Where did COVID-19 come from?

Viruses infect every species on Earth: animals, plants and even bacteria. A virus can only infect a limited range of species. Typically these are related species, which is why your pets do not get a cold when you have a cold.

Viruses cannot multiply independently, they require a cell to ‘host’ them. When a virus infects a cell that host cell becomes a ‘virus factory’ producing many identical viruses. The host cell eventually ruptures, releasing the viruses which can infect more cells and continue to replicate. On rare occasions, the host cell accidentally creates a change in the virus genetic material (viral DNA) when the viruses are made. Even more rarely, that genetic change means the virus can now infect a new species. When species come in contact the virus can be transmitted between them. This is what we now believed happened at the Huanan Seafood Wholesale Market in Wuhan, Hubei Provence, China in late 2019.

Severe acute respiratory syndrome coronavirus 2 (abbreviated SARS-CoV-2), the virus that causes coronavirus disease 19 (COVID-19), is a ‘novel’ virus because it had not sickened enough people to get our attention until December 2019.

Why is the current COVID-19 outbreak so serious?

Similar to influenza, SARS-CoV-2 is a respiratory virus infecting the nose, sinuses and upper throat. A cough, difficulty breathing and fever arise as the immune system works to identify and eliminate virus-infected cells. Cells not eliminated by the immune system release more viruses to the mucus and fluid of the nose and throat. Some patients develop pneumonia, a viral or bacterial infection of the lung air sacs, which can become life-threatening. The COVID-19 virus spreads through contact with virus-containing mucus and saliva produced when someone sneezes or coughs but also during normal activities, such as talking and transferring virus from our hands to common surfaces. None of these features are particularly special or unique compared to the common cold or influenza viruses. The concerning features, the reason this has become a pandemic, are how easily it spreads through the population.

Why has SARS-CoV-2 been so difficult to contain?

Researchers across the world are working tirelessly to get to know SARS-CoV-2 so we can determine the best measures to protect ourselves and slow the spread of the virus. The incubation period for COVID-19, the time lag between when patients are infected and when they develop noticeable symptoms, is on average 5 days but can last as long as 12 days.(Bai et al., 2020; Lauer et al., 2020; Linton et al., 2020)

A growing body of evidence is making it clear that infected patients are contagious a day or two before they develop symptoms and may be contagious for 2 to 3 weeks after they develop symptoms.(He et al., 2020; Li et al., 2020; Zou et al., 2020)  Some contagious patients never develop symptoms.(Bai et al., 2020; Rothe et al., 2020)

Clearly, quarantine of symptomatic patients is insufficient to contain the spread of COVID-19.

Why is ‘social distancing’ a solution to the spread of COVID-19?

This pandemic has reached the point where the major consideration should be the measures we can individually take to protect ourselves and others. The potential of this pandemic to drain global healthcare and medical supply resources is real.

Limiting the number of people with whom we interact, regardless of whether we feel sick or they feel sick, will help contain the spread of COVID-19. Viral-containing mucus and saliva can be spread through coughs and sneezes, but also during activities such as talking, eating and touching our face. This is why ‘social distancing’ and limiting our direct person-to-person contact is recommended.

Why is it so important to practice thorough hand washing techniques?

Virus can be transferred to the hands of contagious patients when they touch near their mouth and nose, even if they have no symptoms. Viruses on their hands can be transferred to surfaces and objects they touch. Regular, thorough hand washing can prevent contagious people from depositing virus on surfaces and prevent uninfected people from transferring virus picked up on their hands to their face.

Research into the stability of SARS-CoV-2 suggests that the virus is highly stable on plastic and stainless steel, lasting for days. On cardboard and fabric it remains detectable for a day or so. It is least stable on paper products and copper surfaces, becoming undetectable in 3 and 8 hours, respectively.(Chin et al., 2020; Doremalen et al., 2020) Being aware of, and minimizing, the surfaces we touch when we are in public, coupled with washing our hands, will reduce viral spread. To protect ourselves at home, common disinfecting methods are effective against SARS-CoV-2. Disinfecting with a solution of 1 teaspoon household bleach diluted in one cup water can inactivate the virus in 5 mintues.(Chin et al., 2020)

Most striking SARS-CoV-2 appears to be exceptionally stable on surgical masks, remaining detectable for 7 days.(Chin et al., 2020) Based on this finding surgical masks should be handled minimally when worn, and disposed of regularly as medical waste, if possible.

We are not powerless against SARS-CoV-2, we have simple, effective tools and techniques to protect ourselves. Wash your hands with soap, be aware of touching your face and surfaces in public, minimize the number of people with whom you have close contact, and disinfect surfaces, particularly plastic and stainless steel surfaces, if you are concerned.


Bai, Y., Yao, L., Wei, T., Tian, F., Jin, D.-Y., Chen, L., & Wang, M. (2020). Presumed Asymptomatic Carrier Transmission of COVID-19. JAMA. https://doi.org/10.1001/jama.2020.2565

Chin, A., Chu, J., Perera, M., Hui, K., Yen, H.-L., Chan, M., Peiris, M., & Poon, L. (2020). Stability of SARS-CoV-2 in different environmental conditions. MedRxiv, 2020.03.15.20036673. https://doi.org/10.1101/2020.03.15.20036673

Doremalen, N. van, Bushmaker, T., Morris, D., Holbrook, M., Gamble, A., Williamson, B., Tamin, A., Harcourt, J., Thornburg, N., Gerber, S., Lloyd-Smith, J., Wit, E. de, & Munster, V. (2020). Aerosol and surface stability of HCoV-19 (SARS-CoV-2) compared to SARS-CoV-1. MedRxiv, 2020.03.09.20033217. https://doi.org/10.1101/2020.03.09.20033217

He, X., Lau, E. H., Wu, P., Deng, X., Wang, J., Hao, X., Lau, Y. C., Wong, J. Y., Guan, Y., Tan, X., Mo, X., Chen, Y., Liao, B., Chen, W., Hu, F., Zhang, Q., Zhong, M., Wu, Y., Zhao, L., … Leung, G. M. (2020). Temporal dynamics in viral shedding and transmissibility of COVID-19 [Preprint]. Infectious Diseases (except HIV/AIDS). https://doi.org/10.1101/2020.03.15.20036707

Lauer, S. A., Grantz, K. H., Bi, Q., Jones, F. K., Zheng, Q., Meredith, H. R., Azman, A. S., Reich, N. G., & Lessler, J. (2020). The Incubation Period of Coronavirus Disease 2019 (COVID-19) From Publicly Reported Confirmed Cases: Estimation and Application. Annals of Internal Medicine. https://doi.org/10.7326/M20-0504

Li, Q., Guan, X., Wu, P., Wang, X., Zhou, L., Tong, Y., Ren, R., Leung, K. S. M., Lau, E. H. Y., Wong, J. Y., Xing, X., Xiang, N., Wu, Y., Li, C., Chen, Q., Li, D., Liu, T., Zhao, J., Liu, M., … Feng, Z. (2020). Early Transmission Dynamics in Wuhan, China, of Novel Coronavirus–Infected Pneumonia. New England Journal of Medicine. https://doi.org/10.1056/NEJMoa2001316

Linton, N. M., Kobayashi, T., Yang, Y., Hayashi, K., Akhmetzhanov, A. R., Jung, S., Yuan, B., Kinoshita, R., & Nishiura, H. (2020). Incubation Period and Other Epidemiological Characteristics of 2019 Novel Coronavirus Infections with Right Truncation: A Statistical Analysis of Publicly Available Case Data. Journal of Clinical Medicine, 9(2), 538. https://doi.org/10.3390/jcm9020538

Rothe, C., Schunk, M., Sothmann, P., Bretzel, G., Froeschl, G., Wallrauch, C., Zimmer, T., Thiel, V., Janke, C., Guggemos, W., Seilmaier, M., Drosten, C., Vollmar, P., Zwirglmaier, K., Zange, S., Wölfel, R., & Hoelscher, M. (2020). Transmission of 2019-nCoV Infection from an Asymptomatic Contact in Germany. New England Journal of Medicine, 382(10), 970–971. https://doi.org/10.1056/NEJMc2001468

Zou, L., Ruan, F., Huang, M., Liang, L., Huang, H., Hong, Z., Yu, J., Kang, M., Song, Y., Xia, J., Guo, Q., Song, T., He, J., Yen, H.-L., Peiris, M., & Wu, J. (2020). SARS-CoV-2 Viral Load in Upper Respiratory Specimens of Infected Patients. New England Journal of Medicine, 382(12), 1177–1179. https://doi.org/10.1056/NEJMc2001737