We estimated that there were a total of 114,325 COVID-19 cases (interquartile
range [IQR] 76,776 - 164,576) in mainland China as of February 29, 2020, and
these were highly correlated (p<0.001, R2=0.86) with reported incidence.
Without NPIs, the number of COVID-19 cases would likely have shown a
67-fold increase (IQR: 44 - 94), with the effectiveness of different interventions
varying. The early detection and isolation of cases was estimated to prevent
more infections than travel restrictions and contact reductions, but integrated
NPIs would achieve the strongest and most rapid effect. If NPIs could have
been conducted one week, two weeks, or three weeks earlier in China, cases
could have been reduced by 66%, 86%, and 95%, respectively, together with
significantly reducing the number of affected areas