Fig. 3.

Schematic representation of the natural history of COVID-19 from the onset to recovery or death. There are basically three stages or phases in the natural history of COVID-19, regarding disease severity. The first phase is related to the onset of the disease and is generally characterized by the development of influenza-like symptoms from mild to moderate. Some individuals recover and some progress to the second phase. In this phase, it is possible to detect pneumonia-like symptoms evidenced as lung opacities as seen in chest radiography or as glass opacities in computed tomography (CT). Depending on the severity of phase 2 patients can improve or worsen with the necessity of intubation and ventilation. These patients are typical examples of the phase 3 which is characterized by hyperinflammation and sepsis of lungs and patient often requires intensive care unit (ICU) and most of them unfortunately can not overcome the infection and eventually die.