the immunization campaign were interviewed. The attack rate for mumps in those immunized was 15.1%; in those not immunized, the attack rate was 4.7%. In the affected males, the attack rate for orchitis was five of 19 (21%). Assuming 90% protection by the MMR vaccine, the incidence ratio (observed to expected) was 32.CONCLUSIONS:The mumps outbreak was caused by an inadequately attenuated MMR vaccine. Because this vaccine had not been used in these populations before in Suriname, it was not possible to determine wether the outbreak was due the virulence of the Leningrad-Zagreb mumps strain or due to production problems with one or more specific lots of vaccine. The vaccine was withdrawn from further use.