Illustration of a coronavirus particle (blue) being blocked from infecting a human cell (brown) by spheres of antibodies. Antibodies (y-shaped) are a component of the body's immune system. They recognise and bind to specific antigens, for instance viral proteins. The new coronavirus SARS-CoV-2 (previously 2019-CoV) emerged in Wuhan, China, in December 2019. The virus causes the disease Covid-19, a respiratory illness that can lead to pneumonia and can be fatal in some cases.