Introduction
2019 Novel coronavirus (2019-nCoV/SARS-CoV-2) has given rise to an outbreak of viral pneumonia in Wuhan, China since December 20191,2. World Health Organization (WHO) now has named the disease Coronavirus Disease 2019 (COVID-19)3. Most cases from the initial cluster had an epidemiological link to the Huanan Seafood Wholesale Market4. Patients have clinical manifestations, including fever, cough, shortness of breath, muscle ache, confusion, headache, sore throat, rhinorrhoea, chest pain, diarrhea, and nausea and vomiting5,6. As of 17 February 2020, a cumulative total of 72,436 confirmed cases (including 11,741 currently severe cases), 6242 currently suspect cases, a cumulative total of 1868 deaths and 12,552 cases discharged from hospital were reported by National Health Commission of the People’s Republic of China (NHC) in mainland China7. The significant increases in the number of confirmed cases in China and abroad led to the announcement made by WHO on 30 January that the event has already constituted a Public Health Emergency of International Concern8.
The reproduction number, R, measures the transmissibility of a virus, representing the average number of new infections generated by each infected person, the initial constant of which is called the basic reproduction number, R09, and the actual average number of secondary cases per infected case at time t is called effective reproduction number, Rt10–12. Rt shows time-dependent variation with the implementation of control measures. R > 1 indicates that the outbreak is self-sustaining unless effective control measures are implemented, while R < 1 indicates that the number of new cases decreases over time and, eventually, the outbreak will stop9. Over the past month, several groups reported estimated R0 of COVID-19 and generated valuable prediction for the early phase of this outbreak. In particular, Imai et al.9 provided the first estimation, using R0 of 2.6 and based on the number of cases in China and those detected in other countries. Other authors estimated R0 to be 3.813, 6.4714, 2.215, and 2.6816. These predictions were very alerting and suggestions have been made for very strict public health measures to contain the epidemics.
In response to the outbreak of COVID-19, a series of prompt public health measures have been taken. On 1 January, the Huanan Seafood Wholesale Market was closed in the hope of eliminating zoonotic source of the virus5. On 11 January, upon isolation of the viral strain for COVID-19 and establishment of its whole-genome sequences17, reverse transcription-polymerase chain reaction (RT-PCR) reagents were developed and provided to Wuhan, which ensured the fast ascertainment of infection15. On 21 January, Emergency Response System was activated to better provide ongoing support to the COVID-19 response18. Ever since the outbreak, the work of intensive surveillance, epidemiological investigations, and isolation of suspect cases gradually improved. Those having had close contacts with infections were asked to receive medical observation and quarantine for 14 days19. Travel from and to Wuhan City as well as other medium-sized cities in Hubei Province has been restricted since 23 January 202020.
The 2019-nCoV/SARS-CoV-2 has at least 79.5% similarity in genetic sequence to SARS-CoV5,17. Riley21 estimated that 2.7 secondary infections were generated per case on average (R0 = 2.7) at the start of the SARS epidemic without controlling. After isolating the patients and controlling the infection by the authority, the value of Rt for SARS decreased to 0.2522. As Li et al.15 mentioned, it is possible that subsequent control measures in Wuhan, and elsewhere in mainland China, have reduced transmissibility. A new estimation of the epidemic dynamics taking the unprecedentedly strict prevention and control measures in China into consideration is required to better guide the future prevention decisions.
In this article, we intended to make phase-adjusted estimation of the epidemic trend for the 2019-nCoV / SARS-CoV-2 infection transmission in Wuhan, China under two assumptions of Rt (maintaining high >1 or gradually decreasing to <1). We hope to depict two types of epidemic dynamics to provide potential evaluation standard for the effects of current prevention and control measures, and to provide theoretical basis for future prevention decisions of the current epidemic in China.