MMR2 IMMUNIZATION AT 4 TO 5 YEARS AND 10 TO 12 YEARS OF AGE - A COMPARISON OF ADVERSE CLINICAL EVENTS AFTER IMMUNIZATION IN THE VACCINE SAFETY DATALINK PROJECT

Background. The Advisory Committee on Immunization Practices recommend s a second dose of measles, mumps, and rubella vaccine (MMR2) at age 4 to 5 years of age, whereas the American Academy of Pediatrics suggest s MMR2 immunization at age 11 to 12 years of age. Because there is lit tle information on whether the rate of adverse reactions to MMR2 immun ization varies among these two age groups, we took advantage of differ ing immunization policies at two large HMOs to compare the frequency o f clinical events after, and possibly related to, MMR2 immunization. M ethods. information was collected on clinical events plausibly associa ted to MMR immunization (seizures, pyrexia, malaise/fatigue, nervous/m usculoskeletal symptoms, rash, edema, induration/ecchymoses, lymphaden opathy, thrombocytopenia, aseptic meningitis, and joint pain) in two c ohorts. At three facilities at Northern California Raiser (Oakland, CA ), 8514 children received MMR2 immunization at age 4 to 6 years of age ; at Group Health Cooperative (Seattle, WA) 18036 children received MM R2 immunization at age 10 to 12 years of age. To account for age-relat ed differences in health care use, within each HMO, clinical events in a 30-day period after immunization were compared with a 30-day period before vaccination. Results. Children 10 to 12 years of age were 50% more likely to have a clinical event after MMR2 immunization than in t he period before immunization (odds ratio, 1.45; 95% confidence interv al: 1.00,2.10). Children 4 to 6 years of age were less likely to have a visit for an event after immunization compared with the period befor e immunization (odds ratio, 0.64; 95% confidence interval: 0.40,1.01). Conclusions. These results suggest that the risk for clinical events after MMR2 immunizations is greater in the 10- to 12-year age group.