Illustration of the structure of the SARS-CoV-2 coronavirus particle. It is an enveloped RNA (ribonucleic acid, green) virus. Within the membrane are spike (S) proteins (red) that bind to receptors on the host cell membrane and facilitate the virus's entry into the cell. SARS-CoV-2 (previously 2019-nCoV) was first identified in Wuhan, China, in December 2019, and has been declared a pandemic. The virus causes the respiratory infection Covid-19, which can lead to fatal pneumonia.