Social distancing strategies for curbing the COVID-19 epidemic

Stephen M Kissler; Christine Tedijanto; Marc Lipsitch; Yonatan Grad

We evaluated the impact of one-time social distancing efforts of varying effectiveness and duration on the peak and timing of the epidemic with and without seasonal forcing. When transmission is not subject to seasonal forcing, one-time social distancing measures reduce the epidemic peak size (Figure 1, Figure S4 ). Under all scenarios, there was a resurgence of infection when the simulated social distancing measures were lifted. However, longer and more stringent social distancing did not always correlate with greater reductions in epidemic peak size. In the case of a 20-week period of social distancing with 60% reduction in R0, for example, the resurgence peak size is nearly the same as the peak size of the uncontrolled epidemic: the social distancing is so effective that virtually no population immunity is built. The greatest reductions in peak size come from social distancing intensity and duration that divide cases approximately equally between peaks (12) .