Impact of mass drug administration campaigns depends on interaction with seasonal human movement
Mass drug administration (MDA) is a control and elimination tool for treating infectious diseases. For malaria, it is widely accepted that conducting MDA during the dry season results in the best outcomes. However, seasonal movement of populations into and out of MDA target areas is common in many places and could potentially fundamentally limit the ability of MDA campaigns to achieve elimination.
A mathematical model was used to simulate malaria transmission in two villages connected to a high-risk area into and out of which 10% of villagers traveled seasonally. MDA was given only in the villages. Prevalence reduction under various possible timings of MDA and seasonal travel was predicted.
The success of MDA is strongly dependent on the timing of travel and transmission in the high-risk area. (A) The percentage reduction in malaria prevalence 1 y after MDA compared with 1 y prior to MDA is greatest when MDA occurs during the low-transmission season in the villages and does not overlap with travel to the high-risk area (small left and right boxes) and is least when MDA occurs while travelers are away and traveling overlaps at least 3 months with peak transmission in the high-risk area (central box). The impact of mistimed MDA is (B) greatest in travelers but (C) is also felt in non-travelers. In all panels, MDA is with DP and consists of two rounds separated by 60 d.
Seasonal movement patterns of high-risk groups should be taken into consideration when selecting the optimum timing of MDA campaigns.