Impact of switching to biannual community-directed treatment with ivermectin (bCDTI) or annual community-directed treatment with moxidectin (aCDTM) at different stages of an ongoing annual CDTI (aCDTI) programme. The green, blue and red bars correspond to a pre-control endemicity level of 40%, 60%, and 80% microfilarial prevalence, respectively. The aCDTI, bCDTI and aCDTM strategies are indicated by solid, dashed and dotted bars, respectively. Error bars represent the results of varying the provisional operational thresholds for treatment interruption followed by surveillance (pOTTIS) by ± 0.5%. The number of additional years of treatment and the ratio of additional costs are considered from the point of switching to bCDTI or aCDTM (and not from the start of control). Modelling assumptions are as in the legend of Figure 2. *pOTTIS (1.4% microfilarial prevalence) not attained within the 50-year time horizon and percentage of costs calculated based on costs of 50 years of aCDTI. † Costs do not include value of the (donated) drugs.