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Coloured transmission electron micrograph (TEM) of a B.1.1.7 variant Covid-19 coronavirus particles (red, round) isolated from a patient. Covid-19 is a respiratory infection that can lead to fatal pneumonia. It first emerged in Wuhan, China, in December 2019. The B.1.1.7 variant was first identified in the UK in December 2020 and has since been found in other countries. B.1.1.7 spreads between people much more quickly than other strains, but does not appear to cause more severe disease. Spike proteins (orange) in the viral envelope allow the virus to bind to host cells and infect them. (KEYSTONE/SCIENCE PHOTO LIBRARY/National Institute of Allergy and Infectious Diseases/NATIONAL INSTITUTES OF HEALTH/SCIENCE PHOTO LIBRARY)