Immune response to second dose of MMR vaccine in Indian children.

Background & objectives: MMR vaccine in a two dose schedule has successfully eliminated measles, mumps and rubella from many developed countries. In India, it is not a part of national immunization programme but is included in the State immunization programme of Delhi as a single dose between 15-18 months. This prospective study was carried out to assess the extent of seroprotection against these three diseases in immunized children and to study the immune response to a second dose of MMR. Methods: Consecutive children aged 4-6 yr, attending the immunization clinic of a tertiary care hospital in Delhi for routine DT vaccination, were enrolled. Second dose of MMR was given and pre- and post-vaccination antibody levels were compared. Results: The pre-vaccination percentage seropositivity observed in the 103 children recruited, was 20.4 per cent for measles, 87.4 per cent for mumps and 75.7 per cent for rubella. Amongst the 84 children who were followed up after the second dose, the percentage seroprotection for measles rose from 21.4 (18/84) to 72.6 per cent (61/84) and 100 per cent became seroprotected to mumps and rubella. Interpretation & conclusions: The percentage of children protected against measles was found to be alarmingly low which needs to be investigated. Though the observed protection against mumps and rubella was adequate, its durability was not known. The need for re-appraisal of the current MMR immunization policy is called for by carrying out longitudinal studies on a larger sample.