uMMARY A rubella epidemic occurred in an institutional population composed of 189 susceptible, 37 naturally immune, 35 previously vaccinated and 38 serologically Lincharacterized children and nursing staff. The epidemiclasted 3.5 months and showed more than 5 waves. Detailed clinical and serological examinations of these subjects \\. ere made. A raslT appeared in 156 (521",) of 299 persons, in duding 145 (87%) of 166 unvaccinated and setologically uricharacterized subjects, but not in the 72

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... une persons In the middle of the 3rd \\, ave urgent \, accination of 61 children aged O to 2 years of the susceptible group reduced the rate of appearance of a rash to 11 of the children (18%), as compared \\, ith 126 (98%) of 128 subjects in the unvaccinated non-immune group. The epidemic only reached a 4th wave in the \, accinated group, but it extended to a 5th \\, ave or more in unvaccinated subjects. None of the 35 subjects in a previously vaccinated group developed rubella, although the rate of subclinical reinfection in this previously vaccinated group was higher (35%) than that in the naturally immune group (1796). Three cases of subclinical reinfection were detected even among 6 previously ^evaccinated subjects.