Illustration of a potential vaccine against the new coronavirus SARS-CoV-2, the cause of the respiratory disease Covid-19. Nanoparticles (yellow) are covered with spike (S) proteins (blue) derived from the coronavirus. When the nanoparticles are injected into the body the proteins elicit a response from the immune system. SARS-CoV-2 emerged in Wuhan, China, in December 2019. The virus causes a mild respiratory illness that can develop into pneumonia and be fatal in some cases. The coronaviruses take their name from their crown (corona) of surface spike proteins, which are used to attach and penetrate their host cells.