COVID-19 Primer: What We Know and What We Don’t Know


3D conceptual art made from a microscope image of coronavirus, known as COVID-19, named for the crown of spikes on its surface. Photo: Joao Paulo Burini/Getty Images

April 7 Update

As the novel coronavirus that causes COVID-19 spreads, what we know and don’t know about the pandemic changes almost daily. The number of confirmed cases is now more than 1,360,000 with 76,370 deaths and 293,743 recoveries.

As of Tuesday morning, Canada had 16,667 confirmed and presumptive cases of COVID-19, in every province and territory except Nunavut. The number of reported deaths in the country is 324 with another two abroad, in Japan and Brazil. More than 336,000 people have been tested for the virus, and 3,616 are reported recovered.

On Monday, Canada’s Chief Public Health Officer, Dr. Theresa Tam conceded that non-medical masks could help prevent a person from spreading the virus to others in places where physical distancing is difficult, like grocery stores and on public transit. She said the “collective scientific understanding” now recognizes that transmission is happening more often from pre-symptomatic and asymptomatic people than originally thought.

It’s “extremely important” that medical masks, including N95’s, continue to be reserved for health care workers and people caring for the sick, Tam noted. And she stressed that wearing a non-medical mask has not been proven to protect the person wearing it, urging continued physical distancing and strict hygiene to prevent the spread of COVID-19. Health Canada recommendations for homemade masks.

On Friday, the US Centers for Disease Control began recommending the use of cloth face coverings in public to help curb the spread of COVID-19.

The number of deaths in the United States related to the respiratory illness has topped 10,000. And with 368,174 reported cases, more than twice that of any other country, the U.S. is the epicentre of the COVID-19 pandemic. In a press briefing Sunday, President Donald Trump said he thinks the next two weeks “are going to be very difficult,” predicting that the country will see its outbreak peak.

In Canada, people are advised to continue staying home as much as possible and practise physical distancing.

A federal Quarantine Act remains in place for all travellers returning to Canada, requiring them to observe a mandatory 14-day self-isolation.

According to the Public Health Agency of Canada, 29 per cent of COVID-19 cases in the country are linked to travel — those either exposed while travelling or exposed to a traveller returning to Canada — while 71 per cent are now attributed to community spread, which means there is no known link to travel or previously confirmed cases.

There needs to be no new cases of COVID-19 reported globally for three consecutive weeks before the pandemic can be declared over.

Here is what we know about the virus so far.

What is it?

COVID-19 is a potentially fatal respiratory illness caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). It is related to the common cold, influenza and Severe Acute Respiratory Syndrome (SARS), an outbreak of which in 2002/03 killed 774 people — including 44 in Toronto and 349 in China. The new, or novel, coronavirus is named for spikes on its surface that resemble a crown, allowing it to attach to cells in the lungs and duplicate. Cases began to appear in late December in the Yangtze River port city of Wuhan, China.

By the end of January, Chinese scientists had sequenced the virus’s genome, which showed it had more in common with two bat-related SARS-like viruses that originated in eastern China in 2018 than it did with SARS and the Middle East Respiratory Syndrome (MERS). The results suggested the virus may have originated in bats but was likely transmitted to another animal, perhaps a scaly mammal called a pangolin, before jumping to humans.

A study published March 17 in the journal Nature Medicine has presented another possibility. Authors say there has been no exact match to SARS-CoV-2, the seventh coronavirus known to infect humans, yet found in animals. They suggest the virus may have evolved to spread human-to-human and make them sick years, or perhaps decades, after it jumped from an animal.

What is the incubation period?

Researchers race to pin down characteristics of novel coronavirus, including the incubation period. It’s said to vary between patients, but 0-14 days represents the current official estimated range with most people developing symptoms 5-6 days after infection. However, the exact figure may still be a moving target with reports of possible outliers where incubation may have taken up to 27 days.

What are the symptoms?

In a review of cases in Canada, PHAC says commonly reported symptoms include cough (78  per cent), chills (51 per cent) and fever (49 per cent).

If you think you’ve been exposed to COVID-19, PHAC has an online self-assessment tool, and people are advised to call their public health authority for what they should do.

In a review of more than 55,000 confirmed cases in China, the WHO reported that signs of COVID-19 ranged from no symptoms (asymptomatic) to severe pneumonia. The most common symptoms recorded were fever (87.9 per cent), dry cough (67.7 per cent), fatigue (38.1 per cent), sputum, or phlegm production (33.4 per cent), shortness of breath (18.6 per cent) and sore throat (13.9 per cent ). Nasal congestion, however, was rare (4.8 per cent).

Loss of taste and smell are also now being reported as possible symptoms.

How does it spread?

Coronaviruses are zoonotic, which means they can pass from animals to humans. Similar to SARS, the novel coronavirus can also pass from human to human, most often through respiratory droplets spread by sneezing and coughing, but also by touching something with the virus on it, then touching your mouth, nose or eyes before washing your hands.

Chinese researchers have reported fecal-oral transmission is also possible, warning medical workers to protect themselves against vomit and feces from infected patients. Chinese health authorities urged vigilance by washing hands frequently, especially if citizens had mildly ill family members at home with them.

Airborne spread is not believed to be a major driver of transmission, according to the WHO.

A study recently published by The New England Journal of Medicine did show that the SARS-CoV-2 virus can survive in the air and on surfaces. Suspended in a fine mist in a lab, the virus remained “viable” and “infectious” for three hours, but authors note that would likely be closer to half an hour under real-world conditions.

The researchers also reported that the virus survived on plastic, for as long as 72 hours; on stainless steel, for as long as 48 hours; on cardboard, for no longer than eight hours; and on copper, for no longer than four hours.

Health Canada notes that coronaviruses are one of the easiest types of viruses to kill with the appropriate disinfectant, and recommends cleaning high-touch surfaces such as door handles often, using either regular household cleaners or diluted bleach.

What is the risk?

Most people, about 80 per cent, infected with COVID-19 have mild to moderate disease and recover on their own. According to statistics reporting site Worldometer, so far more than 270,000 people have fully recovered.

The Public Health Agency of Canada says that there is an increased risk of more severe outcomes for Canadians:

  • aged 65 and over
  • with compromised immune systems
  • with underlying medical conditions

The latest data from PHAC shows that 32 per cent  of cases are in people 60 years of age and older; 35 per cent are 40 to 59; and 33 per cent are 39 and under.

And confirming what was observed early in the outbreak, the WHO report found that individuals at highest risk for severe disease and death include people aged over 60 and those with underlying conditions such as hypertension, diabetes, cardiovascular disease, chronic respiratory disease and cancer.

Dawn Bowdish, the Canada Research Chair in Aging and Immunity, says one of the reasons older people can get sicker is comorbidity, which refers to pre-existing conditions.

“Type 2 diabetes causes your white blood cells to function less effectively. We call it immunometabolism. So there’s a real link between the immune system and the metabolic system, and older adults are at increased risk for Type 2 diabetes or have pre-diabetes.”

Our immune system, which can wane with age, is also a factor.

“Older adults tend to have higher amounts of the virus because they can’t get rid of it as much, and it tends to infiltrate deep into their lungs. Without a really robust immune system, it’s really challenging.”

Her advice for those who have chronic health conditions like Type 2 diabetes is to keep their conditions managed.

“People who have Type 2 diabetes are more likely to be infected. But people who have well-managed disease — they keep their blood sugars stable — are always better off. Similarly, for people who have heart disease, keeping it well managed with exercise and healthy eating, that helps.

“[And] keeping your muscle mass. Because when you’re sick and you can’t eat, that’s what your body uses as energy. So building muscle helps older adults deal with infections. For this particular virus, stay away [from it] is the best advice.”

Should I see the grandkids?

Speaking with Zoomer again, Bowdish expressed concern about potential school closures, now in place across the country, as children are traditionally vectors, or delivery vehicles, for diseases like colds and the flu.

“We still really don’t understand why [children] don’t have (COVID-19) symptoms, but it appears they are infected at the same rates as adults,” she says. “But when schools are closed, who takes care of the kids? The grandparents, right? So that could be problematic, having a grandparent with a pre-existing condition now being the babysitter.”

In a study published near the end of March by The Lancet, findings showed that children are susceptible to SARS-CoV-2 infection, but they frequently do not have notable disease. Authors said that if children are “important in viral transmission and amplification, social and public health policies (eg, avoiding interaction with elderly people) could be established to slow transmission and protect vulnerable populations.”

What is social distancing?

Think of it as physically distancing yourself from others and according to PHAC, social distancing is proven to be one of the most effective ways to reduce the spread of illness during an outbreak. Precautions include:

  • keeping a distance of at least 2 arms length (approximately 2 metres or 6 feet) from others, as much as possible
  • limiting contact with people at higher risk (e.g. older adults and those in poor health)
  • working from home and staying home as much as possible
  • using food delivery services or online shopping

Mask or no mask?

The WHO advices “rational use” of medical masks, stating: “Only wear a mask if you are ill with COVID-19 symptoms (especially coughing) or looking after someone who may have COVID-19. Disposable face mask can only be used once. If you are not ill or looking after someone who is ill then you are wasting a mask.”

PHAC echoes the WHO’s recommendation, with the added warning that: “Wearing a mask when you are not ill may give a false sense of security. There is a potential risk of infection with improper mask use and disposal. They also need to be changed frequently.”

However, the US Centers for Disease Control has begun recommending the use of cloth face coverings in public to help curb the spread of COVID-19.

Wash your hands often and thoroughly — for at least 20 seconds — with soap and water or use a 60 per cent or more alcohol-based sanitizer. It’s not rocket science, but it is the No. 1 piece of advice from health authorities and experts. Coughing and sneezing into your elbow or a tissue, is the second. Part of why physical distancing measures include staying 2 metres (six feet) away from others is because sneezing or coughing can spread respiratory droplets that far.

As for wearing a medical mask or a N95 respirator, Dr. Mark Loeb, a researcher and professor at McMaster University in Hamilton who specializes in pathology, molecular medicine and clinical epidemiology, says health-care workers are the only ones who need to cover up.

“Health-care workers should use some sort of mask, either a medical mask or a N95 respirator if they are performing aerosol-creating procedures, like bronchoscopy or intubation,” said Loeb, who helped with Ontario’s response to SARS 16 years ago and led a study into best practices for reducing transmission rates.

“The evidence [for] people on the street having to wear a mask is zero. General public: total waste.”

Buying up masks just depletes the stock for people who need them.  “Particularly for people who are getting N95 respirators — that’s an extra waste. If you have people walking around Toronto wearing a mask, it doesn’t make sense because the risk is so small.”

Even during SARS, he noted the people who were getting infected were health-care workers directly exposed to patients.

“People walking down Yonge Street were not at risk of getting SARS.”

Bowdish echoes Loeb, while also pointing out that mask quality can make them even less effective.

“The cheap ones that you buy are not as effective as you’d want them to be. Don’t touch your face. Wash your hands. Don’t go anywhere where people are sick. …  don’t go anywhere if you’re sick. Don’t let your friends and family go to work when they’re sick. Those are the best practices. And get your flu shot because in our country, influenza is going to cause more deaths than the coronavirus ever will.”

(Seasonal influenza contributes to more than 3,000 deaths annually in Canada. Globally, it results in about three to five million cases of severe illness, and between 290,000 to 650,000 deaths each year.)


Global Affairs recommends that Canadians avoid non-essential travel outside the country until further notice.

The Canada-U.S. border is closed to all non-essential travel, exceptions are being made for people such as health care workers and truckers.

Canadian citizens and permanent residents are permitted entry by land, sea and air but all other foreign nationals are restricted with exceptions such as diplomats and family returning with Canadians.

Transport Canada rules now restrict people exhibiting symptoms of COVID-19 to board international flights returning to Canada and that has been extended to domestic flights within Canda and trains operating across the country.

All travellers returning to the country are now required to observe a mandatory 14-day quarantine under the federal Quarantine Act. That self-isolation must be done in a place where they do not have contact with vulnerable people, such as older adults and individuals with underlying medical conditions.

Global Affairs is providing up to $5,000 in financial assistance to those living, working or travelling abroad via the COVID-19 Emergency Loan Program. People can call the Emergency Watch and Response Centre in Ottawa at +1 613-996-8885 (collect calls are accepted where available) or email [email protected] to determine eligibility for the expense of retuning to Canada or recovering outside its borders.

Public Health also advices against travelling to, and staying at cottages or summer homes as resources, including health care support for COVID-19, cannot support a surge of need.

Although wearing a medical mask during flights may give you some protection, Loeb says the benefit can be negated as soon as you put your hands under the mask to scratch or eat.

“Wash your hands. That’s the best advice. These viruses are on things, people touch things and then they touch their mouth and noses and eyes. And carry an alcohol-based sanitizer for when you don’t have access to soap and water.”

Highlighting its importance, a study published in the journal Risk Analysis, just before the outbreak began in late December, estimates that improving hand washing rates in just 10 of the world’s leading airports could significantly reduce the spread of many infectious diseases — and authors say that applies to this outbreak as well.

They also estimate that on average, only about 20 per cent of people in airports have clean hands — washed with soap and water, for at least 15 seconds, within the last hour or so. The other 80 per cent are potentially contaminating everything they touch with whatever germs they may be carrying.