Measles reimmunization in children seronegative after initial immunization

Objective.-To evaluate the success of measles reimmunization in children without measles antibody after the initial dose of measles vaccine. Design and Setting.-A prospective clinical trial in Olmsted County, Minnesota, and Northern Newfoundland and Labrador in Canada. Subjects.-A total of 130 healthy white, Innu, and Inuit schoolchildren. All subjects had received the post-1980 Moraten measles vaccine 4 to 11 years earlier. Methods.-Children previously identified as measles antibody seronegative or equivocal after 1 dose of measles vaccine were entered into the trial and reimmunized. Measles antibody was measured a minimum of 6 weeks later using a whole-virus IgG measles-specific enzyme-linked immunoassay (EIA). Results.-Of the 130 children reimmunized, 106 (81.5%) became measles antibody seropositive, but 24 children (18.5%) remained seronegative. Younger age at initial immunization (< 13 months vs ≤13 months) was significantly associated with lack of seropositive antibody levels following reimmunization (odds ratio, 3.9; 95% confidence interval, 1.5-9.7). In addition, antibody levels after reimmunization were significantly reduced with increasing time since initial immunization (P=.001). Conclusions.-After 2 doses of measles vaccine, 98.2% of all subjects in this study were seropositive for measles antibody, despite the fact that almost 20% of children did not have measurable antibodies 4 to 11 years following a first dose. These findings suggest that the current public health policy recommending a 2-dose measles immunization strategy, with the second dose given at school entry, will provide high levels of immunity in the community.