During the investigation of a measles outbreak in a rural community, a spectrum of illness was observed which ranged in severity from a brief febrile illness to one characteristic of typical measles. Unimmunized children were more apt to develop measles (p < 0.001) than were immunized children. However, a proportion of both the immunized and unimmu-

The relationship between the development of measles and age at immunization and time since immunization is examined using a trichotomous logistic distribution with maximum likelihood estimation of the parameters. The first and second partial derivatives used in the estimation scheme are presented.