Severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) is the virus that causes COVID-19, the respiratory illness responsible for the COVID-19 pandemic. Like other coronaviruses, SARS-CoV-2 has four structural proteins, known by the letters S (spike), E (envelope), M (membrane), and N (nucleocapsid); the N protein holds the RNA genome, and the S, E, and M proteins together create the viral envelope. This colourised transmission electron micrograph shows SARS-CoV-2 virus particles emerging from the surface of cells cultured in a laboratory. The crown-like spikes on the outer edge of the virus particles give coronaviruses their name, derived from Latin corona, 'crown'.Photograph credit: National Institute of Allergy and Infectious Diseases, Rocky Mountain Laboratories