Coronavirus disease (COVID-19)


NCCID Disease Debriefs provide Canadian public health practitioners and clinicians with up-to-date reviews of essential information on prominent infectious diseases for Canadian public health practice. Information is gathered from key sources including the Public Health Agency of Canada (PHAC), the USA Centers for Disease Control and Prevention (CDC), the World Health Organization (WHO) and the European Centre for Disease Prevention and Control (ECDC).

This Disease Debrief provides quick links for public health and practitioner use.

Information on COVID-19 vaccines is available here:

COVID-19 vaccine: Canadian Immunization Guide

NACI Statements and Recommendations


The Coronavirus disease (COVID-19) is a global pandemic, as announced by World Health Organization (WHO, March 11th, 2020). It is caused by SARS-COV-2 coronavirus, a virus strain never previously identified in humans. The genetic sequence indicates that it is a betacoronavirus, closely linked to the SARS virus. The government of Canada has issued COVID-19 pandemic guidance for the health sector for federal, provincial and territorial health authorities.

For information on SARS-CoV-2 Variants of Concern (VOC), please see NCCID’s VOC summary.

A detailed epidemiologic summary and COVID-19 outbreak update for Canada are available from the Public Health Agency of Canada.

Government of Canada – Coronavirus disease (COVID-19)-For Health Professionals (English and French)

World Health Organization – Coronavirus (COVID-19) (English and French)

European Centre for Disease Prevention and Control: Coronaviruses (English only)

Signs & symptoms

The most commonly observed symptoms of COVID-19 infection are fever, flu, fatigue, new or worsening cough, loss of appetite, loss of smell and/or taste, muscle and body ache, and headache. Gastrointestinal symptoms (abdominal pain, diarrhea, vomiting) can be less frequent. Shortness of breath is commonly reported in hospitalized patients. The symptoms in the geriatric population and in people with underlying health conditions may be subtle or atypical e.g., they could present without fever or respiratory symptoms. Overall, the frequency of symptoms is not well established, and symptoms may develop over time. This virus has an estimated incubation period from 1-14 days, with a median being 5-6 days, from exposure to symptom onset. Most individuals (97.5%) develop symptoms within 11.5 days of exposure. Recent research shows that transmission of the virus can occur from infected persons before they develop symptoms (pre-symptomatic transmission) and from infected persons who never develop symptoms (asymptomatic transmission).

According to the Public Health Agency of Canada: “COVID-19 includes clinical features that present in varying type, frequency, severity and within different age groups. Published reports often over-represent individuals who have more severe symptoms and these may differ across care settings and between different age groups. Symptoms that are absent at the onset of illness may develop over time with disease progression. To date, there is no comprehensive list of symptoms that have been validated to have high specificity or sensitivity for COVID-19. It is possible, that as new variants emerge there may be changes in the patterns of symptoms that individuals display. Clinical diagnosis should therefore always be confirmed through SARS-CoV-2 laboratory testing.”

Government of Canada – COVID-19 Signs, symptoms, and severity of disease: A clinician guide

Overall, the frequency of symptoms is not well established, and symptoms may develop over time.

The incubation period for COVID-19 has been estimated to range from 2 to 14 days, with a median of 5-6 days from exposure to symptom onset. Of all individuals who develop symptoms, 97.5% of the symptoms occur within 11.5 days of exposure. Note that SARS-CoV-2 RNA may be detectable in the upper or lower respiratory tract for weeks after illness onset. However, detection of viral RNA does not necessarily mean that the patient can transmit the virus. The time period in which an individual with COVID-19 can transmit the virus is said to be at a maximum of 10 days after symptom onset for immunocompetent people who have COVID-19. Evidence has shown that an individual may be infectious for up to 3 days prior to any presentation of symptoms.

Table I depicts the reported frequency of symptoms. Source: Government of Canada

More frequent (>50%)Less frequent (<50%)Rare (<10%)
Fever (44-91%)Sputum production (28-33%)Confusion
Cough (57-74%)Muscle aches (11-44%)Runny nose
Shortness of breath (31-63%)Chest pain (16-36%)Fainting
Fatigue (31-70%)Diarrhea (5-24%)Skin manifestations
Loss of appetite (39-84%)Nausea/vomiting (5-19%)
Loss of smell and /or taste (54-88%)Headache (6-70%)
Dizziness (9-17%)
Sore throat (11-13%)

Among children, most symptoms resemble those of adults (i.e. fever, cough, and shortness of breath); there may be gastrointestinal symptoms (diarrhea, abdominal pain, nausea, and vomiting) and skin rashes. A very rare complication associated with COVID-19 infection has been seen in children: severe multisystem inflammatory syndrome (MIS-C) which share features of typical or atypical Kawasaki disease or toxic shock syndrome.

Government of Canada – COVID-19 Symptoms and Treatment (English & French)

Government of Canada – COVID-19 signs, symptoms and severity of disease: A clinician guide (English and French)

Canadian Pediatric Society – COVID-19 Information and Resources for Pediatricians (English and French)

World Health Organization – Coronavirus-Symptoms (English only)

Centers for Disease Control and Prevention – Symptoms of COVID-19 (English only)

European Centre for Disease Prevention and Control – Q & A on COVID-19 (English only)

Disease severity and risk factors for severe disease:

There is a range of COVID-19 disease severity, ranging from asymptomatic or mild, to moderate, severe and critical disease.

Data has consistently shown that older adults and those with some underlying medical conditions are at risk for serious illness. Co-morbidities most commonly associated with sever disease are hypertension, hyperlipidemia, diabetes, and chronic pulmonary disease.

“Patients with certain medical and/or social vulnerabilities, including people experiencing intellectual and developmental disabilities, persons who use substances regularly, people experience cognitive disabilities, mental health conditions or experiencing homelessness or are unhoused, may make it more difficult for the patient to recognize, clearly communicate, or act on symptom progression. These patients need closer attention and monitoring.” Source: Government of Canada

The most common comorbidities found in people with COVID-19 are shown in Table 2:

More frequent (>40%)Less frequent (<50%)Rare (<10%)
Hypertension (17%-82%)Chronic respiratory disease
Cancer (2%-7%)
Cardiovascular disease including heart failure (5%-55%)Chronic renal disease (11-14%)Atrial fibrillation/arrhythmia (3-6%)
Diabetes (4-40%)Obesity (22-29%)Gastrointestinal disease (5%)
Asthma (11%)Chronic liver disease (2-3%)
Neurologic diseases, including dementia and stroke (8-13%)

Government of Canada – COVID-19 signs, symptoms and severity of disease: A clinician guide (English and French)

Underlying conditions found to be associated with more severe COVID-19 are:

  • asthma (moderate to severe)
  • cancer
  • chronic kidney and end-stage disease
  • chronic lung diseases
  • cystic fibrosis
  • dementia or other neurological conditions
  • diabetes (type 1 or type 2)
  • Down syndrome
  • epilepsy
  • heart conditions
    • such as heart failure, coronary artery disease, cardiomyopathies or hypertension
  • HIV infection
  • immunocompromised state
  • interstitial lung disease
  • liver disease
  • motor neuron diseases
  • overweight and obesity*
  • pregnancy
  • pulmonary hypertension
  • sickle cell disease or thalassemia
  • smoking, current or former
  • solid organ or blood stem cell transplant
  • stroke or cerebrovascular disease
  • substance use disorders


There is emerging evidence of re-infection with SARS-CoV-2 due to multiple strains.

Government of Canada – COVID-19 signs, symptoms and severity of disease: A clinician guide (English and French)

Centers for Disease Control and Prevention – Reinfections and COVID-19


The main mode of transmission in human-to-human spread of SARS CoV-2 is via respiratory droplets. Respiratory secretion from an infected person, through sneezing or coughing, reaches the mucous membrane of a healthy person, causing the spread of the virus. However, transmission can also occur if a person touches an infected surface and then touches their eyes, mouth, or nose though contribution of surfaces or objects in COVID-19 transmission is not completely understood.

The role of asymptomatic, pre-symptomatic and pauci-symptomatic COVID-19 cases in the transmission is still under investigation. There is uncertainty regarding the period of infectiousness of a COVID-19 infected person but the evidence shows that an individual may be infectious for up to three days before presenting any symptoms. It has been reported that during the course of the infection, viral shedding may occur but the exact extent is unknown so far. The viral load remains the same for both children and adults suggesting that children can be as infectious as adults.

Government of Canada-Signs-Symptoms and Severity of Disease-A Clinical Guide (English & French)

Government of Canada – Coronavirus Disease (COVID-19)-For Health professionals-Transmission (English and French)

Centers for Disease Control and Prevention-How COVID-19 Spreads (English only)

World Health Organization – Coronavirus Disease (COVID-19) (English and French)

European Centre for Disease Prevention and Control – Q & A on COVID-19 (English only)

Laboratory diagnostics and reporting

Health Canada regulates the sale and import of commercial testing devices relating to COVID-19. The majority of submissions received are for 2 types of commercial testing devices: nucleic acid-based testing and serology-based testing. There is a list of testing devices that have been authorized to date for use related to COVID-19.

The Public Health Agency of Canada (PHAC) recommends the following:

Government of Canada – Reporting (English and French)

Government of Canada-National Polymerase Chain Reaction (PCR) Indication Guidance for COVID-19 (English and French)

Government of Canada-Authorized Medical Devices for uses related to COVID-19-Overview (English and French)

Government of Canada Testing devices for COVID-19: Overview (English and French)

National case definitions

To aid in early detection and containment and to characterize the clinical and epidemiologic features of COVID-19, the Public Health Agency of Canada established a national case definition. Surveillance case definitions are provided for standardized case classification and reporting to the Public Health Agency of Canada. They are based on the current level of epidemiological evidence, uncertainty, and public health response goals. They are subject to change as new information becomes available.

Please refer to the documents below to obtain information for persons under investigation (PUI), probable and confirmed case definitions, and exposure criteria and mechanisms for reporting.

Public Health Agency of Canada (PHAC) recommends the following:

Government of Canada – National case definition: Coronavirus (COVID-19) (English and French)

Government of Canada- National surveillance for Coronavirus disease (COVID-19) (English and French)

Government of Canada-Updated: Public health management of cases and contacts associated with COVID-19 (English and French)

For additional information:

CDC-Interim guidelines for collecting, handling, and testing clinical specimens from persons for Coronavirus Disease 2019 (COVID-19) (English only)

European Centre for Disease Prevention and Control-Case definition and European surveillance for COVID-19 (updated December 03, 2020) (English only)

Infection prevention and control

The Government of Canada published interim guidance for acute healthcare settings. The Public Health Agency of Canada (the Agency) develops infection prevention and control (IPC) guidelines to provide evidence-based recommendations to complement provincial/territorial public health efforts in monitoring, preventing, and controlling healthcare-associated infections. Please read in conjunction with relevant provincial, territorial, and local legislation, regulations, and policies.

Currently available scientific evidence and expert opinion informs guidance and is subject to change as new information on transmissibility and epidemiology becomes available.

Government of Canada – Infection prevention and control for novel coronavirus (COVID-19) interim guidance for acute healthcare settings (English & French)

Government of Canada-Coronavirus disease (COVID-19): For health professionals-Infection prevention and control (English & French)

Government of Canada-Public health management of cases and contacts associated with novel coronavirus disease 2019 (COVID-19) (English & French)

Government of Canada-Infection Prevention and Control for COVID-19-Interim Guidance for Outpatient and ambulatory care settings (English & French)

Government of Canada-Infection prevention & control for COVID-19: Interim guidance for long-term care homes (English & French)

For more information outside of Canada

World Health Organization – Coronavirus disease (COVID-19) Technical Guidance on Infection Prevention and Control (English only)

CDC – Interim infection prevention and control recommendations for Healthcare Personnel during the Coronavirus disease 2019 (COVID-19) Pandemic (English)

CDC – Interim Infection Prevention and Control Recommendations to Prevent SARS-CoV-2 Spread in Nursing Homes

European Centre for Disease Prevention and Control – Infection Prevention and Control and Preparedness for COVID-19 in Healthcare Settings (English only)

European Centre for Disease Prevention and Control-Contact Tracing-Public health management of persons, including health care workers, having had contact with COVID-19 cases in the European Union (English only)

Government of Canada-Infection prevention and control for COVID-19: Interim guidance for acute healthcare settings (English and French)


Canada approved the first COVID-19 vaccine on December 09, 2020 for the prevention of the disease. So far, there are four vaccines authorized for the use in Canada. This include both Viral vector-based vaccines and mRNA vaccines.

Government of Canada – COVID-19 for Healthcare Professionals – Vaccines

Government of Canada – approved COVID-19 vaccine

On November 19, 2021, Health Canada approved Pfizer BioNTech COVID-19 vaccine for children ages 5-11.

Canadian Pediatric Society – COVID-19 vaccine for children 5-11 years of age

Canada’s response and risks to Canadians

PHAC activated the Health Portfolio Operations Centre to support effective coordination of federal, provincial, and territorial preparedness and response to the emergence of COVID-19. PHAC has also published the F/P/T public health response plan for biological events, which you can reference for more information.

Government of Canada – Coronavirus Disease (COVID-19): Canada’s Response  (English & French)

Government of Canada – 2019 Novel Coronavirus: Prevention and Risks (English & French)

The government of Canada issued Reducing COVID-19 risk in community settings: A tool for operators

Travel Advisory for Canadians

The Public Health Agency of Canada (PHAC) updates Travel Advisories due to COVID-19, outlining the potential dangers to Canadian travellers and the Canadian public Travel Health Notice level 3. PHAC is recommending that Canadians should avoid all non-essential travel outside of Canada. Any person experiencing COVID-19 symptoms should seek advice from the local public health authority in their province or territory

Government of Canada – Coronavirus Disease (COVID-19): Travel advice (English & French)


Presently, “there are no drugs or vaccines authorized for COVID-19 treatment. However, Health Canada is closely monitoring all potential drugs and vaccines in the development phase in Canada and abroad by working with companies, academic research centres, and investigators to expedite the development and availability to Canadians”. According to Health Canada, in the case of hospitalized COVID-19 patients who require supplemental oxygen or mechanical ventilation, clinicians should strongly consider Intravenous Dexamethasone 6mg for 10 days (or until discharge if earlier) or equivalent glucocorticoid dose. Note: This guidance is not meant to replace clinical judgment or specialist consultation.

Government of Canada – Coronavirus disease (COVID-19) – For Health Professionals-Treatment (English & French)