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This composite infographic shows a TEM (transmission electron micrograph) of a MERS-CoV coronavirus on the left, and a model of a coronavirus spike on the right. These club-like projections emanating from the viral membrane are characteristic of coronaviruses, including COVID-19. This is a protein on the virus' surface (the "crown" that gives it the name corona), which enables it to enter cells. (KEYSTONE/SCIENCE SOURCE/JESSICA WILSON)