Clinical efficacy of rubella vaccine.

In the period October 10, 1980, to January 19, 1981, 83 cases of rash illness compatible with rubella were reported in Sanford, ME. Twenty-two (27%) were confirmed serologically. Forty cases (48%) occurred in Sanford High School students; the overall attack rate was 3.2%. A case-control study was undertaken to determine the effectiveness of rubella vaccine in preventing clinical rubella. Bayes' theorem was used to calculate the attack rates in the vaccinated population (ARV) and the unvaccinated population (ARU). Vaccine efficacy (VE), calculated with use of the formula VE (%) = [(ARU - ARV)/ARU] x 100, was 90%. These results indicate that rubella vaccine is highly effective in preventing clinical rubella and do not support proposals for routine revaccination.