Fig. 1

Illustration of the effect of seasonality on timing of malaria infections, and the benefit of post-treatment prophylaxis. EIR entomological inoculation rate, PTP post-treatment prophylaxis. Simplified representation of the effect of seasonality on timing of malaria infections. Sites A and B have the same annual EIR (6 infections per person per year). However, the monthly EIR in the seasonal setting (scenario B) is twice that in the perennial setting (scenario A). The monthly EIR during the transmission season in site B is the same as a perennial setting with an annual EIR of 12 (site C). Due to post-treatment prophylaxis provided by case-management for malaria, some malaria infections that occur soon after a previous episode will be prevented. This is more likely to occur where infection rates are higher, and where malaria infections occur close together in time. In seasonal settings, the length of PTP also becomes large in relation to the length of the season. This suggests that seasonal settings may have more preventable malaria than perennial settings with an equivalent annual EIR. Additional complications dealt with in this paper include realistic seasonality patterns, heterogeneity in malaria risk between individuals, immunity (acquisition of which may differ in seasonal and non-seasonal settings) and variable duration of protection from drugs used for case-management