Susceptibility to rubella and borderline immunity

Immunity to rubella in women of childbearing age has been determined by hemagglutination inhibition (HI) and/or hemolysis in gel (HIG) methods. Susceptibility was defined as absence of antibody at a dilution of 1:16 in HI and a hemolysis zone of less than 7 mm in HIG tests. In screening 30,330 women during the years 1980-81, 13.7% were found seronegative. Among 439 women immunized with RA-27/3 vaccine, 92% showed seroconversion, when tested by HI greater than or equal to 2 months following vaccination. Paired sera from 35 vaccines who remained seronegative were tested by two additional methods: sensitizing antibody (SA) and enzyme-linked immunosorbent assay (ELISA). Ten women were confirmed as vaccine failures by these two methods. The remaining women presented the following results: 19 had borderline and stable titers in their paired sera and 6 showed seroconversion, by SA and ELISA. These results indicate that both SA and ELISA are more sensitive than the HI and HIG tests for evaluation of rubella immunity and response to vaccination.