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Illustration of SARS-CoV-2 coronavirus particles. SARS-CoV-2 is an enveloped RNA (ribonucleic acid) virus. Within the membrane are spike proteins (centre, large dark spikes), membrane proteins and envelope proteins. SARS-CoV-2 causes the respiratory infection Covid-19, which can lead to fatal pneumonia. (KEYSTONE/SCIENCE PHOTO LIBRARY/JUAN GAERTNER/SCIENCE PHOTO LIBRARY)