STUDIES by others have indicated that attenuated strain high passage virus-77 (HPV-77) or HPV-77 derived attenuated rubella vaccines are capable of inducing significant (fourfold or greater) increases in hemagglutination inhibiting (HI) and neutralizing antibody titers in at least 95% of susceptible children.1-3 Although this acquisition of antibody is often accompanied by pharyngeal shedding of the vaccine viruses, spread of these viruses to susceptible contacts has not been reported.1-3
To estimate the protective efficacy of HPV-77 induced antibodies, Meyer et al1 challenged five children by intranasal administration of pharyngeal secretions containing 100 tissue culture interfering dose50's (InD50) of rubella virus 8 to 12 months after the five had received HPV-77 vaccine. Although none of these five children with HPV-77 induced antibodies developed clinical rubella or shed rubella virus after challenge with "wild" virus, two had significant increases in HI, neutralizing, and complement fixing (CF) antibodies.1