In Sydney 1919, the attack rate must have lain between these extremes: a min % a% a max . Based on the difference between our estimates of a and a max , we scale up the number of lives actually lost to estimate how many lives might have been lost if the epidemic had been entirely unimpeded by social distancing. By this measure, the number of deaths per 100 000 of the population that were prevented by social distancing (D) was DZ ða max =a K1Þp !10 5 .