Multi-pathogen serosurveillance in Tonga examining demographic correlates and geographic clustering of 17 pathogens

Integrated serosurveillance enables concurrent assessment of population immunity to vaccine-preventable diseases (VPDs) and infectious pathogens. We aimed to estimate seroprevalence of antibodies (Abs) to 17 pathogens to provide insights to inform public health strategies to control and eliminate infectious diseases in Tonga. A targeted cross-sectional survey was conducted in May-July 2024 among participants aged ≥ 5 years from Tongatapu, Ha'apai, and Ongo Niuas. Dried blood spots were collected and assayed on a multiplex bead assay (MBA) containing 26 antigens from 17 pathogens. Seropositivity was defined using antigen-specific cut-offs. Associations with seropositivity were assessed, and geographic clustering was investigated. 1,786 of 1,787 (98.9%) participants (median age 19 years; 46% male) had valid MBA results. In our target population, LF Ab seropositivity increased with age, with high seroprevalence in Ha'apai (Wb123 Ab: 13.1%; Bm14 Ab: 8.8%). Dengue seroprevalence was > 90% among > 50-year-olds and were highest in Tongatapu. Seroprevalence for VPD was high; however, measles seroprevalence (86.1%) was below theoretical elimination thresholds despite historically high vaccination coverage. Geographic clustering was significant (p < 0.01) for most pathogens, with strongest clustering seen at village-level. Clear demographic and geographic correlates of seroprevalence in this target population highlight focal transmission and potential immunity gaps. MBA platforms offer a cost-effective tool to support targeted elimination strategies and vaccination campaigns in the Pacific.