Persistence of immunity against measles in persons immunized with Edmonston-Zagreb vaccine.

Cohorts of 30 children--470 in all--vaccinated against measles 2 to 17 years earlier were tested for measles heminhibiting antibodies. The vaccinees were randomly selected from a semi-urban, semi-rural population where the circulation of the wild measles virus has never been interrupted. The vaccinal status of the vaccinees varied widely, some were vaccinated only once, some twice or even three times, in some the primary vaccination was performed with a measles monovalent and in some with a combined MMR vaccine, only the revaccination having always been performed with a monovalent vaccine. The results of this serologic study reveal that the vaccine-induced immunity against measles does not fade with time, on the contrary, as judged by the mean geometric antibody titers, it rises. This is speculatively attributed to the booster effect of natural reinfection(s). Thereafter it is demonstrated that revaccination(s) do not yield a better immunity than the primary vaccination alone. This "revaccination", if withheld, helps only to attain a better coverage of children that have escaped primary vaccination.