Booster vaccination with further live attenuated measles vaccine.

Revaccination with live attenuated measles vaccine was evaluated in a large group of children to determine (1) if protective antibody to measles infection could be augmented and (2) after what interval will the revaccination yield optimal results. The rate of decline in measles hemagglutination-inhibition (HI) antibody was observed to be directly related to the time interval since the previous vaccination, and individuals with declining titers became increasingly responsive to revaccination with a maximal response approximately four to six years after previous vaccination. Six-month follow-up studies demonstrated sustained elevations in measles HI antibody titers. Measles-neutralizing antibody showed less tendency to sustain a titer increase with revaccination. The observations suggest that revaccination with live, further attenuated measles vaccine is safe and may augment immunity.