Decay of passively acquired maternal antibodies against measles, mumps, and rubella viruses

The decay of maternally derived antibodies to measles, mumps, and rubella v iruses in Swiss infants was studied in order to determine the optimal time for vaccination. A total of 500 serum or plasma samples from infants up to 2 years of age were tested by enzyme-linked immunosorbent assay and fluores cent-antibody testing. The decline of antibody prevalence was slowest again st the measles virus. By 9 to 12 months of age, only 5 of 58 (8.6%; 95% CI, 2.9 to 19.0) infants were antibody positive for the measles virus, and onl y 2 had levels above 200 mIU/ml, Mumps and rubella virus antibody seroposit ivity was lowest at 9 to 12 months of age with 3 of 58 (5.2%; 95% CI, 1.1 t o 14.4) infants and at 12 to 15 months with I of 48 (2.1%; 95% CI, 0.1 to 1 1.1) infants, respectively. Concentrations of passively acquired antibodies decreased rapidly within the first 6 months of life. We observed no signif icant differences in antibody prevalence or concentration according to gend er in any age group. In conclusion, MMR vaccination at 12 instead of 15 mon ths of age could reduce the pool of susceptible subjects in infancy and sup port the efforts to eliminate these infections, particularly in combination with a second vaccine dose before school entry.