Coloured 3D computed tomography (CT) scan (right posterior oblique view) of human lungs affected by Covid-19 atypical pneumonia (red and orange areas). Covid-19 is a respiratory infection that can lead to fatal pneumonia. It is caused by the coronavirus SARS-CoV-2, which emerged in Wuhan, China, in December 2019 and spread worldwide infecting millions of people and causing hundreds of thousands of deaths.