Persistence of vaccine-induced antibody to measles 26-33 years after vaccination.

Because measles-specific antibody titer after vaccination is lower than after natural infection, there is concern that vaccinated persons may gradually lose protection from measles. To examine the persistence of vaccine-induced antibody, participants of a vaccine study in 1971, with documentation of antibody 1-7 years after vaccination, were followed up in 1997-1999 to determine the presence and titer of measles antibody. Of the 56 participants (77% were 2-dose recipients), all had antibodies detected by the plaque reduction neutralization (PRN) antibody assay an average of 26-33 years after the first or second dose of measles vaccine; 92% had a PRN titer considered protective (>1 : 120). Baseline hemagglutination inhibition antibody titer in 1971 strongly predicted follow-up PRN antibody titer (P<.001). Persistence of antibody in these primarily 2-dose recipients supports the current elimination strategy to achieve and sustain high population immunity with a 2-dose schedule.