Dengue and chikungunya virus epidemiology and vaccine considerations in the Democratic Republic of the Congo

Dengue virus (DENV) and chikungunya virus (CHIKV) are increasingly recognized as important public health threats across Africa, yet their epidemiology is poorly understood, partly due to limited surveillance and diagnostics, and overlapping clinical symptoms with highly prevalent illnesses such as malaria, complicating disease differentiation. In the Democratic Republic of the Congo (DRC), evidence of transmission exists, but prevalence and transmission dynamics remain uncertain. Further, absence of African countries in dengue vaccine trials limits understanding of expected vaccine performance in these settings, where transmission dynamics, baseline risks, demographics, circulating serotypes, and co-circulating flaviviruses likely differ from trial populations. In the DRC, documented outbreaks and past infections, alongside limited epidemiological data highlight the need to quantify disease burden and identify at-risk populations to inform intervention strategies. In Aim 1, we analyzed samples from a cross-sectional study of 1,250 children and adults in Kinshasa, DRC using antigen-capture ELISA, and detected a 38.1% (95% CI: 34.5%-41.8%) seroprevalence of DENV IgG, and 24.2% (95% CI: 21.1%-27.6%) seroprevalence of CHIKV IgG. Seroprevalences varied by age and location. Catalytic force of infection (FOI) modeling indicated sustained DENV transmission (FOI: 0.022 [95% CrI: 0.020–0.025]), and sporadic CHIKV transmission, with distinct spatial heterogeneity between viruses. In Aim 2, we applied FOI estimates to model DENV vaccine impact in Kinshasa, representing a lower-endemicity setting, using epidemiological transportability methods within a Monte Carlo simulation calibrated to TAK-003 vaccine Phase 3 trial data and Kinshasa population inputs. Trial-derived hazard ratios were transported across effect modifiers under varying uncertainty scenarios. Overall vaccine effectiveness was similar between simulated trial and target populations in primary analyses; results among children aged 4-5 years suggested uncertainty in vaccine impact, and the number needed to vaccinate was higher in the target population, reflecting lower baseline DENV risks. These findings demonstrate DENV and CHIKV are prevalent in Kinshasa, with spatial heterogeneity and ongoing transmission, and demonstrate how transportability methods could pragmatically generate evidence of vaccine impact in understudied, lower-endemicity settings. Results underscore a need to strengthen arboviral surveillance in the DRC and represent first steps towards addressing gaps in dengue vaccine evidence within lower-endemicity African populations.