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In December 2019, clusters of pneumonia cases have been reported in Wuhan, Hubei Province, China. High-throughput sequencing analysis from lower respiratory tract of patients has revealed that the causing agent was a novel coronavirus. In January 2020, the World Health Organization (WHO) named the new corona virus as the 2019 novel coronavirus (2019‐nCoV) and announced the 2019‐nCoV epidemic a public health emergency of international concern. In February 2020, the WHO named the disease caused by 2019‐nCoV as coronavirus disease 2019 (COVID‐ 19) and International Committee on Taxonomy of Viruses (ICTV) named 2019‐nCoV as severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐ 2).

Coronaviruses belong to the Coronaviridae family and it represents crown-like spikes on the outer surface of the virus; therefore, it is named as a coronavirus [1]. SARS-CoV-2 is the seventh member of the coronavirus family that infects human beings after SARS-CoV and MERS-CoV [2, 3]. Coronavirus through the S protein on its surface recognizes the corresponding receptor on the target cell and enters the cell, leading to the occurrence of infection [4]. R0 which represents the number of cases that directly transmitted by one case  is estimated to be 2.47-2.86 for SARS-CoV-2 [5]. The R0 value of other coronaviruses such as SARS-CoV and  MERS-CoV estimated to be 2.2-3.6 and 2.0-6.7, respectively [6, 7]. This indicates that SARS-CoV-2 has relatively high transmissibility.  

The average incubation period which is the time from infection to illness onset reported to be 4 days [8]. Based on the incubation period of SARS-CoV and MERS-CoV, as well as available data for SARS-CoV-2, it was estimated that symptoms of COVID-19 will usually develop within 2–14 days after exposure [9]. Therefore, 14 days has been considered internationally for monitoring and restricting the movement of healthy individuals [10].


1.        Shereen, M.A., et al., COVID-19 infection: origin, transmission, and characteristics of human coronaviruses. Journal of Advanced Research, 2020.

2.        Li, H., et al., Coronavirus disease 2019 (COVID-19): current status and future perspective. International Journal of Antimicrobial Agents, 2020: p. 105951.

3.        Zheng, J., SARS-CoV-2: An emerging coronavirus that causes a global threat. International Journal of Biological Sciences, 2020. 16(10): p. 1678.

4.        Walls, A.C., et al., Structure, function, and antigenicity of the SARS-CoV-2 spike glycoprotein. Cell, 2020.

5.        Wu, J.T., K. Leung, and G.M. Leung, Nowcasting and forecasting the potential domestic and international spread of the 2019-nCoV outbreak originating in Wuhan, China: a modelling study. The Lancet, 2020. 395(10225): p. 689-697.

6.        Lipsitch, M., et al., Transmission dynamics and control of severe acute respiratory syndrome. Science, 2003. 300(5627): p. 1966-1970.

7.        Majumder, M.S., et al., Estimation of MERS-coronavirus reproductive number and case fatality rate for the spring 2014 Saudi Arabia outbreak: insights from publicly available data. PLoS Currents, 2014. 6.

8.        Guan, W.-j., et al., Clinical characteristics of coronavirus disease 2019 in China. New England Journal of Medicine, 2020.

9.        Backer, J.A., D. Klinkenberg, and J. Wallinga, Incubation period of 2019 novel coronavirus (2019-nCoV) infections among travellers from Wuhan, China, 20–28 January 2020. Eurosurveillance, 2020. 25(5): p. 2000062.

10.      Hussain, A., B. Bhowmik, and N.C. do Vale Moreira, COVID-19 and diabetes: knowledge in progress. Diabetes Research and Clinical Practice, 2020: p. 108142.

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