Measles immunization strategy: measles antibody response following MMR II vaccination of children at one year of age.

Measles antibody levels were determined by the plaque reduction neutralization (PRN) test in 580 one-year-old children before vaccination and four to six weeks after MMR II vaccination. Fifty-one (8.8%) had maternally derived measles antibody at prevaccination, and this was more common among children of women born before 1967 (10.6%) vs. 4.3%; p < 0.01). Among those with maternal antibody, only 22 (43.1%) responded with a protective PRN titre of over 120, in contrast to 463 (87.5%) of the 529 without maternal antibody at prevaccination (p < 0.0001). Also, the geometric mean titre was significantly lower for the former (114.1 vs. 378.5; p < 0.0001). Overall, 15 (2.6%) of the 580 children had no antibody response after vaccination, and a further 80 (13.8%) had a subprotective response (PRN titre < 120). This lack of response could not be attributed entirely to the presence of maternal measles antibody at the time of vaccination. The MMR II vaccine may not be sufficiently immunogenic in inducing adequate measles antibody response after a single dose given at one year of age.