Modeling the impact and costs of semiannual mass drug administration for accelerated elimination of lymphatic filariasis

Abstract

The Global Program to Eliminate Lymphatic Filariasis (LF) has a target date of 2020. This program is progressing well in many countries. However, progress has been slow in some countries, and others have not yet started their mass drug administration (MDA) programs. Acceleration is needed. We studied how increasing MDA frequency from once to twice per year would affect program duration and costs by using computer simulation modeling and cost projections. We used the LYMFASIM simulation model to estimate how many annual or semiannual MDA rounds would be required to eliminate LF for Indian and West African scenarios with varied pre-control endemicity and coverage levels. Results were used to estimate total program costs assuming a target population of 100,000 eligibles, a 3% discount rate, and not counting the costs of donated drugs. A sensitivity analysis was done to investigate the robustness of these results with varied assumptions for key parameters. Model predictions suggested that semiannual MDA will require the same number of MDA rounds to achieve LF elimination as annual MDA in most scenarios. Thus semiannual MDA programs should achieve this goal in half of the time required for annual programs. Due to efficiency gains, total program costs for semiannual MDA programs are projected to be lower than those for annual MDA programs in most scenarios. A sensitivity analysis showed that this conclusion is robust. Semiannual MDA is likely to shorten the time and lower the cost required for LF elimination in countries where it can be implemented. This strategy may improve prospects for global elimination of LF by the target year 2020.

Figure 1. Simulated trends in mf prevalence (%) after mass drug administration.

The presented trends are for an African setting with pre-control mf prevalence around 20%, where 6 rounds of annual mass drug administration with IVM+ALB were provided starting at time 0. Coverage was 70% and drug efficacy was quantified according to our baseline assumptions. The figure displays the trend of 25 runs, simulated by LYMFASIM, all with the same input assumptions. Variation in the outcomes is due to stochasticity.

Figure 2. Probability of elimination in relation to the duration of mass drug administration.

Panel A shows the results for an Indian setting with a pre-control mf prevalence of about 11.5%, for annual and semiannual mass drug administration and for different coverage levels (percentage of the total population that is treated per round). Similarly, panel B shows the results for an African setting with a pre-control mf prevalence of about 20%. The indicated mf prevalence levels are for diagnosis with 60 µL night blood smears.