  The novel coronavirus (2019-nCoV) is a recently emerged human pathogen that
has spread widely since January 2020. Initially, the basic reproductive number,
R0, was estimated to be 2.2 to 2.7. Here we provide a new estimate of this
quantity. We collected extensive individual case reports and estimated key
epidemiology parameters, including the incubation period. Integrating these
estimates and high-resolution real-time human travel and infection data with
mathematical models, we estimated that the number of infected individuals
during early epidemic double every 2.4 days, and the R0 value is likely to be
between 4.7 and 6.6. We further show that quarantine and contact tracing of
symptomatic individuals alone may not be effective and early, strong control
measures are needed to stop transmission of the virus.
