Surveillance data

Due to late reporting or under reporting of the cases in the situation reports in the early outbreak (5,32), which is also indicated by (10,13,16), the officially reported time series data of cases will introduce biases into the estimation and simulation without reasonable adjustment for varying reporting rates (19,33,34). Therefore, we adopt the time series of laboratory confirmed cases from Li et al. (15). All cases were laboratory confirmed following the case definition by the National Health Commission of China (35) indicated in (15). Specifically the cases ‘were collected onto standardized forms through interviews of infected persons, relatives, close contacts, and health care workers’, and aggregated by the date of symptoms onset (15). The data should cover most of symptomatic pneumonia of unknown etiology if not all from December 1, 2019 to early January 8, 2020. We choose to use the data up to January 8, one day before the decline of epidemic curve in Figure 1 of (15), for model fitting and parameter estimation. The decline after January 8, 2020 in their figure was ‘likely to be due to delays in diagnosis and laboratory confirmation’ (15).

The estimation of basic reproduction number (R₀) and sensitivity to payoff gain (κ), and the fitting results of the early outbreak. (A,B) likelihood profiles (purple curve) of R₀ and κ, and the cutoff threshold (red dashed line) respectively; (C) comparison between the peak sizes of our simulation (varying with κ) and that of Wu et al. (10); (D) fitting results (curves) to the cases data (blue dots) in Wuhan from Li et al. (15), where the black curve is the simulation median and the grey curves are the 1,000 simulation samples; (E) comparison between our simulation on cumulative number of infections and those from other literatures (9,13,16,17).