Rubella-specific serum and nasopharyngeal antibodies in volunteers with naturally acquired and vaccine-induced immunity after intranasal challenge.

Thirty-nine volunteers, who were either naturally immune to rubella virus or immune as a result of vaccination with RA 27/3, Cendehill, or To-336 vaccines, were challenged intranasally with high-titered RA 27/3 virus. Before and after challenge, rubella-specific IgG and IgA in serum and nasopharyngeal washings were measured by hemagglutination inhibition, neutralization, and radioimmunoassay. The reinfection rate (at least a fourfold rise in titer of serum antibody by one or more tests) was highest among recipients of Cendehill vaccine. Significant rises in titer were most frequently detected by radioimmunoassay for rubella-specific IgG. After challenge of immune volunteers, rubella-specific IgM was detected in six of the 29 with vaccine-induced immunity. Although high levels of rubella-specific serum and nasopharyngeal IgA before challenge appeared to be associated with protection in recipients of RA 27/3 vaccine, no level of any antibody tested was invariably associated with protection. For comparison, volunteers with vaccine-induced immunity challenged intranasally with the same dose of vaccine after inactivation did not show evidence of reinfection.