Waning antibody levels and avidity: implications for MMR vaccine-induced protection.

BACKGROUND The measles-mumps-rubella (MMR) vaccine is effective in eliciting a good antibody response. In addition to the amount of antibodies, the avidity of these antibodies might be important in protecting against disease. METHODS The amount of circulating antibodies for measles, mumps, and rubella was measured with enzyme immunoassays, and the avidity of these antibodies was determined by urea dissociation. Three groups of twice-MMR-vaccinated individuals and 1 group of naturally infected individuals were studied. One vaccinated group (n = 71) was studied 6 months and 20 years after a second MMR vaccination. RESULTS The antibody avidity indexes were high for measles and rubella but low for mumps. Twenty years after a second MMR vaccination, antibody levels for all 3 viruses waned. Also, the mean avidity index decreased by 8% for measles, 24% for mumps, and remained unchanged for rubella. Antibody avidity correlated with antibody concentration for measles. There was partial correlation for rubella and no correlation for mumps. CONCLUSIONS Measles and rubella induced high-avidity antibodies and mumps induced low-avidity antibodies after both vaccination and natural infection. Waning of both the concentration as well as the avidity of antibodies might contribute to measles and mumps infections in twice-MMR-vaccinated individuals.