A large observational study to concurrently assess persistence of measles specific B-cell and T-cell immunity in individuals following two doses of MMR vaccine.

The measurement of measles-specific neutralizing antibodies, directed against the surface measles virus hemagglutinin and fusion proteins, is considered the gold standard in measles serology. We assessed functional measles-specific neutralizing antibody levels in a racially diverse cohort of 763 young healthy adolescents after receipt of two doses of measles-mumps-rubella vaccine, by the use of an automated plaque reduction microneutralization (PRMN) assay, and evaluated their relevance to protective antibody levels, as well as their associations with demographic and clinical variables. We also concurrently assessed measles-specific IFNγ Elispot responses and their relation to the observed antibody concentrations. The geometric mean titer for our cohort was 832mIU/mL (95% CIs: 776; 891). Sixty-eight subjects (8.9%) had antibody concentrations of less than the protective threshold of 210mIU/mL (corresponding to PRMN titer of 120; suggesting protection against symptomatic disease), and 177 subjects (23.2%) demonstrated persisting antibody concentrations above 1841mIU/mL (corresponding to PRMN titer of 1052; suggesting total protection against viral infection), 7.4 years after vaccination, in the absence of wild-type virus boosting. The mean measles-specific IFNγ Elispot response for our cohort was 46 (95% CIs: 43; 49) IFNγ-positive spots per 200,000 cells with no relation of cellular immunity measures to the observed antibody concentrations. No significant associations between antibody titers and demographic and clinical variables, including gender and race, were observed in our study. In conclusion, in a large observational study of measles immunity, we used an automated high-throughput measles virus-specific neutralization assay to measure humoral immunity, and concurrently determined measles-specific cellular immunity to aid the assessment of potential susceptibility to measles in vaccinated populations.