COVID-19 for health professionals: Transmission

On this page

• Modes of transmission
• Infectious period
• Incubation period
• Re-infection

Modes of transmission

Learn about the modes of transmission of COVID-19.

Infectious period

The time period in which an individual with COVID-19 is infectious remains uncertain. A person may be infectious for up to 3 days before showing symptoms (pre-symptomatic infectiousness).

Viral RNA levels appear to be highest just before or soon after symptom onset.

Incubation period

The incubation period ranges from 1 to 14 days. The median is 5 to 6 days between exposure and symptom onset. Most people (97.5%) develop symptoms within 11.5 days of exposure.

Re-infection

There is emerging evidence of human re-infection with SARS-CoV-2. This has been documented by individuals confirmed to have been infected by different strains of the virus. Further research is required to fully comprehend the relationship between positive antibody tests and any protection against re-infection.

Currently, we do not know:

• whether the presence of antibodies indicates immunity to re-infection, and if it does, how long that potential immunity lasts
• the potential severity of subsequent infections

Early research appears to indicate that neutralizing antibody levels can decrease following recovery from COVID-19. As serological testing for antibodies expands, the results may provide insight into re-infection and duration of immunity.

The Government of Canada launched the COVID-19 Immunity Task Force in April 2020. The task force is focused on tracking the spread of the virus in the general population and shedding light on immune responses to SARS-CoV-2 in a diversity of:

• communities
• age brackets
• populations
• occupational groups

Related links

• CIHR-PHAC-CADTH Best Brains Exchange – Transmission Routes for COVID-19: Implications for Public Health
• Biosafety advisory: SARS-CoV-2 (severe acute respiratory syndrome-related coronavirus 2)
• Evidence to support safe return to clinical practice by oral health professionals in Canada during the COVID-19 pandemic: A report prepared for the Office of the Chief Dental Officer of Canada
• Canadian Centre for Occupational Health and Safety
  • COVID-19 resources and guidance, including for federal, provincial and territorial governments
• COVID-19 disinfectants, sanitizers, cleaners and soaps
• Health Canada toolkit: COVID-19 and substance use
• Subsection 56(1) Class Exemption for Patients, Practitioners and Pharmacists Prescribing and Providing Controlled Substances in Canada during the Coronavirus Pandemic