Molecular model of the SARS-CoV-2 coronavirus spike (S) protein (red) with the B.1.531 and B.1.1.7 variant mutation sites highlighted. 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. The B.1.1.7 emerged in the UK, where, due to its increased transmissibility, it has become the predominant strain. 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.