The ground work for this research thesis was completed seven years ago when the Dow Pharmaceutical Company selected Muncie, Indiana to test their new rubella vaccine. In the Fall of 1970, 311 seronegative elementary school children were innoculated with HPV-77, DK12 rubella vaccine. Of the 302 children who seroconverted, 98 were available for follow-up six years post innoculation. The participant's sera drawn six years previously was recovered in order to determine a six week and six year post innoculation titer on paired specimens. All 98 children, when retested, has measurable antibody. The geometric mean titer six years post innoculation was 55; a 14% decrease from the geometric titer of 64 six weeks after innoculation. At the six year point in time, there was at least a 9.2% incidence of subclinical reinfection, detected by a fourfold rise in the HI-titer, within the study group.Ball State UniversityMuncie, IN 47306