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

May 22 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 worldwide is 5.23 million, with 335,584 deaths and 2.1 million recoveries.

By Friday morning, Canada had 81,324 confirmed and presumptive cases of COVID-19 in every province and territory but Nunavut. The number of reported deaths is 6,152 and 41,715 people have recovered. A total of 1,379,731 people have been tested for the novel virus.

As many countries continue the way down their epidemic curve, the World Health Organization confirmed this week that we’re still seeing record numbers of new cases globally — the most, more than 107,000, were reported Thursday. Russia and Brazil have now surpassed the U.K., Spain and Italy to sit second and third behind the U.S. with the most known cases of COVID-19.

In Canada, provinces and territories continue to lift lockdown with a varied picture across the country. A travel bubble is being considered by the premiers of New Brunswick, where there had been two weeks without a new case until Thursday, and P.E.I., where there has been no cases reported for more than two weeks. The plan would see residents able to travel between the two provinces without having to self-quarantine for 14 days.

In Ontario, people can now visit retail businesses with street-front entrances and participate in some outdoor activities including golf, tennis and horseback riding. But as the province moves through phase one of its reopening, it was announced this week that schools will remain closed until the fall with Premier Doug Ford saying, “I’m just not going to risk it.” New daily cases have been trending upwards in the province for nearly two weeks with 441 reported on Friday — the highest daily increase since May 8.

Meanwhile, B.C. officials are reopening schools for voluntary and staggered attendance on June 1. New daily cases continue to decline in the province, however, Health Officer Dr. Bonnie Henry remains concerned. “The optimist in me would like to think that maybe it will go away, and the virus will mutate and won’t become worse,” she said Wednesday in an interview with the CBC. “But you know what? We’ve never had a pandemic in recorded history that has not had a second wave.” She has urged residents to stay local through the summer to help curb the spread of the virus.

Based on expert predictions, a group of senators in the United States have urged the White House to prepare for a second wave of infections in the fall when flu season normally begins. The U.S. has the highest number of COVID-19 cases globally followed by Russia, Brazil, Spain, the U.K., Italy and France. By Thursday morning, the country was reporting 1.62 million cases and more than 96,000 deaths. All 50 states are now in some phase of reopening with at least 16 reporting upward trends on the number of new daily cases. A Pew Research Center poll found that 68 per cent of Americans were worried about coronavirus-related restrictions being lifted too quickly.

A joint Canada-U.S. agreement to ban all but essential travel across borders was extended by another month Tuesday, and will remain in place until June 21.

According to the Public Health Agency of Canada, 19 per cent of all COVID-19 cases in the country are linked to travel while 81 per cent are 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 mid-March 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, there have 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 the most commonly reported symptoms include cough (74  per cent), headache (57 per cent) and weakness (55 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 or even laughing but also by touching something with the virus on it, then touching your mouth, nose or eyes before washing your hands.

Chinese researchers reported fecal-oral transmission was 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.

However, 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 2.1 million people have 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 most common reported by Canadians have been cardiac disease, respiratory disease, and diabetes.

Public Health data shows that although about a third (37 per cent) of cases have been in people 60 years of age and older, this age group represents 65 per cent of all reported hospitalizations, 64 per cent of all reported ICU admissions, and 95 per cent of deaths related to COVID-19.

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 60 and over, 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.

Bowdish says inflammation in our body, which increases with age, can also impair immune response.

“People who manage their chronic conditions are really managing their inflammation, and that then helps the immune system do what it needs to do when it comes in contact with a new threat.

“[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.”

Bowdish has since noted that as data surfaces from the epidemic in North America, obesity is being observed as another risk factor for severe illness.

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

What’s the difference between PCR and serological tests?

One of the studies being done by Bowdish’s lab is serology, or the antibody response of people infected with COVID-19.

“Our current tests measure the virus directly by swabbing the back of the sinuses and measuring the amount of viral nucleic acids by PCR [polymerase chain reaction]. It has a low false positive rate when there is little virus, like at the beginning or ending of an infection. Essentially, these can only be used to detect if you are currently sick,” she says.

“[Serological] tests are considered the most reliable measures to figure out how many people have been infected by a virus because they will detect people who’ve been asymptomatic as well as symptomatic.”

Although it’s not yet known how long people might have immunity after being infected, Bowdish says blood tests to detect COVID-19 antibodies could help back-to-work planning, especially for people working in high-risk settings.

Mask or no mask?

The WHO advises “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 has echoed the WHO’s recommendation, while 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 agency now recommends covering the nose and mouth to help prevent spreading the virus in places where physical distancing is difficult, like grocery stores and on public transit. Health Canada recommendations for homemade masks.

PHAC does warn that non-medical masks or facial coverings should not be placed on:

  • children under age 2 (as there could be a choking hazard)
  • anyone who has trouble breathing
  • anyone who is unconscious, incapacitated or otherwise unable to remove the mask without assistance

The US Centers for Disease Control is also 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, coughing and even laughing can spread respiratory droplets that far or farther.

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 ones who need them.

“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.

Buying up medical 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 one, it doesn’t make sense because the risk is so small.”

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.”


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.

A federal Quarantine Act remains in place for all travellers returning to Canada, requiring them to observe a mandatory 14-day self-isolation. Those arriving from abroad now need to present a plan for quarantine that includes food and medication delivery plus assurances that they will not be in a place where a person 65-plus, or with pre-existing health conditions, resides. People who don’t have a plan will be moved to a federally-funded quarantine site, such as a hotel.

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.

And a new rule requirespeople flying within the country to use a non-medical mask covering their nose and mouth in the following situations:

  • at Canadian airport screening checkpoints, where the screeners cannot always keep two metres of separation
  • between themselves and the traveller; when they cannot physically distance from others, or as directed by the airline employees; and
  • when directed to do so by a public health order or public health official.

All travellers returning to the country are 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 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.

Here are some credible sources for up-to-date information.

Public Health Agency of Canada
World Health Organization
Public Health Ontario
B.C. Centre for Disease Control
U.S. Centers for Disease Control 
Johns Hopkins University and Medicine