Fig. 3: Risk of resurgence after lifting controls.

We consider the main model (M) and the sensitivity analysis (S8) (Methods). In model M, we assume the initial ascertainment rate r₀ = 0.23, and thus an overall ascertainment rate of 0.13. In S8, we assume no unascertained cases initially and thus an overall ascertainment rate of 0.47. For each model, we simulated epidemic curves on the basis of 10,000 sets of parameters from MCMC, and set the transmission rate (b), ascertainment rate (r) and population movement (n) to their values in the first period after lifting controls. Resurgence was defined as reaching over 100 active ascertained infections. a, Illustration of a simulated curve under the main model, with control measures lifted 14 days after the first day of no ascertained cases. The inset is an enlarged plot from 16 March to 28 May. b, Probability of resurgence if control measures were lifted t days after the first day of no ascertained cases, or after observing zero ascertained cases for t days consecutively. c, Expectation of time to resurgence, conditional on the occurrence of resurgence. We grouped the final 10 days (t = 21 to 30) to calculate the expected time to resurgence because of their low probability of resurgence. Key applies to both b and c.