Population level immunity to measles and rubella 5 years before and after the MR campaign in urban Vellore, South India

India aims to eliminate measles and rubella (MR) by 2026. Despite >90% vaccination coverage reported in NFHS-5 and NFHS-6, assessing population-level immunity gaps remains essential to guide strategies for protecting vulnerable groups. We leveraged biobanked samples from two community-based serosurveys conducted in urban Vellore in 2013 and 2022, representing periods 5 years before and after the nationwide MR vaccination campaign. Age- and sex-stratified participants were tested for measles- and rubella-specific IgG antibodies using ELISA. Seroprevalence estimates were compared across surveys, and generalized additive models (GAM) were used to assess age-specific seropositivity patterns. Effective reproduction numbers (Re) for measles and rubella were estimated using mixture modeling approaches. A total of 1,029 samples from 2013 and 718 samples from 2022 were analyzed. Measles seroprevalence increased from 33%, 41%, 47%, and 48% in the 1-5, 6-15, 16-40, and >40 years age groups in 2013 to 77%, 71%, 89%, and 96% respectively in 2022. Rubella seroprevalence increased from 32%, 67%, 76%, and 73% to 93%, 84%, 93%, and 98% across the same age groups. No significant sex-based differences were observed for either infection. The estimated Re declined from 7.4 to 3.6 for measles and from 1.8 to 0.8 for rubella following the MR campaign period. Population immunity improved by 2022, particularly for rubella. However, lower measles seroprevalence among children aged 1-15 years indicates persistent immunity gaps despite high vaccine coverage, highlighting the need for continued surveillance and targeted strategies to achieve measles-rubella elimination in India.