|Antibodies responding to coronavirus particle. Illustration of antibodies (Y-shaped) responding to a coronavirus infection. Different strains of coronavirus are responsible for diseases such as the common cold, gastroenteritis and SARS (severe acute respiratory syndrome). The new coronavirus SARS-CoV-2 emerged in Wuhan, China, in December 2019. The virus causes a mild respiratory illness (Covid-19) that can develop into pneumonia and be fatal in some cases. As of March 2020, the virus has spread to many countries worldwide and has been declared a pandemic. Hundreds of thousands have been infected with tens of thousands of deaths. The coronaviruses take their name from their crown (corona) of surface proteins, which are used to attach and penetrate their host cells. Once inside the cells, the particles use the cells' machinery to make more copies of the virus. Antibodies bind to specific antigens, for instance viral proteins, marking them for destruction by phagocyte immune cells.