Protective antibody response following two doses of measles vaccination and factors for non-response among children from tribal Odisha, India.

Background and objectives Globally, measles cases remain above 10 million despite the introduction of two dose measles vaccination schedule since 2000. India reported 13220 cases during 2023-2024, ranking fourth globally. This raises concern regarding the effectiveness of the ongoing programme to achieve measles elimination. Tribal dominated regions in countries such as India needs particular attention due to their higher burden of childhood morbidity and mortality. This study aimed to estimate the proportion of children developing protective antibody levels following two doses of measles vaccine in a tribal location and to identify potential risk factors associated with non-response. Methods A tribal dominated region, the undivided Phulbani district of Odisha, India, was randomly selected. Using cluster sampling, 1375 Infants aged 8 months were enrolled from 30 tribal habitations and followed to document vaccination status. Blood samples (n=1185) were collected three months after the second measles vaccine dose, and their measles IgG antibody levels were quantified. Variables likely to influence antibody response were recorded and statistically evaluated. Results Two-dose measles vaccine coverage was 99.6%; however, 55.1% (n=653) of children demonstrated seropositivity (IgG titre ≥ 250 IU/L). Male gender was significantly associated with suboptimal antibody response. Age, nutritional status, interval between first and second vaccine doses, and vaccination logistics were not found to influence antibody response. Interpretation and conclusion This study provides the first evidence of suboptimal measles antibody response among children from a tribal area of Odisha, India, despite high vaccination coverage. There is a need to understand the immune persistence among such a vulnerable population, where measles control remains a challenge.