Maternal rubella immunity gaps in the vaccine era: a seroepidemiological study of pregnant women in Jiangsu, China

Background Rubella elimination has substantially reduced virus circulation in China, but the changing pattern of immunity among women entering reproductive age remains unclear. We assessed the contemporary rubella immunity profile among pregnant women in Jiangsu Province. Methods We conducted a cross-sectional serological study of 1,196 pregnant women in Jiangsu Province. Rubella-specific IgG antibodies were quantitatively measured. Seropositivity and antibody concentrations were compared across maternal age and birth cohorts. Restricted cubic spline (RCS) regression was used to assess nonlinear associations between age and immunity, and multivariable regression identified factors associated with seronegativity. Results Overall rubella IgG seropositivity was 61.45%, with a geometric mean concentration of 24.21 IU/mL. Seropositivity increased from 37.77% among women aged ≤24 years to approximately 75% among women aged ≥30 years. Antibody concentrations showed a similar age-related gradient, with a nonlinear association between maternal age and rubella immunity. Younger birth cohorts consistently exhibited lower seropositivity and antibody concentrations, indicating a concentrated immunity gap among women entering reproductive age. Maternal age remained independently associated with rubella immunity, whereas gestational age was not. Conclusions Despite sustained high RCV coverage and declining rubella transmission in China, substantial heterogeneity in maternal rubella immunity persists. Younger women and more recent birth cohorts may represent important susceptibility groups. Integrating maternal immunity surveillance with sustained childhood vaccination and preconception prevention strategies may help maintain rubella elimination and prevent congenital rubella syndrome.