Sentinel serosurvey for Mpox virus infection among key populations in India: Evidence of sporadic past exposure beyond travel-related cases

Background and objectives Mpox, declared a public health emergency of international concern by WHO, has demonstrated sporadic transmission globally. While India reported 66 confirmed cases predominantly linked to international travel, the possibility of silent community circulation remains unconfirmed, particularly within high-risk populations. Serological surveys are crucial for detecting past exposure, including asymptomatic infections that may be missed by clinical surveillance. This study aimed to assess the prevalence of anti-MPXV IgG and IgM antibodies and identify socio-demographic and behavioural determinants of seropositivity among key populations in India. Methods A multicentric, cross-sectional sentinel serosurvey was conducted between September 2023 to March 2024 across seven community-based organisation sites in India. A total of 1,790 participants aged 18-40 y (born after cessation of smallpox vaccination in India) were enrolled. Serological testing was performed using enzyme-linked immunosorbent assay (ELISA) for anti-MPXV IgG and IgM antibodies. Plaque reduction neutralisation test (PRNT50) was used to assess functional neutralising antibodies against both MPXV and Vaccinia virus. Results Among 1,790 participants, 14 (0.78%) tested positive for anti-MPXV IgG, with no IgM positivity detected. IgG-positive individuals were predominantly male (57.1%), aged 31-40 y (85.7%), and sexually active (75.9%). Geographic distribution ranged from 0.34% (Delhi NCR) to 2.07% (Kerala). PRNT50 assay revealed functional neutralising antibodies against MPXV in 64.3% (9/14) of IgG-positive samples, with evidence of cross-reactive immunity to Vaccinia virus in 93.9% (13/14). Interpretation and conclusions This multicentric sentinel serosurvey identified very low Mpox virus seroprevalence (0.78%) among key populations in India, suggesting limited prior exposure. The absence of IgM antibodies indicates that infections were not recent and provides no evidence of ongoing community transmission during the study period. Detection of neutralising antibodies in a subset of IgG-positive individuals supports prior Orthopoxvirus exposure. These findings establish baseline sero-epidemiological evidence for Mpox in India and underscore the importance of periodic sentinel sero surveillance for early detection and outbreak preparedness.