Three stages of COVID-19 transmission

The WHO recognises three stages of COVID-19 transmission — asymptomatic, presymptomatic and symptomatic.

  1. “Symptomatic transmission refers to transmission from a person while they are experiencing symptoms. Data from published epidemiology and virologic studies provide evidence that COVID -19 is primarily transmitted from symptomatic people to others who are in close contact through respiratory droplets, by direct contact with infected persons, or by contact with contaminated objects and surfaces,” the WHO says. The incubation period of the virus ranges between 5-14 days. Presymptomatic transmission is when a person spreads the disease before symptoms appear, and eventually develops symptoms themselves.
  2. On asymptomatic transmission, the WHO says it “refers to transmission of the virus from a person, who does not develop symptoms. There are few reports of laboratory-confirmed cases who are truly asymptomatic, and to date, there has been no documented asymptomatic transmission. This does not exclude the possibility that it may occur. Asymptomatic cases have been reported as part of contact tracing efforts in some countries.”
  3. The US Centers for Disease Control and Prevention (CDC) is clear that both presymptomatic and asymptomatic transmission of the virus are possible. “The onset and duration of viral shedding and the period of infectiousness for COVID-19 are not yet known. It is possible that SARS-CoV-2 RNA may be detectable in the upper or lower respiratory tract for weeks after illness onset, similar to infections with MERS-CoV and SARS-CoV. However, detection of viral RNA does not necessarily mean that infectious virus is present. There are reports of asymptomatic infections (detection of virus with no development of symptoms) and pre-symptomatic infections (detection of virus prior to development of symptoms) with SARS-CoV-2, but their role in transmission is not yet known. Based on existing literature, the incubation period (the time from exposure to development of symptoms) of SARS-CoV-2 and other coronaviruses (eg MERS-CoV, SARS-CoV) ranges from 2-14 days,” the CDC says.

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