Detection of Serum Antibodies against Measles, Mumps and Rubella after Primary Measles, Mumps and Rubella (MMR) Vaccination in Children

Background: In Iran, the measles, mumps and rubella vaccine (MMR) is administered in a two-dose protocol where the first dose is scheduled at 12 months of age. This study aims to determine the efficacy of the MMR vaccine by testing IgM and IgG antibody levels 4 - 7 weeks after primary vaccination. Methods: A single group cohort study was performed on healthy children, 12 - 15 months of age, who were vaccinated at health centers affiliated with Shahid Beheshti University of Medical Sciences in Tehran, from January to April 2009. Children with negative vaccination and/or clinical history for measles, mumps or rubella were administered the first dose of the MMR live attenuated vaccine. IgG and IgM antibodies were checked by enzyme linked immunoassay (ELISA) in serum samples 4 - 7 weeks after vaccination. A child was considered seropositive if antibody levels were higher than the assay cut-off level set by the ELISA kit. Results: Samples from 240 children were checked for antibodies against measles and rubella. Measles serum IgM level was positive in 71.7% of samples and IgG in 75.8%. The rubella serum IgM level was positive in 71.7% of children and IgG in 73.8%. From 190 blood samples that were checked for mumps antibodies, serum IgM was positive in 68.9% and IgG in 95.3%. No significant relationship was found between seropositivity and age or gender. Conclusion: IgG and IgM antibody levels were below the assay cut-off levels against measles and rubella in approximately one-fourth of the children following primary MMR vaccination. A second dose was necessary to raise the level of protection against measles and rubella.