Covid-19 coronavirus vaccine. Conceptual illustration of coronavirus particles (spheres) in a petri dish (not to scale) being marked by antigens in the form of a potential vaccine, allowing them to be destroyed. 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 (previously 2019-CoV) emerged in Wuhan, China, in December 2019 and has been declared a worldwide pandemic with many thousands of deaths. The virus causes a mild respiratory illness (Covid-19) that can develop into pneumonia and be fatal in some cases. Vaccines are examples of antigens in an immunogenic form. They prime the immune system to recognise the invading pathogen, with antibodies binding to specific antigens, for instance viral proteins, marking them for destruction by phagocyte immune cells. Research is ongoing into a vaccine for the SARS-CoV-2 coronavirus, but it is not expected to be available before 2021.