Long-term Immunogenicity of Measles Vaccine: An Italian Retrospective Cohort Study.

Abstract

BackgroundLevels of antibodies induced by the measles virus–containing vaccine have been shown to decline over time, but there is no formal recommendation about testing immunized subjects (in particular, healthcare workers [HCWs]) to investigate the persistence of measles immunoglobulin G (IgG).MethodsThis study aims to evaluate the long-term immunogenicity of measles vaccine in a sample of medical students and residents of the University of Bari who attended the Hygiene Department for a biological risk assessment (April 2014–June 2018).ResultsTwo thousand immunized (2 doses of measles-mumps-rubella [MMR] vaccine) students and residents were tested; 305 of these (15%) did not show protective anti-measles IgG. This proportion was higher among subjects who received vaccination at ≤15 months (20%) than in those who received vaccination at 16–23 months (17%) and at ≥24 months (10%) (P < .0001). After an MMR vaccine booster dose, we noted a seroconversion of 74% of seronegative HCWs. The overall seroconversion rate after a second dose (booster) was 93%. No serious adverse events were noted after the booster doses.ConclusionsAn important proportion of subjects immunized for measles do not show a protective IgG titer in the 10 years after vaccination. Our management strategy seems consistent with the purpose of evidencing immunological memory.