Correlation between Measles-neutralizing Antibody and HI Antibody, between Measles-neutralizing Antibody and PA Antibody Among Pregnant Women, and Protective Levels of Three Titration Types

When measles antibody levels among pregnant women were measured with measles hemagglutinin inhibition (HI), 31% of subjects had negative HI antibody titers. When the same blood samples were tested with measles gelatin particle agglutination (PA) and neutralizing (NT), the percentages of those with negative antibody levels were 1% and 3%. We conducted the correlation between antibody titers measured by the three types of titration. Correlation between NT and HI antibody titers higher than 1: 8 and that between NT and PA antibody titers were good, but 81 % of subjects whose HI antibody titer was below 1: 8 and all women with HI antibody of 1: 8 were found to have NT antibody titer higher than 1: 4. NT antibody titer higher than 1: 4 was found in 95% of women having PA antibody titer of 1: 256 and in 99% of those with PA antibody titer of 1: 512. Based on the relationships to measles NT antibody level, the majority of subjects with HI antibody titer higher than 1: 8 or PA antibody level higher than 1: 512 was reasonably assumed to be protected against clinical measles. PA seemed superior to HI in finding subjects with insufficient immunity against measles, because the former detects weak immunity more efficiently than the latter.