Rubella: Reinfection of Vaccinated and Naturally Immune Persons Exposed in an Epidemic

The protective efficacy of vaccine-induced and naturally acquired immunity was compared in a prospective study of a rubella epidemic among military recruits. The population consisted of 190 men in the following categories with respect to immunity to rubella: 26 who were susceptible, 15 vaccinees who had been immunized two to three months previously and 149 who were naturally immune. As a result of the epidemic all 26 susceptible men were infected; rubella virus was recovered from the throats of 11. On the basis of hemagglutination-inhibiting and complement-fixing antibody responses, 80 per cent of those vaccinated and 3.4 per cent of those who were naturally immune were reinfected. Virus was recovered from the throat of one vaccinee, but from none of the reinfected naturally immune men. If precipitin antibody results are included, 100 per cent of vaccinees responded serologically. None of those reinfected became ill; among the susceptible men the ratio of inapparent to apparent infections was approximately 2:1.