Historically, the adoption for general use of each new vaccine has brought to light a variety of problems. Rubella vaccine, licensed last year for general distribution, has proved to be no exception. Certain potential difficulties were recognized early in its development but were considered to be of minor importance. Others emerged only when vaccination began to be practiced on a large scale. The adoption in this country of a novel hypothesis governing the application of this product has introduced a source of complications not inherent in the use of earlier attenuated virus vaccines.According to this hypothesis, prevention of infection . . .