Measles-specific lymphocyte reactivity and serum antibody in subjects with different measles histories.

Measles hemagglutination-inhibiting (HAI) antibody titers and measles-specific lymphocyte reactivity were studied in subjects who had previously received killed measles vaccine and had been recently reimmunized with live vaccine--persons who previously had atypical measles, subjects with multiple immunizations with live vaccine, adults with a history of measles, and persons with primary measles immunization. Twelve to 18 months after revaccination of former recipients of killed vaccine, all 31 subjects had measles HAI antibody titers greater than or equal to 10 and only three had lymphocyte stimulation indices (LSI) greater than 2.8. The mean LSI and geometric mean titer of antibody were similar to those of persons who had had natural measles many years ago. One subject who previously had atypical measles had an HAI titer of less than 5 and an LSI of 0.5; another had an LSI of 6.0 and an HAI titer of 80. Only one of seven subjects who were immunized more than once with live vaccine had an LSI of greater than 2.8 one year later. The finding of measles-specific lymphocyte reactivity and antibody levels in revaccinated former recipients of killed vaccine that are similar to those in persons who had natural measles suggests that the risk of future atypical measles in this group is slight.