Twenty-three-year follow-up study of rubella antibodies after immunization in a closed population, and serological response to revaccination.

Twenty-six institutionalized children immunized with a Japanese rubella vaccine, Matsuba strain, have been observed for 23 years and the persistence of vaccine-induced rubella immunity documented. All vaccinees were shown to have seroconverted to rubella virus in a haemagglutination inhibition (HI) test, and the geometric mean titre (GMT) of rubella HI antibody rose to 2 5-8 months after vaccination (Ueda et al., Acta Paediatrica Japonica, Overseas Edition 1978, 20, 8-14). The GMT then declined gradually to 2 23 years after inoculation, except in four cases (15.4%) which had reverted to negative. However, three of the four maintained a rubella HI antibody titre of 1:4. Twelve of the 26 vaccinees were revaccinated 24 years after primary vaccination, and all ten cases having initial titres of < or = 1:16 demonstrated secondary responses. Rubella immunity induced by vaccination had persisted, so routine booster immunization did not seem necessary. However, a second immunization programme should be considered to achieve high antibody-positive rates and to protect against primary vaccine failure.