Rubella antibody titres and immunization status in a family practice.

Rubella vaccination status and immunity to rubella were studied in 230 "active patients" aged 8 to 22 years in a teaching family practice by means of a chart review and measurement of the rubella antibody titre in a blood sample. Of the 200 patients who submitted a blood sample 161 (80%) were found to be immune, having a rubella hemagglutination-inhibiting antibody titre of 1:16 or greater. Log linear analysis showed that immunity to rubella was independent of a history of rubella, and that 94% of the vaccinated patients versus 74% of the unvaccinated patients (a significant difference; P = 0.007) were immune. In retrospect we estimated that 80% of the study group were protected at the start of the study. After surveillance and follow-up, with vaccination of 27 of the 39 patients identified as susceptible to rubella, this estimated proportion increased to 90%. The study showed that there is nothing to be gained by asking about a history of rubella but that vaccination against this disease is increasing among children aged 5 to 9 years.