SERUM LEVELS OF RUBELLA-VIRUS ANTIBODIES INDICATING IMMUNITY - RESPONSE TO VACCINATION OF SUBJECTS WITH LOW OR UNDETECTABLE ANTIBODY CONCENTRATIONS

To define the concentration of anti-rubella virus (RV) antibodies disc riminating nonimmune from immune persons and to characterize immune re sponses to rubella vaccination, serologic studies were performed after rubella vaccination in persons with low or undetectable antibody conc entrations, Thirty-six subjects with primary immune responses had prev accination anti-RV IgG concentrations <15 IU/mL by ELISA and negative results by radial hemolysis. Eighty-three subjects with secondary immu ne responses had mean IgG increases of 9 IU/mL within 2 weeks. Eight o f them had initial IgG levels <15 IU/mL, and 2 were negative by radial hemolysis, Both groups attained similar antibody levels after 1-3 mon ths. Secondary immune responses to rubella vaccination were delayed by >2 weeks and thus resembled the time course of primary immunization, but IgM responses and IgG avidity were distinct between subjects with primary or secondary immune responses, Thresholds for immunity <15 IU/ mL entail the risk of withholding rubella vaccination from susceptible persons.