The effect of the timing of treatment rounds relative to seasonal peaks in transmission by blackfly vectors on programme duration under strategies of annual community-directed treatment with ivermectin (aCDTI) and annual community-directed treatment with moxidectin (aCDTM). The time between treatment and the peak of transmission was varied. The x-axis represents the number of months between treatment at time 0 and the peak of transmission. Scenario 1: transmission only takes place during a five month long rainy season. Scenario 2: high levels of transmission during a five month long rainy season but continuing at a low level during the rest of the year (Table 1 and Additional file 1: Figure S1). The green, blue and red lines correspond to, respectively, a pre-control endemicity level of 40%, 60%, and 80% microfilarial prevalence. The years are those needed to reach the pOTTIS (<1.4% microfilarial prevalence). The lines show the mean microfilarial load per mg of skin after 15 years of treatment in those aged ≥ 20 years. Solid and dashed lines indicate aCDTI and aCDTM respectively. Modelling assumptions are as in the legend of Figure 2.