The time between infection with the Virus or other infectious organism (when the infectious organism enters the body) and the first onset of clinical symptoms is known as the 'incubation period.' For COVID 19, WHO estimates that this period varies between 0-14 days. The time frame may differ between individuals, for example, because of differences in the dose, or amount, of infectious material, transmitted or other factors that differ between hosts, such as their immune system status.

Development and persistence of symptoms do not necessarily correspond with the time period in which the infected person can transmit the infectious agent (the infectious period).

The figure below represents the concept of the incubation period relative to the infectious period. The exact relationship between the incubation period and infectious period for COVID 19 is not well understood, and only approximate and individual cases might differ.