We identified 12 studies which estimated the basic reproductive number for COVID-19 from China and overseas. Table 1 shows that the estimates ranged from 1.4 to 6.49, with a mean of 3.28, a median of 2.79 and interquartile range (IQR) of 1.16.
Published estimates of R0 for 2019-nCoV
|Study (study year)||Location||Study date||Methods||Approaches||R0estimates (average)||95% CI|
|Joseph et al.1||Wuhan||31 December 2019–28 January 2020||Stochastic Markov Chain Monte Carlo methods (MCMC)||MCMC methods with Gibbs sampling and non-informative flat prior, using posterior distribution||2.68||2.47–2.86|
|Shen et al.2||Hubei province||12–22 January 2020||Mathematical model, dynamic compartmental model with population divided into five compartments: susceptible individuals, asymptomatic individuals during the incubation period, infectious individuals with symptoms, isolated individuals with treatment and recovered individuals||R0 = β/αβ = mean person-to-person transmission rate/day in the absence of control interventions, using nonlinear least squares method to get its point estimateα = isolation rate = 6||6.49||6.31–6.66|
|Liu et al.3||China and overseas||23 January 2020||Statistical exponential Growth, using SARS generation time = 8.4 days, SD = 3.8 days||Applies Poisson regression to fit the exponential growth rateR0 = 1/M(−𝑟)M = moment generating function of the generation time distributionr = fitted exponential growth rate||2.90||2.32–3.63|
|Liu et al.3||China and overseas||23 January 2020||Statistical maximum likelihood estimation, using SARS generation time = 8.4 days, SD = 3.8 days||Maximize log-likelihood to estimate R0 by using surveillance data during a disease epidemic, and assuming the secondary case is Poisson distribution with expected value R0||2.92||2.28–3.67|
|Read et al.4||China||1–22 January 2020||Mathematical transmission model assuming latent period = 4 days and near to the incubation period||Assumes daily time increments with Poisson-distribution and apply a deterministic SEIR metapopulation transmission model, transmission rate = 1.94, infectious period =1.61 days||3.11||2.39–4.13|
|Majumder et al.5||Wuhan||8 December 2019 and 26 January 2020||Mathematical Incidence Decay and Exponential Adjustment (IDEA) model||Adopted mean serial interval lengths from SARS and MERS ranging from 6 to 10 days to fit the IDEA model,||2.0–3.1 (2.55)||/|
|WHO||China||18 January 2020||/||/||1.4–2.5 (1.95)||/|
|Cao et al.6||China||23 January 2020||Mathematical model including compartments Susceptible-Exposed-Infectious-Recovered-Death-Cumulative (SEIRDC)||R = K 2 (L × D) + K(L + D) + 1L = average latent period = 7,D = average latent infectious period = 9,K = logarithmic growth rate of the case counts||4.08||/|
|Zhao et al.7||China||10–24 January 2020||Statistical exponential growth model method adopting serial interval from SARS (mean = 8.4 days, SD = 3.8 days) and MERS (mean = 7.6 days, SD = 3.4 days)||Corresponding to 8-fold increase in the reporting rateR0 = 1/M(−𝑟)𝑟 =intrinsic growth rateM = moment generating function||2.24||1.96–2.55|
|Zhao et al.7||China||10–24 January 2020||Statistical exponential growth model method adopting serial interval from SARS (mean = 8.4 days, SD = 3.8 days) and MERS (mean = 7.6 days, SD = 3.4 days)||Corresponding to 2-fold increase in the reporting rateR0 = 1/M(−𝑟)𝑟 =intrinsic growth rateM = moment generating function||3.58||2.89–4.39|
|Imai (2020)8||Wuhan||January 18, 2020||Mathematical model, computational modelling of potential epidemic trajectories||Assume SARS-like levels of case-to-case variability in the numbers of secondary cases and a SARS-like generation time with 8.4 days, and set number of cases caused by zoonotic exposure and assumed total number of cases to estimate R0values for best-case, median and worst-case||1.5–3.5 (2.5)||/|
|Julien and Althaus9||China and overseas||18 January 2020||Stochastic simulations of early outbreak trajectories||Stochastic simulations of early outbreak trajectories were performed that are consistent with the epidemiological findings to date||2.2|
|Tang et al.10||China||22 January 2020||Mathematical SEIR-type epidemiological model incorporates appropriate compartments corresponding to interventions||Method-based method and Likelihood-based method||6.47||5.71–7.23|
|Qun Li et al.11||China||22 January 2020||Statistical exponential growth model||Mean incubation period = 5.2 days, mean serial interval = 7.5 days||2.2||1.4–3.9|
CI, Confidence interval.
The first studies initially reported estimates of R0 with lower values. Estimations subsequently increased and then again returned in the most recent estimates to the levels initially reported (Figure 1).