An introduction to SARS-CoV-2

Printer Friendly, PDF & Email

The emergence of a novel coronavirus in late 2019, now identified as SARS-CoV-2, has resulted in a global pandemic with an unprecedented public health response. This brief review of the properties of SARS-CoV-2 and how it is transmitted outlines some of the evidence that currently forms the basis of our evolving public health response to COVID-19. The evolving evidence on the dominant routes of transmission, and potential importance of pre-symptomatic and asymptomatic transmission indicate that preventing the spread of the SARS-CoV-2 virus requires a suite of precautionary measures.  As new evidence and new interpretations evolve, this document will be updated.


What is COVID-19? 

Coronavirus disease (COVID-19) is an illness caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a recently discovered novel coronavirus. Coronaviruses are genetically distinct from viruses that cause influenza. They are enveloped, single-stranded RNA viruses whose surface is covered by a halo of protein spikes, or “corona.” Other coronaviruses that have caused significant and lethal outbreaks in the past 20 years include SARS-CoV-1 and MERS-CoV that caused SARS and Middle East respiratory syndrome (MERS), respectively. Like the SARS-CoV-2 virus, these viruses are thought to originate in bats, but may have had an intermediate mammalian host prior to transfer to humans.


SARS-CoV-2 genetics

Phylogenetic (evolutionary) analysis has helped to establish that SARS-CoV-2 emerged in the human population in November 2019. Since then, continued observation of the genome has identified small mutations that can be used to track the evolution of the virus. The rate of mutation observed for SARS-CoV-2 is significantly lower than influenza, suggesting it is evolving more slowly in response to selective pressure.1,2 Further observation is needed to understand how mutations affect the function of the virus. At the beginning of the pandemic, one variant of the SARS-CoV-2 virus was the most prevalent (D614). In February 2020, a new variant, G614, emerged in Europe and has since replaced D614 as the most dominant form.3  Infection with the G614 variant potentially results in higher viral loads, which has been suggested could influence transmissibility3;  however, this has yet to be fully evaluated. It does not appear that the G614 variant result in greater disease severity.4  Continued study of the genome and relating genomic variants to health and epidemiological data is important to evaluating how the evolution of the virus may impact on the public health response, vaccine development and the design of therapies.1,4


What are the symptoms?

COVID-19 can result in a broad range of symptoms that can vary from person to person. These can include cough, fever, shortness of breath, tiredness, sore throat, body aches, chills, headache and in some cases result in lethal pneumonia. Some people may also experience loss of smell or taste, nausea, vomiting or diarrhea. Among children, abdominal symptoms and skin changes or rash may be more commonly reported.5

The severity of disease can also vary from person to person. Not everyone with COVID-19 will display symptoms, and many cases will only experience mild symptoms.6 About 15% of those experiencing symptoms will require hospitalization, of which about one-third may require admission to intensive care.6 The elderly, the obese, smokers, and immunosuppressed persons and those with pre-existing conditions including diabetes, hypertension, heart disease or cancer are at the greatest risk of requiring hospitalization or dying from COVID-19.7-9

The case fatality rate for COVID-19 differs around the world and across Canada and relates in part to case identification and to local epidemiology.10,11 The case fatality rate for Canada as of July 12, 2020 was reported as 8.2%, with the highest case fatality rates recorded in Quebec (10%), Ontario (7.5%), B.C. (6.2%) and Nova Scotia (5.9%) and no deaths recorded in P.E.I. or the Territories.10 COVID-19 is less prevalent in children as compared to adults, making up only about 1-10% of cases, and children infected with SARS-CoV-2 experience less severe symptoms.12-16 Children under one year of age and with underlying conditions may experience more severe illness than other children, but case mortality rate for children is much lower than for adults.15 Some children with suspected or confirmed COVID-19 have been reported to experience symptoms similar to Kawasaki disease, although this is rare and typically non-life-threatening.17-20


Rate of Transmission

The basic reproduction number for a contagious disease, or the R0 value, estimated at the beginning of an outbreak, indicates the number of secondary cases that can be infected by a primary case in a population with no underlying immunity, vaccine or preventive measures. Where R0 is greater than 1, the number of infected persons is likely to increase. Over time, the effective reproductive number (Rt) changes as more people are infected and public health measures are implemented to contain the spread. The goal of public health interventions is to bring the Rt below 1, which would indicate that the outbreak is reducing and will eventually die out.21 Monitoring the change in Rt can help to evaluate the effectiveness of public health measures.

For SARS-CoV-2 the preliminary World Health Organization estimate of R0 was 1.4-2.522 with subsequent research estimating the mean R0 at 3.28.23 This suggests that every primary case at the beginning of the outbreak could potentially infect about three others. The Rt is an average and can vary depending on the location and patterns of local transmission over time.24   Estimates of Rt can not easily account for secondary cases that are asymptomatic unless these cases have been detected in the population through widespread testing.25  The Rt for Canada near the beginning of the pandemic in March 2020 was estimated to be > 2. Following widespread public health measures to prevent transmission, the Rt dropped to < 1 from about the end of April to late June 2020.26 Since then, the Rt has shown a slight upward trend, reflecting localized outbreaks in some regions of the country. The Rt varies between and within provinces and territories. For example, modelling for the province of Ontario towards the end of June 2020 estimated the median Rt for the province to be 1.0. The Rt was found to vary within Ontario from 0.8 in Toronto to 2.1 in the Northern region.27 This difference is partially explained by the large difference in the total number of cases in Toronto (12802) compared to the Northern region (330).


How is the virus transmitted?

SARS-CoV-2 is primarily transmitted via prolonged close contact with an infected person, likely due to their respiratory secretions passed in the air, which can include a range of droplet sizes, and potentially due to transmission via surfaces (fomites). The vast majority of COVID-19 outbreaks have taken place indoors and are most often associated with close contacts in the home environment, or other indoor spaces where there is a high density of people and an extended period of contact.28-31 


Large respiratory droplets

The primary mode of human-to-human transmission of SARS-CoV-2 is considered to be via direct contact with an infected person and their respiratory droplets generated during coughing, sneezing, and other respiratory actions that produce large droplets (e.g., > 5 µm diameter).32 Exposure potential is greatest in close proximity of an infected person. Large respiratory droplets can be contained by actions such as mask wearing, respiratory etiquette (covering one’s mouth and nose when coughing or sneezing) and via physical distancing measures that help to ensure there is sufficient distance for respiratory droplets emitted from an infected person to drop to the ground before reaching others. Large droplets are thought to travel less than 1 m before dropping to the ground, leading to the 2 m physical distancing practice that has been adopted for limiting the spread in the general public.32-35 Current evidence has shown that measures to protect against the spread of respiratory droplets, namely physical distancing and mask wearing, have led to a reduction in cases.36


Small respiratory droplets/respiratory aerosols

Increasingly, transmission via smaller droplets or respiratory aerosols (< 5 µm diameter) produced by speaking, singing, shouting, or heavy breathing is considered to be an important route of transmission, with some experts calling for greater awareness of airborne precautions for some activities and in some settings.37-43   Small respiratory droplets can remain in the air longer than large droplets and could present both a risk of exposure in close contact with an infected individual, and potentially over longer distances in enclosed spaces.42,44 Some preliminary evidence under experimental conditions suggests that SARS-CoV-2 may remain viable when airborne over short distances for several hours.45,46 Transmission via respiratory aerosols could be occurring in settings where these particles accumulate in poorly ventilated indoor environments where there is a high density of people and extended duration of contact.29,47 Control measures for this type of transmission may rely heavily on reducing crowding, reducing the duration of interactions in indoor spaces, and ensuring good ventilation.48,49

The relative importance of transmission via droplets and airborne aerosols requires further investigation and may have implications for public health recommendations for indoor versus outdoor environments.45,50-54


Contact with surfaces

Contact with contaminated surfaces (fomites) followed by touching of the eyes, mouth or nose is a another possible mode of SARS-CoV-2 transmission, although is not considered to be the main transmission route.32 Fomites can become contaminated by deposition of droplets, aerosols, sputum or feces, either directly or by cross-contamination by touching an object with contaminated hands.

The risk of transmission through contact can depend on the concentration of viable virus, its viability on a specific surface over time (see below for persistence on different surfaces) and the quantity of virus a person is exposed to by touching of the eyes, mouth or nose. Surfaces that are frequently touched by many people, such as door handles or faucets may be more important in fomite transmission compared to objects or surfaces that are only touched incidentally and less frequently. Hand hygiene and routine cleaning and disinfection of surfaces reduces the likelihood of contact transmission.55

There have been few studies that have assessed the presence of viable virus on surfaces. One observations study of surfaces in clinical and public areas of a hospital treating COVID-19 patients found SARS-CoV-2 RNA on over half of the surfaces tested, especially computer keyboards, chairs and alcohol gel dispensers.56 While no culturable virus was detected in the study, evidence of surface contamination supports recommendations for hand and surface hygiene. Washing with soap for 20 seconds followed by rinsing can help to emulsify the lipid layer of the virus, rendering it inviable and diffuse virus particles,  making spread less likely.24,57 Using hand sanitizers to inactivate the virus is an alternative to handwashing.58 Chemical disinfectants can be used to inactivate the virus on surfaces. Both Health Canada59 and the US EPA60 have issued a list of disinfectants that are approved for use on hard surfaces against SARS-CoV-2. The Public Health Agency of Canada (PHAC) has also developed guidance on cleaning and disinfection of public spaces for SARS-CoV-2.61


Transmission via feces

There is some evidence that the SARS-CoV-2 virus is shed via feces,62 and the virus has been detected in the toilets of COVID-19 patients.52-54 Several studies have identified the presence of SARS-CoV-2 RNA in feces but only a few have identified infectious virus.63 There is little evidence to suggest that the fecal-oral pathway (e.g., passing in fecal particles from one person to the mouth, or fecal contamination of food) is significant in the current pandemic.


When is the virus transmitted?

The mean incubation period (time between exposure to the virus and the appearance of symptoms) has been estimated to be around five days,64,65 with modelling indicating a range of about two to 11 days (2.5th and 97.5th percentiles).66,67 An infected person can transmit the virus to others both before they show any symptoms (pre-symptomatic) and when they are symptomatic. The efficiency of viral transmission during exposure can be affected by the number of infectious viral particles inhaled and the duration of exposure for a secondary case.68 Infection may occur as a result of a short but intense dose of infectious virus, or following prolonged exposure to a smaller dose. Current evidence suggests that most transmission occurs during the symptomatic phase, but research is still needed to understand the relative importance of pre-symptomatic and asymptomatic transmission.69


Pre-symptomatic and asymptomatic transmission

The occurrence of pre-symptomatic transmission (during the incubation phase of an infected person) and asymptomatic transmission (transmission via an infected person who never displays symptoms) has been recorded throughout the pandemic in various locations around the world.30,70-74 The precise incidence of pre-symptomatic and asymptomatic transmission and overall importance to the spread of the virus is still unknown. A review of studies by Heneghan et al. (2020) found that between 5% and 80% of people infected with SARS-CoV-2 may be asymptomatic, but the rate of transmission to others requires further study.75

Pre-symptomatic and asymptomatic cases have been found to shed virus.76,77 It is not clear what level of infectious virus is shed during the pre-symptomatic phase, or via asymptomatic spreaders, given that a primary route of transmission (large respiratory droplets) is limited by the absence of coughing and sneezing.72 Other routes of transmission, such as via smaller respiratory droplets released during breathing, speaking, laughing or singing, may be more important for pre-symptomatic or asymptomatic transmission.78 He et al. (2020)79 estimated that infected persons could be transmitting the virus 0.6-2.5 days before the onset of symptoms, although for asymptomatic spread, the period of transmission is still being investigated. Current evidence suggests that asymptomatic transmission is more likely to occur following prolonged close contact, such as in family settings where there may be exposure during shared meals, talking, and contact with shared common objects and surfaces.30,69,74,80


Symptomatic transmission

Once a person becomes symptomatic, they could be transmitting the virus to others for days to several weeks after symptom onset.67 Research is ongoing to help explain the relationship between viral dose (e.g., the level of exposure to the virus via respiratory droplets, or contact with fomites), the viral load (the quantity of viral particles per unit of bodily fluid in the infected person) and severity of disease.81 The viral dose required to cause infection by various routes remains unknown.82 Most cases of COVID-19 are diagnosed using reverse transcription PCR (RT-PCR), which identifies whether viral RNA is present or not, and can provide some indication of the level of viral load.83 While this type of test cannot determine if viral particles are infectious, the more viral RNA in the body may be an indication that more virus can potentially be released by coughs, sneezes, breathing or talking.

The level of viral RNA has been measured to be highest soon after symptom onset in the early stages of the disease, when level of transmission may also be highest, and decreases about one week following the peak.84,85 The virus replicates predominantly in the tissues of the upper respiratory tract.86 The pattern of viral shedding for SARS-CoV-2 has been found to be more similar to influenza as compared to SARS-CoV-1.69,77 Patients with a higher viral load appear to experience more severe symptoms and shed more virus over a longer timeframe than mild cases.87 Positive results for viral RNA do not always indicate that infectious virus is being shed but Woelfel et al. (2020) found that viable virus could be isolated at the peak of viral shedding, about four days after symptom onset.86 Studies of viral load indicate that the amount of viable virus decreases over a much shorter period as compared to viral RNA, which can persist much longer but is not infectious.67


Sensitivity of SARS-CoV-2 to environmental factors

Research is ongoing to understand the persistence of SARS-CoV-2 on different surfaces and under various environmental conditions.


Temperature: Experiments have found that high temperatures are more effective for deactivating the SARS-CoV-2 virus, and the virus is more persistent at colder temperatures. Experiments using viral suspension found minimal reduction over 14 days at 4°C, but detected no viable particles after four days at 22°C, within one day at 37° C, less than 30 minutes at 56°C and less than five minutes at 70°C.88-90 A study of persistence of SARS-CoV-2 in milk also found that pasteurization temperatures of 56°C and 63°C for 30 minutes resulted in no viable virus; however no reduction was detected after 48 hours stored at 4°C, and only a minimal reduction after 48 hours stored at -30°C.91


Humidity: Humidity can influence both persistence on surfaces and infectivity of the virus, by affecting spread of the virus and susceptibility of respiratory systems to viral infection.92 There is preliminary evidence that persistence of the virus may decrease with increases in temperature and humidity and the virus may remain infectious under dry conditions.89,92,93 Further research is needed to better characterise how humidity influences persistence and infectivity of SARS-CoV-2 in indoor and outdoor environments.


Light/Ultraviolet (UV) radiation: UV irradiation has been shown to reduce viral loads for respiratory viruses, including  SARS-CoV-1 in clinical and other controlled settings,94,95 Germicidal effects can occur between 200-320 nm, which covers the range of UV produced by natural sunlight (UV-B, 280-320 nm) and UV produced by lamps for specific applications (UV-C, below 280 nm) Solar UV-B has been shown to provide a disinfectant effect under a high UV-index over a sustained period.96 Disinfection using UV-C is more efficient than UV-B, and UV-C has been shown to be effective for inactivation of double-stranded, enveloped RNA viruses.97-100 UV irradiation has also been proposed as a decontamination method for personal protective equipment (PPE) contaminated by SARS-CoV-2.101-103 Initial results suggest that UV treatment may be more effective on smooth surfaces such as steel as compared to fabrics or porous materials.104 The use of UV-C for disinfection carries some risk, as UV-C can be harmful to human skin and eyes. Further study is needed to determine the optimum dose needed for inactivation of SARS-CoV-2, and how UV-C could be safely applied in public settings.


Persistence on surfaces

A limited number of studies have specifically examined the persistence of SARS-CoV-2 on common surfaces.46,88,105-107 Previous study of coronaviruses (MERS, SARS-CoV-1 and other human coronavirus variants) found that they are detectable on wood, glass, metal and plastic for between four and nine days.106 One of the first studies on SARS-CoV-2 by van Doremalen et al. (2020) found that the virus was most persistent on stainless steel and plastic surfaces and least persistent on cardboard and copper.46 Chin et al. (2020) also found that SARS-CoV-2 was more persistent on smooth, hard surfaces (stainless steel and plastic) than porous materials (wood, cloth, paper and tissue).88 Liu et al (2020) also found that the virus was least persistent on cloth and paper but on most other surfaces, infectious virus was detectable after seven days.108 Studies of persistence on metals such as copper and aluminum have found the shortest level of persistence under experimental conditions.88,107 It is important to note that the studies mentioned have been conducted under different experimental conditions, including temperature, relative humidity, and with variations in the concentrations and volumes of infectious titer that were used. The findings of these studies are presented Table 1 below, however additional research is needed to better understand how experimental conditions relate to real-world situations.


Table 1:  Persistence of SARS-CoV-2 on various surfaces under experimental conditions*


Persistence of SARS-CoV-2 under experimental conditions



Cardboard: up to 24 hours46

Paper and tissue: up to three hours88

Paper: rapid loss of infectivity after one hour; no infectious virus after five days108

Stainless steel

Up to three days (72 hours) although viability significantly reduced at 48 hours46

Up to four days (96 hours)88

> 7 days108


Up to four hours46


Up to four hours107


Up to three days (72 hours)46

Up to four days (96 hours)88

> 92 hours (less than 1 log10 drop on polystyrene after 92 hours)107

> 7 days108


Up to two days88

> 7 days108


Up to four days88

> 44 hours (3.5 log10 drop after 44 hours)107

> 7 days108


> 7 days108


Up to two days88

Cotton: rapid loss of infectivity after one hour; no infectious virus after four days108

Latex gloves

> 7 days108

Surgical mask

> 7 days108


Experimental temperature

Relative humidity

Concentration of infectious titer

Volume of infectious titer

46van Doremalen et al.

21-23 °C

40 %

105 TCID50 per ml

50 µl

88Chin et al.

22 °C

65 %

107.8 TCID50 per ml

5 µl

107Pastorino et al.

19-21 °C

45-55 %

106 TCID50 per ml

50 µl

108Liu et al.

25-27 °C

35 %

106 TCID50 per ml

50 µl

Additional COVID-19 related resources to support environmental health can be found on our Environmental Health Resources for the COVID-19 Pandemic topic page.



  1. Day T, Gandon S, Lion S, Otto SP. On the evolutionary epidemiology of SARS-CoV-2. Curr Biol. 2020; Pre-proof. Available from:
  2. Johns Hopkins University and Medicine. SARS-CoV-2 genetics. Baltimore, MD: Johns Hopkins University and Medicine; 2020 Apr 16. Available from:
  3. Korber B, Fischer WM, Gnanakaran S, Yoon H, Theiler J, Abfalterer W, et al. Tracking changes in SARS-CoV-2 spike: evidence that D614G increases infectivity of the COVID-19 virus. Cell. 2020 Jul 3. Available from:
  4. Grubaugh ND, Hanage WP, Rasmussen AL. Making sense of mutation: what D614G means for the COVID-19 pandemic remains unclear. Cell. 2020 Jul 3. Available from:
  5. Public Health Agency of Canada. Coronavirus disease (COVID-19): symptoms and treatment. Ottawa, ON: PHAC; 2020 [updated Jul 28]; Available from:
  6. CanCOVID network, Tannenbaum C, Sheppard D. Covid symptoms and disease. CanCOVID State of the science report: Volume 2. ON: CanCOVID; 2020. Available from:
  7. Engin AB, Engin ED, Engin A. Two important controversial risk factors in SARS-CoV-2 infection: obesity and smoking. Environ Toxicol Pharmacol. 2020 Aug;78:103411. Available from:
  8. Ho FK, Celis-Morales CA, Gray SR, Katikireddi SV, Niedzwiedz CL, Hastie C, et al. Modifiable and non-modifiable risk factors for COVID-19: results from UK Biobank. medRxiv. 2020 May 2; Pre-print. Available from:
  9. Jordan RE, Adab P. Who is most likely to be infected with SARS-CoV-2? Lancet Infect Dis. 2020 May 15. Available from:
  10. Public Health Agency of Canada. COVID-19 Daily epidemiology update. Ottawa, ON: PHAC; 2020 [updated Jul 27]; Available from:
  11. Public Health Ontario. Review of “Case-fatality rate and characteristics of patients dying in relation to COVID-19 in Italy". Toronto, ON: Queen's Printer for Ontario; 2020 Mar 25. Available from:
  12. Liguoro I, Pilotto C, Bonanni M, Ferrari ME, Pusiol A, Nocerino A, et al. SARS-COV-2 infection in children and newborns: a systematic review. Eur J Pediatr. 2020 Jul;179(7). Available from:
  13. Ludvigsson JF. Systematic review of COVID-19 in children shows milder cases and a better prognosis than adults. Acta Paediatr. 2020;109(6):1088-95. Available from:
  14. Public Health Ontario. COVID-19 - what we know so far about... infection in children. Toronto, ON: Queen's Printer for Ontario; 2020 May 15. Available from:
  15. Shekerdemian LS, Mahmood NR, Wolfe KK, Riggs BJ, Ross CE, McKiernan CA, et al. Characteristics and outcomes of children with coronavirus disease 2019 (COVID-19) infection admitted to US and Canadian pediatric intensive care units. JAMA Pediatrics. 2020 May 11. Available from:
  16. Stringhini S, Wisniak A, Piumatti G, Azman AS, Lauer SA, Baysson H, et al. Seroprevalence of anti-SARS-CoV-2 IgG antibodies in Geneva, Switzerland (SEROCoV-POP): a population-based study. The Lancet. 2020 Jun 11. Available from:
  17. Labé P, Ly A, Sin C, Nasser M, Chapelon‐Fromont E, Saïd PB, et al. Erythema multiforme and Kawasaki disease associated with COVID-19 infection in children. J Eur Acad Dermatol Venereol. 2020 May 26. Available from:
  18. Licciardi F, Pruccoli G, Denina M, Parodi E, Taglietto M, Rosati S, et al. SARS-CoV-2-induced Kawasaki-like hyperinflammatory syndrome: a novel COVID phenotype in children. Pediatrics. 2020 Jul;146(1). Available from:
  19. Public Health Ontario. COVID-19 – what we know so far about...Kawasaki disease-like illness. Toronto, ON: Queen's Printer for Ontario; 2020 May 30. Available from:
  20. Verdoni L, Mazza A, Gervasoni A, Martelli L, Ruggeri M, Ciuffreda M, et al. An outbreak of severe Kawasaki-like disease at the Italian epicentre of the SARS-CoV-2 epidemic: an observational cohort study. The Lancet. 2020 Jun 6;395(10239):P1771-8. Available from:
  21. Inglesby TV. Public health measures and the reproduction number of SARS-CoV-2. JAMA. 2020;323(21):2186-7. Available from:
  22. World Health Organization. Statement on the meeting of the International Health Regulations (2005) Emergency Committee regarding the outbreak of novel coronavirus (2019-nCoV). Geneva, Switzerland: WHO; 2020 Jan 23. Available from:
  23. Liu Y, Gayle AA, Wilder-Smith A, Rocklöv J. The reproductive number of COVID-19 is higher compared to SARS coronavirus. J Travel Med. 2020;27(2). Available from:
  24. Elias B, Bar-Yam Y. Could air filtration reduce COVID-19 severity and spread? Cambridge, MA: New England Complex Systems Institute; 2020 Mar 9. Available from:
  25. Chisholm RH, Campbell PT, Wu Y, Tong SYC, McVernon J, Geard N. Implications of asymptomatic carriers for infectious disease transmission and control. Royal Soc Open Sci. 2018;5(2). Available from:
  26. Public Health Agency of Canada. Update on COVID-19 in Canada: epidemiology and modelling. Ottawa, ON: PHAC; 2020 Jul 28. Available from:
  27. Public Health Ontario. Evolution of COVID-19 case growth in Ontario. Toronto, ON: Queen's Printer for Ontario; 2020 Jun 24. Available from:
  28. Dietz L, Horve PF, Coil DA, Fretz M, Eisen JA, Van Den Wymelenberg K. 2019 Novel Coronavirus (COVID-19) pandemic: built environment considerations to reduce transmission. Msystems. 2020;5(2). Available from:
  29. Furuse Y, Sando E, Tsuchiya N, Miyahara R, Yasuda I, Ko YK, et al. Clusters of coronavirus disease in communities, Japan, January-April 2020. Emerg Infect Dis. 2020 Jun 10;26(9). Available from:
  30. Qian G, Yang N, Ma AHY, Wang L, Li G, Chen X, et al. COVID-19 transmission within a family cluster by presymptomatic carriers in China. Clin Infect Dis. 2020 Aug;71(15). Available from:
  31. Leclerc QJ, Fuller NM, Knight LE, Group CC-W, Funk S, Knight GM. What settings have been linked to SARS-CoV-2 transmission clusters? Wellcome Open Research. 2020 Jun 5;5:83. Available from:
  32. World Health Organization. Modes of transmission of virus causing COVID-19: implications for IPC precaution recommendations. Scientific brief. Geneva, Switzerland: WHO; 2020 Mar 29. Available from:
  33. Atkinson J, Chartier Y, Pessoa-Silva CL, Jensen P, Li Y, Seto W-H. Annex C. Respiratory droplets. Geneva, Switzerland: World Health Organization; 2009. Available from:
  34. National Academies of Sciences Engineering and Medicine. Rapid expert consultation on social distancing for the COVID-19 pandemic. Washington, DC: The National Academies Press; 2020 Mar 19. Available from:
  35. Public Health Agency of Canada. Physical distancing: how to slow the spread of COVID-19. Ottawa, ON: PHAC; 2020 Apr 9. Available from:
  36. Chu DK, Akl EA, Duda S, Solo K, Yaacoub S, Schünemann HJ, et al. Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis. The Lancet. 2020;395(10242):1973-87. Available from:
  37. Anderson EL, Turnham P, Griffin JR, Clarke CC. Consideration of the aerosol transmission for COVID-19 and public health. Risk Anal. 2020;40(5):902-7. Available from:
  38. Anfinrud P, Bax CE, Stadnytskyi V, Bax A. Could SARS-CoV-2 be transmitted via speech droplets? medRxiv. 2020 Apr 6; Pre-print. Available from:
  39. Banik RK, Ulrich AK. Evidence of short-range aerosol transmission of SARS-CoV-2 and call for universal airborne precautions for anesthesiologists during the COVID-19 pandemic. Anesth Analg. 2020 Aug;131(2):e102-e4. Available from:
  40. Buonanno G, Stabile L, Morawska L. Estimation of airborne viral emission: quanta emission rate of SARS-CoV-2 for infection risk assessment. Environ Int. 2020;141:105794. Available from:
  41. Miller SL, Nazaroff WW, Jimenez JL, Boerstra A, Buonanno G, Dancer SJ, et al. Transmission of SARS-CoV-2 by inhalation of respiratory aerosol in the Skagit Valley Chorale superspreading event. medRxiv. 2020 Jun 18; Pre-print. Available from:
  42. Morawska L, Cao J. Airborne transmission of SARS-CoV-2: the world should face the reality. Environ Int. 2020 Apr 10;139:105730. Available from:
  43. Stadnytskyi V, Bax CE, Bax A, Anfinrud P. The airborne lifetime of small speech droplets and their potential importance in SARS-CoV-2 transmission. Proc Nat Acad Sci USA. 2020 Jun;117(22):11875-7. Available from:
  44. Liu L, Li Y, Nielsen PV, Wei J, Jensen RL. Short-range airborne transmission of expiratory droplets between two people. Indoor Air. 2017;27(2):452-62. Available from:
  45. Fears AC, Klimstra WB, Duprex P, Hartman A, Weaver SC, Plante KS, et al. Persistence of severe acute respiratory syndrome coronavirus 2 in aerosol suspensions. Emerg Infect Dis. 2020 Sep;29(9). Available from:
  46. van Doremalen N, Bushmaker T, Morris DH, Holbrook MG, Gamble A, Williamson BN, et al. Aerosol and surface stability of SARS-CoV-2 as Compared with SARS-CoV-1. N Engl J Med. 2020;382:1564-7. Available from:
  47. Qian H, Miao T, Liu L, Zheng X, Luo D, Li Y. Indoor transmission of SARS-CoV-2. medRxiv. 2020 Apr 7; Pre-print. Available from:
  48. British Columbia Centre for Disease Control, British Columbia Ministry of Health. Tools and strategies for safer operations during the COVID-19 pandemic. Vancouver, BC: BC Centre for Disease Control and the BC Ministry of Health; 2020 Jul. Available from:
  49. Institut national de santé publique. COVID-19: Indoor environment. Montreal, QC: INSPQ; 2020. Available from:
  50. Bourouiba L. Turbulent gas clouds and respiratory pathogen emissions: potential implications for reducing transmission of COVID-19. JAMA. 2020;323(18):1837-8. Available from:
  51. Gorbunov B. Aerosol particles laden with COVID-19 travel over 30m distance. Preprints. 2020 Apr 30. Available from:
  52. Ong SWX, Tan YK, Chia PY, Lee TH, Ng OT, Wong MSY, et al. Air, surface environmental, and personal protective equipment contamination by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from a symptomatic patient. JAMA. 2020 Mar 4;323(16):1610-2. Available from:
  53. Santarpia JL, Rivera DN, Herrera V, Morwitzer MJ, Creager H, Santarpia GW, et al. Transmission potential of SARS-CoV-2 in viral shedding observed at the University of Nebraska Medical Center. medRxiv. 2020 Mar 26; Pre-print. Available from:
  54. Liu Y, Ning Z, Chen Y, Guo M, Liu Y, Gali NK, et al. Aerodynamic analysis of SARS-CoV-2 in two Wuhan hospitals. Nature (London). 2020;582(7813):557-60. Available from:
  55. Boyce JM, Pittet D. Guideline for hand hygiene in health-care settings. Recommendations of the Healthcare Infection Control Practices Advisory Committee and the HICPAC/SHEA/APIC/IDSA Hand Hygiene Task Force. MMWR Morb Mortal Wkly Rep. 2002 Oct 25(51(RR16)):1-44. Available from:
  56. Zhou J, Otter JA, Price JR, Cimpeanu C, Garcia DM, Kinross J, et al. Investigating SARS-CoV-2 surface and air contamination in an acute healthcare setting during the peak of the COVID-19 pandemic in London. Clin Infect Dis. 2020 Jun 2. Available from:
  57. US Centers for Disease Control. Handwashing: clean hands save lives. How to wash your hands. Atlanta, GA: US Department of Health and Human Services; 2020 [updated Mar 4]; Available from:
  58. US Centers for Disease Control. Handwashing: clean hands save lives. When & how to use hand sanitizer in community settings. Atlanta, GA: US Department of Health and Human Services; 2020 [updated Mar 3]; Available from:
  59. Health Canada. Hard surface disinfectants and hand sanitizers: list of hard-surface disinfectants for use against coronavirus (COVID-19). Ottawa, ON: Health Canada; 2020 [updated Jul 24]; Available from:
  60. US Environmental Protection Agency. List N: disinfectants for use against SARS-CoV-2 | Pesticide registration. Washington, DC: US EPA; 2020 [updated Mar 26]; Available from:
  61. Public Health Agency of Canada. Cleaning and disinfecting public spaces during COVID-19. guidance. Ottawa, ON: PHAC; 2020 May 29. Available from:
  62. Xiao F, Tang M, Zheng X, Liu Y, Li X, Shan H. Evidence for gastrointestinal infection of SARS-CoV-2. Gastroenterology. 2020;158(6):1831-3. Available from:
  63. Hindson J. COVID-19: faecal–oral transmission? Nat Rev Gastroenterol Hepatol. 2020 Mar 25;17(5):259. Available from:
  64. Lauer SA, Grantz KH, Bi Q, Jones FK, Zheng Q, Meredith HR, et al. The incubation period of coronavirus disease 2019 (COVID-19) from publicly reported confirmed cases: estimation and application. Ann Intern Med. 2020 Mar 10;172(9):577-82. Available from:
  65. Public Health Ontario. COVID-19 – what we know so far about… the incubation period Toronto, ON: Queen's Printer for Ontario; 2020 Feb 3. Available from:
  66. Backer JA, Klinkenberg D, Wallinga J. Incubation period of 2019 novel coronavirus (2019-nCoV) infections among travellers from Wuhan, China, 20–28 January 2020. Eurosurveillance. 2020;25(5). Available from:
  67. Public Health Ontario. COVID-19 – what we know so far about… the period of communicability Toronto, ON: Queen's Printer for Ontario; 2020 Mar 30. Available from:
  68. CanCOVID network, Tannenbaum C, Sheppard D. Viral transmission. CanCOVID State of the science report: Volume 3. ON: CanCOVID; 2020. Available from:
  69. Alberta Health Services. COVID-19 Scientific Advisory Group rapid response report. Key research question: What is the evidence supporting the possibility of asymptomatic transmission of SARS-CoV-2? Edmonton, AB: Government of Alberta; 2020 Apr 13. Available from:
  70. European Centre for Disease Prevention and Control. Transmission of COVID-19. Stockholm, Sweden: ECDC; 2020. Available from:
  71. Health Information and Quality Authority. Evidence summary for asymptomatic transmission of COVID-19 (21 April 2020). Dublin, Ireland: Health Information and Quality Authority; 2020.
  72. Kimball A, Hatfield KM, Arons M, James A, Taylor J, Spicer K, et al. Asymptomatic and presymptomatic SARS-CoV-2 infections in residents of a long-term care skilled nursing facility — King County, Washington, March 2020. MMWR Morb Mortal Wkly Rep. 2020 Apr 3;69:377-81. Available from:
  73. Public Health Ontario. COVID-19 – what we know so far about… asymptomatic infection and asymptomatic transmission. Toronto, ON: Queen's Printer for Ontario; 2020 May 22. Available from:
  74. Wei WE, Li Z, Chiew CJ, Yong SE, Toh MP, Lee VJ. Presymptomatic transmission of SARS-CoV-2 - Singapore, January 23-March 16, 2020. MMWR Morb Mortal Wkly Rep. 2020 Apr 10;69(14):411-5. Available from:
  75. Heneghan C, Brassey J, Jefferson T. COVID-19: What proportion are asymptomatic? University of Oxford, Centre for Evidence-Based Medicine 2020; Available from:
  76. Li W, Su Y-Y, Zhi S-S, Huang J, Zhuang C-L, Bai W-Z, et al. Viral shedding dynamics in asymptomatic and mildly symptomatic patients infected with SARS-CoV-2. Clin Microbiol Infect. 2020. Available from:
  77. Zou L, Ruan F, Huang M, Liang L, Huang H, Hong Z, et al. SARS-CoV-2 viral load in upper respiratory specimens of infected patients. N Engl J Med. 2020;382(12):1177-9. Available from:
  78. Arav Y, Klausner Z, Fattal E. Understanding the indoor pre-symptomatic transmission mechanism of COVID-19. medRxiv. 2020 May 17; Pre-print. Available from:
  79. He X, Lau EHY, Wu P, Deng X, Wang J, Hao X, et al. Temporal dynamics in viral shedding and transmissibility of COVID-19. Nat Med. 2020 May;26(5):672-5. Available from:
  80. Hu Z, Song C, Xu C, Jin G, Chen Y, Xu X, et al. Clinical characteristics of 24 asymptomatic infections with COVID-19 screened among close contacts in Nanjing, China. Sci China Life Sci. 2020 May 1;63(5):706-11. Available from:
  81. Heneghan C, Brassey J, Jefferson T. SARS-CoV-2 viral load and the severity of COVID-19. Oxford, UK: University of Oxford, Centre for Evidence-Based Medicine, Nuffield Department of Primary Care Health Sciences; 2020 Mar 26. Available from:
  82. US Department of Homeland Security. Master question list for COVID-19 (caused by SARS-CoV-2). Washington, DC: US Departmen tof Homeland Security Science and Technology Directorate; 2020 Jul 23. Available from:
  83. Furukawa NW, Brooks JT, Sobel J. Evidence supporting transmission of Severe Acute Respiratory Syndrome Coronavirus 2 while presymptomatic or asymptomatic. Emerg Infect Dis. 2020;26(7). Available from:
  84. Pan Y, Zhang D, Yang P, Poon LLM, Wang Q. Viral load of SARS-CoV-2 in clinical samples. Lancet Infect Dis. 2020;20(4):411-2. Available from:
  85. To KK-W, Tsang OT-Y, Leung W-S, Tam AR, Wu T-C, Lung DC, et al. Temporal profiles of viral load in posterior oropharyngeal saliva samples and serum antibody responses during infection by SARS-CoV-2: an observational cohort study. Lancet Infect Dis. 2020;20(5):565-74. Available from:
  86. Wölfel R, Corman VM, Guggemos W, Seilmaier M, Zange S, Müller MA, et al. Virological assessment of hospitalized patients with COVID-2019. Nature. 2020 May;581(7809):465-9. Available from:
  87. Liu Y, Yan L-M, Wan L, Xiang T-X, Le A, Liu J-M, et al. Viral dynamics in mild and severe cases of COVID-19. Lancet Infect Dis. 2020(Mar 19). Available from:
  88. Chin AWH, Chu JTS, Perera MRA, Hui KPY, Yen H-L, Chan MCW, et al. Stability of SARS-CoV-2 in different environmental conditions. Lancet Microbe. 2020;1(1):e10. Available from:
  89. National Academies of Sciences Engineering and Medicine. Rapid expert consultation on SARS-CoV-2 survival in relation to temperature and humidity and potential for seasonality for the COVID-19 pandemic (April 7, 2020). Washington, DC: The National Academies Press; 2020. Available from:
  90. Wang T, Lien C, Liu S, Selveraj P. Effective heat inactivation of SARS-CoV-2. medRxiv. 2020 May 5; Pre-print. Available from:
  91. Walker GJ, Clifford V, Bansal N, Stella AO, Turville S, Stelzer-Braid S, et al. SARS-CoV-2 in human milk is inactivated by Holder pasteurization but not cold storage. medRxiv. 2020; Pre-print. Available from:
  92. Moriyama M, Hugentobler WJ, Iwasaki A. Seasonality of respiratory viral infections. Ann Rev Virol. 2020;7(1). Available from:
  93. Rahman A, Hossain G, Singha AC, Islam S, Islam A. A retrospective analysis of influence of environmental/air temperature and relative humidity on SARS-CoV-2 outbreak. Preprints. 2020 Mar 23. Available from:
  94. Duan SM, Zhao XS, Wen RF, Huang JJ, Pi GH, Zhang SX, et al. Stability of SARS coronavirus in human specimens and environment and its sensitivity to heating and UV irradiation. Biomed Environ Sci. 2003 Sep;16(3):246-55. Available from:
  95. International Ultraviolet Association. IUVA Fact sheet on UV disinfection for COVID-19. Chevy Chase, MD: IUVA; 2020 Mar. Available from:
  96. Seyer A, Sanlidag T. Solar ultraviolet radiation sensitivity of SARS-CoV-2. Lancet Microbe. 2020;1(1):e8-e9. Available from:
  97. Kowalski W. Ultraviolet germicidal irradiation handbook. New York, NY: Springer; 2009. Available from:
  98. Blázquez E, Rodríguez C, Ródenas J, Navarro N, Riquelme C, Rosell R, et al. Evaluation of the effectiveness of the SurePure Turbulator ultraviolet-C irradiation equipment on inactivation of different enveloped and non-enveloped viruses inoculated in commercially collected liquid animal plasma. PLoS ONE. 2019;14(2). Available from:
  99. Heßling M, Hönes K, Vatter P, Lingenfelder C. Ultraviolet irradiation doses for coronavirus inactivation – review and analysis of coronavirus photoinactivation studies. GMS Hyg Infect Control. 2020;15. Available from:
  100. Houser KW. Ten facts about UV radiation and COVID-19. LEUKOS. 2020;16(3):177-8. Available from:
  101. Bianco A, Biasin M, Pareschi G, Cavalleri A, Cavatorta C, Fenizia C, et al. UV-C irradiation is highly effective in inactivating and inhibiting SARS-CoV-2 replication. medRxiv. 2020 Jun 23; Pre-print. Available from:
  102. Simmons S, Carrion R, Alfson K, Staples H, Jinadatha C, Jarvis W, et al. Disinfection effect of pulsed xenon ultraviolet irradiation on SARS-CoV-2 and implications for environmental risk of COVID-19 transmission. medRxiv. 2020 May 11; Pre-print. Available from:
  103. US Centers for Disease Control and Prevention. Decontamination and reuse of filtering facepiece respirators. Atlanta, GA: US Department of Health and Human Services; 2020 [updated Apr 30]; Available from:
  104. Fischer R, Morris DH, van Doremalen N, Sarchette S, Matson J, Bushmaker T, et al. Assessment of N95 respirator decontamination and re-use for SARS-CoV-2. Emerg Infect Dis. 2020 Sep;26(9). Available from:
  105. Fiorillo L, Cervino G, Matarese M, D’Amico C, Surace G, Paduano V, et al. COVID-19 surface persistence: a recent data summary and its importance for medical and dental settings. Int J Environ Res Public Health. 2020;17(9):3132. Available from:
  106. Kampf G, Todt D, Pfaender S, Steinmann E. Persistence of coronaviruses on inanimate surfaces and their inactivation with biocidal agents. J Hosp Infect. 2020;104(3):246-51. Available from:
  107. Pastorino B, Touret F, Gilles M, Lamballerie Xd, Charrel R. Prolonged infectivity of SARS-CoV-2 in fomites. Emerg Infect Dis. 2020 Sep;26(9). Available from:
  108. Liu Y, Li T, Deng Y, Liu S, Zhang D, Li H, et al. Stability of SARS-CoV-2 on environmental surfaces and in human excreta. medRxiv. 2020 May 12; Pre-print. Available from:



Last Updated July 15, 2020


ISBN: 978-1-988234-39-7.


To provide feedback on this document, please visit


This document can be cited as: National Collaborating Centre for Environmental Health (NCCEH). An Introduction to SARS-CoV-2. Vancouver, BC: NCCEH. 2020 Jul.


Permission is granted to reproduce this document in whole, but not in part. Production of this document has been made possible through a financial contribution from the Public Health Agency of Canada through the National Collaborating Centre for Environmental Health.

Publication Date Jul 15, 2020
Author Juliette O'Keeffe, Shirra Freeman, Anne-Marie Nicol