Reducing the antigen prevalence target threshold for stopping and restarting mass drug administration for lymphatic filariasis elimination: a model-based cost-effectiveness simulation in Tanzania, India, and Haiti

Background: The Global Programme to Eliminate Lymphatic Filariasis (GPELF) aims to reduce and maintain infection levels through mass drug administration (MDA), but there is evidence of ongoing transmission post-MDA in areas where Culex mosquitoes are the main transmission vector, suggesting that a more stringent criteria is required for MDA decision-making in these settings. Methods: We use a transmission model to investigate how a lower prevalence threshold (<1% antigenemia (Ag) prevalence compared to <2% Ag prevalence) for MDA decision-making would impact the probability of local elimination, health outcomes, the number of MDA rounds including restarts, and programme costs associated with MDA and surveys across different scenarios. To determine the cost-effectiveness of switching to a lower threshold, we simulated 65% and 80% MDA coverage of the total population for different willingness to pay per DALY averted: India (US dollars 446.07), Tanzania (US dollars 389.83) and Haiti (US dollars 219.84). Results: Our results suggest that with a lower Ag threshold, there is a small proportion of simulations where extra rounds are required to reach the target, but this also reduces the need to restart MDA later in the programme. For 80% coverage, the lower threshold is cost-effective across all baseline prevalences for India, Tanzania and Haiti. For 65% MDA coverage, the lower threshold is not cost-effective due to additional MDA rounds, although it increases the probability of local elimination. Valuing the benefits of elimination to align with the GPELF goals, we find that a willingness to pay per capita government expenditure of approximately $1000 - $4000 for 1% increase in the probability of local elimination would be required to make a lower threshold cost-effective. Conclusions: Lower Ag thresholds for stopping MDAs generally mean a higher probability of local elimination, reducing long-term costs and health impacts. However, they may also lead to an increased number of MDA rounds required to reach the lower threshold and, therefore, increased short-term costs. Collectively, our analyses highlight that lower target Ag thresholds have the potential to assist programmes in achieving lymphatic filariasis goals.