Determination of rubella virus-specific humoral and cell-mediated immunity in pregnant women with negative or equivocal rubella-specific IgG in routine screening

Background: Immunity to rubella-virus (RV) is commonly determined by measuring specific IgG (RV-IgG). However, RV-IgG results may be different and even discordant, depending on the assay used. Cell-mediated immunity is not routinely investigated for diagnostic purposes.

Objectives: Our aim was to investigate humoral and cellular immunity of women with negative or equivocal RV-IgG before, and after post-partum vaccination.

Study design: A total of 186 pregnant women were included in the study. During pregnancy, humoral immunity was investigated with two RV-IgG immunoassays, an immunoblot and a T-cell mediated immunity test. In the post-partum vaccination period, measuring RV-IgM and RV-IgG avidity allowed us to determine whether women raised a primary or a secondary immune response.

Results: Before vaccination, 52.2% women, supposed to be susceptible, had positive anti-E1 RV-IgG indicating strong evidence of previous exposure to RV. All (100%) pregant women who had a positive immunoblot before immunization raised a secondary immune response to vaccination, and 96.8% who had a negative immunoblot before immunization, raised a primary immune response to vaccination. All women who raised a primary immune response after vaccination had negative anti-E1 RV-IgG and negative cell-mediated immunity.

Discussion: These results indicate that individuals can have evidence of protective immunity against rubella despite negative RV-IgG.