Impact of policy and multiplicity of infection (MOI) on useful therapeutic life; the latter is plotted on the Y axis and is defined as the number of parasite generations that elapse before overall drug failure rates reach 10%. It is plotted as a function of drug usage (the proportion of infections that are treated) on the X-axis. The chart compares combination therapy (CT), MFT and sequential (Seq) deployment policies with MOIs of 2 and 4 and with a fitness penalty of 10%. MFT and CT perform better than sequential policies at lower drug usage but MFT marginally worse with high drug usage. All three deployment policies last longer with lower MOIs. (A) Two drugs are available. (B) Three drugs are available; the lines start abruptly because for lower drug usage the policies last longer than the 200 generations simulated.