COVID-19 (coronavirus disease): For health professionals
On this page
- Key information
- Transmission
- Clinical manifestations
- Diagnosis
- Treatment
- Prevention and control
- Surveillance
- Guidance resources
Key information
COVID-19 is a respiratory illness caused by the SARS-CoV-2 virus that continues to circulate globally. In Canada, COVID-19 activity can occur year-round with periodic increases. The timing and intensity of these increases can vary across regions and there remains uncertainty about the virus’s seasonal patterns. In recent years, updated COVID-19 vaccines have been made available annually in advance of the fall/winter respiratory virus season.
Getting vaccinated against COVID-19 can help reduce the risk of severe illness, including hospitalization and death, as well as post-COVID-19 condition.
Who is most at risk
Certain people are at increased risk of exposure to COVID-19 or severe disease from COVID-19, including:
- all adults 65 years of age or older
- residents of long-term care homes or other congregate living setting
- individuals who are immunocompromised due to:
- an underlying medical condition, such as cancer or HIV
- taking medications that reduce their immune response, such as chemotherapy or corticosteroids
- receipt of a solid organ or blood stem cell transplant
- individuals living with underlying medical conditions, including:
- asthma (moderate to severe)
- dementia
- diabetes (type 1 and type 2)
- heart disease
- high blood pressure
- kidney disease
- liver disease
- lung disease
- stroke
- mental health disorders
- obesity (body mass index of 40 or greater)
- Down syndrome
- individuals who are pregnant
- individuals from First Nations, Inuit and Métis communities
- healthcare workers and other care providers in facilities and community settings
- members of racialized and other equity-denied communities
Learn more:
- COVID-19: Canadian respiratory virus surveillance report
- COVID-19 variants: National Wastewater Monitoring of Pathogens
Transmission
COVID-19 is primarily spread when a person who is infected releases infectious respiratory particles of various sizes into the air. It can also be spread through contact with contaminated surfaces and objects.
The infectious period can be variable for COVID-19. It is generally considered to start about 2 days before symptom onset and can last up to 10 days following symptom onset. Sometimes, this period is longer, particularly for people who experience severe disease or who are immunocompromised. People are most infectious in the few days before or after symptom onset. Infectiousness then gradually decreases.
Clinical manifestations
The incubation period of SARS-CoV-2 has an average duration of about 2 to 4 days. COVID-19 can present with a range of clinical manifestations, which range from asymptomatic to mild or severe disease, and vary by factors such as age and vaccination status.
Common symptoms include:
- runny nose
- new or worsening cough
- sore throat
- sneezing
- headache
Other symptoms may include:
- joint and muscle pain
- chills
- fever
- dizziness
- gastrointestinal symptoms (for instance, nausea, diarrhea, abdominal pain)
- hoarse voice
- new loss of or altered sense of smell
- shortness of breath or difficulty breathing
Patients with mild disease should be informed to seek medical attention should they experience any of the following:
- trouble breathing or severe shortness of breath
- persistent pressure or pain in the chest
- new onset of confusion or altered level of consciousness
- inability to wake up or stay awake
- pale, gray, or blue-coloured skin, lips, or nail beds
Complications
Complications of COVID-19 can include:
- severe illness requiring hospitalization
- death
Multisystem inflammatory syndrome is a rare complication that has been documented among children (MIS-C) and adults (MIS-A). It can occur 2 to 6 weeks after COVID-19 infection. The syndrome is characterized by hyperinflammation and multi-organ involvement.
Some people may experience post COVID-19 condition, which is when long-term symptoms persist after recovering from the initial infection. Detailed information on post COVID-19 condition (also known as long COVID) is available.
Post COVID-19 condition (long COVID): For health professionals
Re-infection
An individual who has been previously infected or vaccinated can become re-infected because their immune response wanes over time and the virus continues to evolve. Keeping up to date with COVID-19 vaccination helps to protect from re-infection.
Diagnosis
In most outpatient settings, the diagnosis is clinical, and specific laboratory testing is not done. Some people may self-test (for example through antigen tests) for a diagnosis. Often a person admitted to hospital is tested with a nasopharyngeal swab for COVID-19.
Learn more:
- National case definition: Coronavirus disease (COVID-19)
- Biosafety advisory: SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2)
- Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2): Infectious substances pathogen safety data sheet
Treatment
COVID-19 treatments can broadly be classified into drugs that inhibit the multiplication of the virus and drugs that alleviate the symptoms of COVID-19.
Several COVID-19 treatments have been authorized by Health Canada and are available in all provinces and territories:
Learn more:
Prevention and control
Vaccination
COVID-19 vaccination helps reduce the risk of severe disease, including hospitalization and death.
The National Advisory Committee on Immunization (NACI) strongly recommends the COVID-19 vaccine for those at increased risk of severe disease due to COVID-19. All other individuals 6 months of age and over may receive the COVID-19 vaccine.
Health care providers are encouraged to discuss the benefits and possible side effects of the COVID-19 vaccine with patients, as well as the risks of not being vaccinated.
Learn more:
- Approved COVID-19 vaccines
- COVID-19: NACI statements and publications
- COVID-19 vaccines: Canadian Immunization Guide
- COVID-19 vaccines: Planning guidance for immunization clinics
- Archived: Canada’s COVID-19 Immunization Plan: Saving Lives and Livelihoods
- Anaphylaxis and COVID-19: Summary information for health care professionals
- Archived: COVID-19 immunization: Federal, provincial and territorial statement of common principles
- Reporting ocular adverse events following COVID‐19 vaccination: Communiqué to healthcare professionals (May 30, 2022)
Personal protective measures
Health care providers can encourage patients to use personal protective measures alongside vaccination to reduce the risk of getting or spreading COVID-19 and other respiratory infectious diseases. Personal protective measures include:
- staying home when sick or infected
- wearing a well-fitting respirator or mask when appropriate
- improving indoor ventilation when possible
- cleaning hands regularly
- covering coughs and sneezes with a tissue or their elbow
- cleaning and disinfecting high-touch surfaces and objects regularly
Learn more:
Surveillance
FluWatch+ surveillance
FluWatch+ is Canada's national surveillance system that monitors the spread of respiratory viruses, such as:
- COVID-19
- seasonal flu (influenza)
- respiratory syncytial virus (RSV)
- other respiratory viruses
The FluWatch+ surveillance system has an interactive dashboard. This technical dashboard provides a weekly overview of key trends on the activity of respiratory viruses.
Learn more:
- National surveillance for COVID-19
- Respiratory virus monitoring in Canada
- National case definition: Coronavirus disease (COVID-19)
International surveillance
The World Health Organization (WHO) has current international respiratory activity data.
Guidance resources
We have developed infection prevention and control guidance and strategies to prevent or limit COVID-19 transmission in healthcare settings.
All healthcare settings
Acute care
Indigenous health care
Long-term care
- COVID-19: Guidance on pets and long-term care homes
- Interim guidance: Infection prevention and control for COVID-19 for long-term care homes
- Using ventilation and filtration to reduce aerosol transmission of COVID-19 in long-term care homes
- Updated guidance for infection prevention and control in healthcare settings when COVID-19 is suspected or confirmed (April 2024)