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Illustration of the structure of the SARS-CoV-2 coronavirus particle. It is an enveloped RNA (ribonucleic acid) virus. Within the membrane are spike proteins, membrane proteins and envelope proteins. SARS-CoV-2 was first identified in Wuhan, China, in December 2019. The virus causes the respiratory infection Covid-19, which can lead to fatal pneumonia. (KEYSTONE/SCIENCE PHOTO LIBRARY/SIMONE ALEXOWSKI / SCIENCE PHOTO LIBRARY)