Rubella immunization. Persistence of antibody four years after a large-scale field trial.

A long-term comparative field trial of three live, attenuated rubella vaccines (HPV-77 DE-5, HPV-77 DK-12, and Cendehill) was initiated in 1969 on the islands of Kauai and Hawaii in the state of Hawaii. Rubella hemagglutination-inhibition (HI) tests on prevaccination serum specimens from 7,931 children in the two study areas indicated an overall susceptibility to rubella of nearly 70%. The rates of seroconversion of 5,153 seronegative subjects to HPV-77 DE-5, HPV-77 DK-12, and Cendehill vaccine were 97.5%, 99.9%, and 99.8%, respectively. Over the subsequent four-year follow-up period, during which time natural exposure to rubella was minimal, the percent decline of geometric mean titers did not vary substantially among the three vaccine groups and measured about twofold for all three. A total of only 28 vaccines (0.7%) who seroconverted to one of the vaccines in 1969 lost all measurable antibody by 1974. Measurable antibody persisted in more than 98% of all vaccinees over the four-year period. Reinfection, thought possibly to be an important factor in maintaining titers, did not occur frequently in the study population and could not be related to outbreaks of disease.