Under optimal social distancing with a minimum possible attack rate ðaZ sð0Þ K 1=R 0 Þ, we expect R(N) to be unity. In epidemics where transmission is unimpeded (s(t)Z1 throughout), epidemic decline is much more rapid. During the final phase, there are sufficient infectious cases in that many susceptibles are infected, even though the reproduction number is well below 1.