Rubella Antibody Prevalence Among Women of Reproductive Age in Croatia: Implications for the Prevention of Congenital Rubella Syndrome

Background/Objectives: Rubella immunity in childbearing-aged women is crucial due to the risk of congenital rubella syndrome (CRS). This study analyzed temporal trends in rubella virus (RUBV) seroprevalence among women of reproductive age in Croatia. Methods: The study included 1490 childbearing-aged and pregnant women aged 16–45 years tested between January 2015 and December 2024. RUBV IgM and IgG antibodies were detected using a commercial ELISA, with IgM-positive samples further assessed for IgG avidity. Results: RUBV IgG antibodies were detected in 1407/1490 (94.4%) of participants, with significant differences between years ranging from 87.4% (2019) to 96.4% (2023). High seropositivity was observed across all age groups, with no significant differences (93.1–95.1%). The area of residence was not associated with seroprevalence (continental Croatia: 94.8%, coastal Croatia: 93.8%). Similarly, no significant differences in seropositivity were observed according to settlement type (urban regions: 94.1%, suburban/rural regions: 95.1%). The year of sampling was the only predictor that showed significance in the multivariate regression model. A statistically significant effect of calendar year was demonstrated, indicating that the odds of IgG seropositivity increased by approximately 8% per year. Conclusions: This study demonstrated consistently high RUBV seroprevalence among Croatian women of reproductive age across all age groups during the past decade. Maintaining this high level of immunity is crucial for the prevention of CRS.