3.2 High infectivity (Why is COVID-19 so infectious?)

1. Molecular Level: SARS-CoV-2 utilizes the same cellular receptors as SARS-CoV, the human Angiotensin Converting Enzyme 2 (hACE2). Therefore, it is expected that this new virus would behave similar to SARS-CoV in terms of transmission properties, such as causing lower instead of upper respiratory tract symptoms. However, unlike SARS-CoV or MERS-CoV, epithelial cells in human airway are more suitable than standard tissue culture medium for the growth of SARS-CoV-2. 

2. Long Incubation Period & Asymptomatic Transmission: The incubation period of SARS-CoV-2 is up to 24 days and the virus is capable of human-to-human transmission among asymptomatic individuals or those displaying only mild symptoms. Unlike SARS in which most patients developed fever, a very large study involving 1,099 COVID-19 patients showed only 43.8% of them had fever at the time of admission. This renders comprehensive early identification of cases via temperature screening extremely difficult. 

3. Low CFR: People would be more complacent and less compliant to preventive measures.

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Habibzadeh P & Stoneman EK (2020): The Novel Coronavirus: A Bird’s Eye View. The International Journal of Occupational and Environmental Medcine 11: 65-71.
Rothe C, Schunk M, Sothmann P, et al. (2020): Transmission of 2019-nCoV Infection from an Asymptomatic Contact in Germany. New England Journal of Medicine 382: 970-971.