Social distancing strategies for curbing the COVID-19 epidemic

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

The model we have used is deterministic and assumes that the population is well-mixed, meaning that each person has an equal probability of coming into potentially infectious contact with every other person. Population structure can reduce outbreak peak size (17) , so the modeling here may be interpreted as worst-case scenarios. The timing and duration of the interventions will likely need to be tailored geographically due to variation in epidemic timing, seasonal forcing, and critical care capacities. Deterministic models also cannot capture the possibility of SARS-CoV-2 elimination. However, given the widespread transmission of SARS-CoV-2, we believe that elimination is unlikely. Re-introductions of SARS-CoV-2 from locations with ongoing outbreaks would be sufficient to initiate sustained local transmission again (18) . We have also assumed that SARS-CoV-2 infection is permanently immunizing, since our focus was on the initial pandemic period. There is insufficient serological data to assess the amount of immunity that exists to SARS-CoV-2 and its duration. If SARS-CoV-2 immunity wanes rapidly, social distancing measures may need to be extended longer. However, if there are many undocumented asymptomatic infections that lead to immunity (19) , less social distancing may be required. Social distancing strategies will require further evaluation as longitudinal serological studies clarify the extent and duration of immunity to SARS-Cov-2.