Examining epidemiological models and economic analyses of typhoid conjugate vaccine: A scoping review

Typhoid remains a public health concern across many low- and middle-income countries. This scoping review summarized and mapped evidence from epidemiological models and economic analyses of typhoid conjugate vaccine (TCV). We included studies on the cost of illness of typhoid, the cost of vaccination, cost-effectiveness, and public health impact of TCV. A search was conducted across five databases and followed the Arksey and O'Malley's methodological framework. We extracted data on the study design, population, outcomes, model parameters, and cost-effectiveness. All reported costs were converted to 2024 United States Dollars (USD) to allow for comparisons across studies. Findings were summarized by key outcomes. The 26 studies included in the review covered Sub-Saharan Africa, South and East Asia, the Pacific, Latin America, the Middle East, and Europe. A total of ten studies reported the cost of treating a typhoid patient, with costs varying based on the hospital setting, geographic location and severity of the disease. Five studies examined the cost of TCV vaccination and delivery reported higher costs for campaigns than routine immunization, with economic costs consistently higher than financial costs. The two public health impact studies predicted case reductions from 2% to 94% and mortality reductions up to 36% or 100%, depending on the vaccine strategy employed. The nine economic evaluations included in the review reported lower incremental cost effectiveness ratios in high-incidence urban settings, with some strategies termed as cost-saving. Cost-effectiveness depends on incidence, perspective, and vaccine strategy, emphasizing the need for context-specific evaluations. Literature shows that the value of TCV is influenced by the disease burden, vaccination costs, and health outcomes, which are context specific. Future research should employ more comprehensive models to better capture TCV's economic and public health value and leverage on local data to give more contextual evidence for policymakers.