DECLINE OF MEASLES-SPECIFIC IMMUNOGLOBULIN-M ANTIBODIES AFTER PRIMARYMEASLES, MUMPS, AND RUBELLA VACCINATION

Detection of measles-specific immunoglobulin M (IgM) has become the st andard diagnostic method for laboratory confirmation of measles, In ou tbreaks, the interpretation of an IgM-positive result can be complicat ed when persons with suspected measles receive a dose of measles vacci ne as part of outbreak control measures. This investigation evaluated the decay of measles-specific IgM antibodies 1 to 4 months after prima ry vaccination with measles, mumps, and rubella vaccine (MMRII). Serum samples were obtained from 536 infants vaccinated when they were 15 m onths old as part of a study to assess primary and secondary measles v accine failure, Sixty serum specimens per week were selected from spec imens collected between 4 and 9 weeks after MMRII vaccination; all 176 available serum specimens collected between 10 and greater than or eq ual to 16 weeks were included, Specimens were tested for the presence of measles-specific IgM by an antibody-capture enzyme immunoassay. The proportion of IgM-positive specimens dropped from 73% at 4 weeks afte r vaccination to 52% at 5 weeks after vaccination and then declined to 7% by 8 weeks after vaccination. Less than 10% of children remained I gM positive between 9 and 11 weeks, An IgM-negative result helps rule out the diagnosis of measles in a person with suspected infection and a history of recent vaccination, The interpretation of a positive IgM result from a person with a clinically suspected case of measles and a recent history of measles vaccination (especially within 8 weeks) is problematic, and the diagnosis of measles should be based on epidemiol ogic linkage to a confirmed case or on detection of wild-type measles virus.