Coronavirus is a large family of viruses that can cause illness in humans or illness in animals. Human coronaviruses are quite common and are usually associated with cold-like symptoms. Some rare cases of animal coronaviruses can infect people and be transmitted from one person to another (1).

  1. The SARS-CoV-2 virus and its origins
  2. How is it different from the SARS-CoV-1 virus responsible for the outbreak in 2003?
  3. How is it different from the flu?
  4. How can I get infected with COVID-19?
  5. Who can transmit COVID-19?
  6. Symptoms of COVID-19 and disease evolution
  7. What are some signs and symptoms of a severe infection?
  8. Who’s more at risk?
  9. Are you immunized from COVID-19 once you are recovered?

The SARS-CoV-2 virus and its origins

COVID-19 is a disease associated with infection by the SARS-CoV-2 virus, a virus that had not been previously identified in humans. It is now the seventh coronavirus known to infect humans. The first case of COVID-19 was identified in Wuhan in the Hubei province of China in December 2019. Genome studies suggest that the SARS-CoV-2 virus comes from an animal source, like a lot of other coronaviruses. Similarities between this virus and bat and pangolin viruses suggests that these two animals could have served as reservoir hosts for SARS-CoV-2 (2).

University of Toronto professor Dr. Nick Woolridge created the following video to help others visualize what the SARS-CoV-2 virus particle actually looks like:

Nick Woolridge (https://www.nickwoolridge.xyz/projects/sars-cov-2)

How is it different from the SARS-CoV-1 virus responsible for the outbreak in 2003?

SARS or Severe Acute Respiratory Syndrome is a respiratory illness that is associated with infection by a coronavirus. There are two major coronavirus that have been identified to be the cause of SARS in the past 20 years, the SARS-CoV-1 and SARS-CoV-2 viruses. The SARS-CoV-1 virus was the cause of the worldwide outbreak in 2003, whereas the SARS-CoV-2 virus is associated with the COVID-19 pandemic of 2019-2020. Both viruses seem to have originated from China. The first case of SARS-CoV-1 was reported in the Guangdong province of Southern China whereas the first case of COVID-19 was reported in the Hubei province of Central China. Both viruses seem to have originated from an animal, and it is suggested that the SARS-CoV-1 virus evolved from cave-dwelling horseshoe bats through masked palm civets before infecting humans (21).  

These two coronaviruses share a very similar range of symptoms, from dry cough to severe acute respiratory distress. However, the SARS-CoV-1 virus infection seems to be more deadly, as it is reported to have killed about 1 out of 10 people infected worldwide, as opposed to the approximate 6,9% death rate of COVID-19 reported by the World Health Organisation (WHO). Conversely, the SARS-CoV-2 virus seems to be propagating more rapidly. In fact, there were only 8,098 reported cases of SARD-CoV-1 infection worldwide during the 2003 pandemic, whereas there are 2,544,792 confirmed cases of COVID-19 around the world as of April 23rd (17,18).

How is it different from the flu?

Influenza and COVID-19 are diseases caused by viral infections of the respiratory tract that can vary from asymptomatic or mild disease to severe pneumonia, acute respiratory distress and possibly death (see Symptoms of COVID-19 and disease evolution for more details). Since they can be transmitted in a similar fashion, a lot of the prevention strategies recommended by Public Health are appropriate in both cases. While these diseases share many similarities, we have listed some of the notable differences between both illnesses, as illustrated by data from the World Health Organization (WHO) (5):

  • Influenza actually spreads faster than COVID-19
  • Time between infection and apparition of symptoms is typically shorter in Influenza
  • COVID-19 is estimated to be overall more contagious than Influenza
  • While children are typically important drivers of influenza transmission, it would appear that it is the other way around for COVID-19, where children are mostly infected from adults
  • There is a larger fraction of cases with severe symptoms or critical illness with COVID-19 than with Influenza. People are also 15 times more likely to die from COVID-19 than the flu.

Although these differences are very interesting to note, one important question remains to be answered: how can you tell if you have COVID-19 or the flu? As mentioned before, an individual infected with either of these two viruses can present with very similar symptoms. So how can we differentiate them clinically? Fortunately, the following chart, created by the Alberta Health Services, helps us compare the symptoms of COVID-19 from those of the flu and the common cold (see Symptoms of COVID-19 and disease evolution for more details on the symptoms of COVID-19) (6).

Alberta Health Services


How can I get infected with COVID-19?

After coming in contact with COVID-19, the virus tends to make its way to the nose, throat and lungs and causes an infection in those areas. 

Human coronaviruses are mostly spread from person to person. There have been some rare case reports of pets infected with COVID-19, but present data shows that the risk of pets transmitting COVID-19 to people is pretty low. However, there is a need for more research in that area, and it is recommended that the same protective measures applied between members of the same family be applied to household pets as well (7).

COVID-19 is most commonly known to spread from an infected person to someone else through :

  • Respiratory droplets that spread when you cough, sneeze or talk within 1 meter of another person (9)
  • Close, prolonged personal contact, such as touching or shaking hands
  • Touching something with the virus on it, then touching your mouth, nose or eyes before washing your hands. 
  • Personal items such as cellphones, tablets, glasses, and remote controls and surfaces like doorknobs, toilet seats, tables, window ledges, and floors were shown to be possible sources of COVID-19 contamination (20, 22).

The length of time during which COVID-19 can survive on surfaces depends on the material. The following chart illustrates how long the virus survives on different materials, according to the WHO.

It is important to take note that cleaning counters and surfaces with common household disinfectants will kill the virus. The government of Canada has issued a list of hard-surfaces disinfectant and hand sanitizers that are safe and likely to be effective in eliminating COVID-19. The list can be found here: https://www.canada.ca/en/health-canada/services/drugs-health-products/disinfectants/covid-19/list.html#tbl1

Current evidence suggests person-to-person spread is common when there is close contact. At the moment, there is no evidence to suggest that COVID-19 can be spread through the air, the stool of an infected person or their blood (8).

Who can transmit COVID-19?

Individuals tested positive for COVID-19 can be divided in three different categories : asymptomatic, pre-symptomatic, and symptomatic carriers. Individuals tested positive for COVID-19 can be divided in three different categories : asymptomatic, pre-symptomatic, and symptomatic carriers. By selecting any of the icons on the following chart, you can have access to additional information about that specific type of carrier. Individuals tested positive for COVID-19 can be divided in three different categories : asymptomatic, pre-symptomatic, and symptomatic carriers.

Asymptomatic: There is some evidence that people who are positively tested for COVID-19 can present without any symptoms for the entire course of their infection. Present data is unclear whether they can transmit the virus, and if so, whether they are important drives of the pandemic. There is ongoing research on this topic, and updated findings will be shared on the website when the data is more conclusive. 

Pre-symptomatic: When an individual with COVID-19 is asymptomatic, but will develop symptoms in the following days, he is considered pre-symptomatic. This usually means that the person was recently infected and is still in the incubation period of the disease  (see Symptoms of COVID-19 and disease evolution). There is evidence that shows pre-symptomatic transmission of COVID-19.

Symptomatic: Symptomatic means that an infected individual shows signs or symptoms associated with COVID-19. According to studies, people in this category are the most at risk of transmitting COVID-19. Some preliminary data also suggests that people are generally more contagious in the first few days of symptoms than at the end of the disease (11).

Symptoms of COVID-19 and disease evolution

After coming in contact with COVID-19, people will initially go through a phase called incubation period. The incubation period or latent phase represents the time between infection and symptoms. At that time, the virus is busy replicating itself inside its host’s body, and the affected person will develop symptoms after there is enough virus to cause damage. The typical incubation period for COVID-19 is from 3 to 14 days, but the average period is between 5-6 days (11,12). 

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After the incubation period, people tend to present mild and non-specific symptoms, such as: 

  • Fever
  • Fatigue
  • Dry cough
  • Chills
  • Sore throat
  • Headache
  • Muscle ache
  • Loss of smell or taste
  • Nausea & vomiting
  • Diarrhea

People who are more fragile can develop shortness of breath from the start. In 81% of cases, people will only experience mild to moderate symptoms for the entire length of the disease and recover at home after about 14 days (13). 

For the minority that will evolve into a more severe disease, they will typically develop shortness of breath days after onset of symptoms. It has been observed that older patients with an already impaired lung function typically develop this symptom after about 5-7 days, but it can take longer in young and healthy individuals. This seems to be a major event in the course of the disease, since those people tend to rapidly deteriorate afterwards. In fact, according to studies in China and the US, most people who have developed a severe pneumonia and who have required hospitalization have been admitted on average after about a week of showing symptoms (15,16). 

In some rare cases, the disease can evolve into severe acute respiratory distress, in which case the person will require mechanical ventilation to breathe and will be admitted to the intensive care unit (ICU).

It is important to note that even though COVID-19 can quickly develop into a severe disease, as of April 26th, only 6% of reported cases of COVID-19 in Canada have resulted in death (14). 

The following table offers a short summary of the spectrum of symptom severity of COVID-19, according to the Government of Canada (14).

This chart, created by CBC news, can help you visualize the evolution of COVID-19.

What are some signs and symptoms of a severe infection?

If you show any of the symptoms mentioned before (see Symptoms of COVID-19 and disease evolution) and suspect you might have COVID-19,

If you have any of the following conditions, you are more at risk of severe complications of  COVID-19:

  • Age 65 years or older
  • Heart diseases
  • Lung conditions
  • Kidney disease 
  • High blood pressure
  • Diabetes 
  • Weakened immune system
  • Cancer
  • Obesity

Who’s more at risk?

If you have any of the following conditions, you are more at risk of severe complications of  COVID-19:

  • Age 65 years or older
  • Heart diseases
  • Lung conditions
  • Kidney disease 
  • High blood pressure
  • Diabetes 
  • Weak immune system
  • Cancer
  • Obesity

Are you immunized from COVID-19 once you are recovered?

There is some research suggesting that COVID-19 specific antibodies formed by the immune system following infection may have a protective role from future infection. However, more research needs to be done before in this area. It is also important to note that immunity varies from one individual to another and the factors that play a role in the risk of re-infection haven’t been established yet. In short, it is unclear at the moment whether recovering from COVID-19 infection can lead to immunity (12).

References

  1. Government of Canada [Online]. Coronavirus disease (COVID-19): Symptoms and treatment [updated June 11 2020; cited May 5 2020]. Available from: [link]
  2. Andersen KG, Rambaut A, Lipkin WI, Holmes EC, Garry RF. The proximal origin of SARS-CoV-2. Nature Medicine [Online]. March 17 2020 [cited on May 5 2020]; 26:450-452. Available from: [link]
  3. World Health Organization [Online]. Maladie à coronavirus 2019 (COVID-19) : questions-réponses. 2020 [cited May 5 2020]. Available from: [link]
  4. Centers for Disease Control and Prevention [Online]. Frequently asked questions about SARS [updated May 3 2003; cited May 5 2020]. Available from: [link]
  5. World Health Organization [Online]. Q&A Influenza and COVID-19 – similarities and differences [update March 17 2020; cited May 5 2020]. Available from: [link]
  6. Alberta Health Services [Online]. COVID-19 symptoms in comparison to the flu and the common cold. 2020 [cited May 5 2020]. Available from: [link]
  7. Centers for Disease Control and Prevention [Online]. COVID-19 and Animals [updated June 22 2020; cited May 5 2020]. Available from: [link]
  8. Public Health Ontario [Online]. COVID-19 – What we know so far about… Routes of transmission [updated April 28 2020; cited May 5 2020]. Available from: [link]
  9. Alberta Health Services, COVID-19 Scientific Advisory Group [Online]. Key Research Question: What is the evidence supporting the possibility of asymptomatic transmission of SARS-CoV-2? [updated April 13 2020; cited May 5 2020]. Available from: [link]
  10. Public Health Ontario [Online]. What we know so far about… Asymptomatic Infection and Asymptomatic Transmission [updated May 22 2020; cited May 5 2020]. Available from: [link]
  11. World Health Organization [Online]. Coronavirus disease 2019 (COVID-19) Situation Report – 73 [updated April 2 2020; cited May 5 2020]. Available from: [link]
  12. McIntosh K, Hirsch MS, Bloom A. Coronavirus disease 2019 (COVID-19): Epidemiology, virology and prevention. UpToDate [Online]. [updated June 18 2020; cited May 5 2020]. Available on: [link]
  13. Cascella M, Rajnik M, Cuomo A, Dulebohn SC, Di Napoli R. Features, Evaluation and Treatment Coronavirus (COVID-19). StatPearls Publishing, Treasure Island (FL) [Online]. [updated May 18 2020; cited May 5 2020]. Available on: [link]
  14. Government of Canada [Online]. Coronavirus disease (COVID-19): Outbreak update [updated June 22 2020; cited May 5 2020]. Available on: [link]
  15. Wang D, Hu B, Hu C, et al. Clinical Characteristics of 138 Hospitalized Patients With 2019 Novel Coronavirus-Infected Pneumonia in Wuhan, China. JAMA [Online]. February 7 2020 [cited on May 5 2020]; 323(11):1061-1069. Available from: [link]
  16. Bhatraju PK et al. COVID-19 in Critically Ill patients in the Seattle Region – Case Series. New England Journal of Medicine [Online]. March 30 2020 [cited May 5 2020]; 382:2012-2022. Available from: [link]
  17. World Health Organization [Online]. Coronavirus disease 2019 (COVID-19) Situation Report – 94 [updated April 23 2020; cited May 5 2020]. Available from: [link]
  18. Government of Ontario, Ministry of Long Term-Care. Severe Acute Respiratory Syndrome (SARS). In: Infectious Diseases Protocol [Online]. Ontario (Canada). February 2019 [cited May 5 2020]. Available from: [link]
  19. Harvard Health Publishing [Online]. Coronavirus Resource Center [updated June 23 2020; cited May 5 2020]. Available from: [link]
  20. Guo ZD et al. Aerosol and Surface Distribution of Severe Acute Respiratory Syndrome Coronavirus 2 in Hospital Wards, Wuhan, China, 2020. Emerging Infectious Diseases [Online]. 2020 [cited May 5 2020]; 26(7):1583-1591. Available from: [link]
  21. Cyranoski D. Bat cave solves mystery of deadly SARS virus – and suggests new outbreak could occur. Nature [Online]. December 1 2017 [cited May 5 2020]. Available from: [link]
  22. Santarpia JL et al. Transmission Potential of SARS-CoV-2 in Viral Shedding Observed at the University of Nebraska Medical Center [Online]. March 26 2020 [cited May 5 2020]. Available from: [link]