Reactions to rubella vaccine and persistence of antibody in virgin-soil populations after vaccination and wild-virus-induced immunization.

Vaccination of two virgin-soil (without historical or serological evidence of past infection) populations of Amazon Indians with RA 27/3 rubella vaccine was followed by fever of greater than 100 F in 10% of the vacinees and by ephermeral arthralgia in 2%. These frequencies are not greater than those that have been reported for cosmopolitan populations of comparable ages. There was little or no secondary spread of the virus. Titers of hemagglutination-inhibiting antibody to rubella virus were prevalent in a third population of Amazon Indians, who had naturally acquired immunity and were unexposed to reinfection, and did not decline during a period of four to 12 years after infection. Antibody titers in the two virgin-soil populations immunized with RA 27/3 vaccine declined by twofold between four months and two and one-half years after vaccination but, at the end of that period, were not appreciably lower than antibody titers at four years in the naturally infected population. All age groups except children under one year of age responded to vaccination equally well.