Persistence of vaccine-induced immune responses to rubella: comparison with natural infection.

Serologic responses and patterns of antibody persistence in children given HPV-77 DE-5 or RA27/3 vaccine were compared with those in children who had experienced natural infection. The results indicated that both vaccines induce long-lasting immunity in most individuals. RA27/3 vaccine proved more immunogenic and resulted in higher antibody titers; after 11 years 95% of those who seroconverted who were tested had hemagglutination-inhibiting (HAI) antibodies and 100% had neutralizing (NT) antibodies. Titers in HPV-77 DE-5 vaccinees were lower, and in 16% of those whose immune responses were feeble, HAI titers decreased to less than 1:8 after nine to 12 years; however, when their sera were examined by the more sensitive latex-agglutination test, all but two were found to have specific rubella antibody at levels of 1:1 to 1:16. Natural infection with wild virus was shown to induce more vigorous immune responses than did either vaccine: antibody titers were higher, decreases were smaller, and none fell to less than 1:8 (HAI) or less than 1:4 (NT).

Durability of antibody titers induced by RA27/3 rubella virus vaccine.

The RA27/3 rubella virus vaccine induced titers of hemagglutination-inhibiting antibody that were slightly lower than those induced naturally, but after an initial decline the titers remained stable even in the absence of reexposure to rubella virus.

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.