Molecular model of the SARS-CoV-2 coronavirus spike (S) protein (red) from the B.1.531 variant, showing its mutation site (yellow). S proteins are found in the viral membrane, they bind to angiotensin converting enzyme 2 receptors (ACE2, blue) on host cell membranes and facilitate the virus's entry to the cell. The B.1.531 strain of the virus emerged in South Africa. Its E484K mutation may help it evade the immune system. SARS-CoV-2 emerged in Wuhan, China, in December 2019. The virus causes the disease Covid-19, a respiratory illness that can lead to pneumonia and can be fatal in some cases.