Burden of congenital rubella syndrome (CRS) in India based on data from cross-sectional serosurveys, 2017 and 2019–20.

Background: India has set a goal to eliminate measles and rubella/Congenital Rubella Syndrome (CRS) by 2023. Towards this goal, India conducted nationwide supplementary immunization activity (SIA) with measles-rubella containing vaccine (MRCV) targeting children aged between 9 months to <15 years and established a hospital-based sentinel surveillance for CRS. Reliable data about incidence of CRS is necessary to monitor progress towards the elimination goal. Methods: We conducted serosurveys in 2019–20 among pregnant women attending antenatal clinics of 6 hospitals, which were also sentinel sites for CRS surveillance, to estimate the prevalence of IgG antibodies against rubella. We systematically sampled 1800 women attending antenatal clinics and tested their sera for IgG antibodies against rubella. We used rubella seroprevalence data from the current survey and the survey conducted in 2017 among antenatal women from another 6 CRS surveillance sites to construct a catalytic models to estimate the incidence and burden of CRS. Result: The seroprevalence of rubella antibodies was 82.3% (95% CI: 80.4–84.0). Rubella seropositivity did not differ by age group and educational status. Based on the constant and age-dependent force of infection models, we estimated that the annual incidence of CRS in India was 225.58 per 100,000 live births (95% CI: 217.49–232.41) and 65.47 per 100,000 live births (95% CI: 41.60–104.16) respectively. This translated to an estimated 14,520 (95% CI: 9,225–23,100) and 50,028 (95% CI: 48,234–51,543) infants with CRS every year based on age-dependent and constant force of infection models respectively. Conclusions: Our findings indicated that about one fifth of women in the reproductive age group in India were susceptible for rubella. The estimates of CRS incidence will serve as a baseline to monitor the impact of MRCV SIAs, as well progress towards the elimination goal of rubella/CRS. Author summary: Rubella infection during the first trimester of pregnancy can affect fetus, resulting in spontaneous abortion, stillbirth or birth of a baby with a combination of birth defects known as congenital rubella syndrome (CRS). Vaccination with rubella containing vaccine (RCV) is recommended as one of the strategies for eliminating rubella/CRS. The Southeast Asia region has set a target to eliminate rubella/CRS by 2023. Towards this goal, India completed nationwide immunization campaigns using measles-rubella vaccine during 2017–19, targeting children aged 9 months to <15 years. A case-based surveillance for CRS was initiated in five sentinel hospitals (Phase-1) in 2016 and later expanded to additional 6 sites (Phase-2) in 2019, to estimate burden of CRS and monitor its trend. As an adjunct to CRS surveillance, periodic serologic surveys were also planned to monitor the rubella seroprevalence among the pregnant women. A serosurvey conducted in 2017 indicated that 83.4% pregnant women attending antenatal clinics of Phase-1 sentinel hospitals had IgG antibodies against rubella. The second serosurvey conducted during 2019–20 in 6 Phase-2 sites indicated a comparable seroprevalence of 82.3%. Using seroprevalence data from these two serosurveys, we estimated that the annual incidence of CRS in India was 225.58 per 100,000 live births with constant force of infection and 65.47 per 100,000 live births with age-dependent force of infection model. This incidence rates translated to an estimated 14,520 to 50,028 infants with CRS every year. The estimates of CRS incidence will serve as a baseline to monitor the progress towards the elimination goal of rubella/CRS in India. [ABSTRACT FROM AUTHOR]