We consider the effects of clustering on the efficacy of contact tracing using pairwise models by starting the system at the endemic state in the absence of any contact tracing. We then introduce tracing at a success probability e, and allow the system to evolve away from the endemic state for 0.1 and one generations (time periods 1=(10g) and 1=g respectively, corresponding to policy evaluation after a number of months and a number of years for an endemic STI) and measure the numbers infectious. This gives the results in Figure 4 , which show that clustering increases the efficacy of contact tracing at a given success rate at one infectious generation, but not at 0.1 generations, depending on the actual tracing success rate. Pane C shows this variety of responses, where clustering is more effective for large success rates at this small time-the very large rates require still smaller times to demonstrate this effect, since after 0.1 disease generations they have passed into the regime where clustering leads to less effective tracing.