The unprecedented outbreak of coronavirus disease 2019 (COVID-19) was declared a pandemic by the WHO, with >34 million people infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes COVID-19, and with>1 million COVID-19-related deaths worldwide 1. COVID-19 can lead to a disease spectrum ranging from mild respiratory symptoms to acute respiratory distress syndrome (ARDS) and death 2-4. SARS-CoV-2 is now the third highly pathogenic and transmissible coronavirus identified in humans. Human coronaviruses were first dis covered in the 1960s 5 , but it was not until the 21st century that coronaviruses were recognized as major threats to public health. SARS-CoV 6-9 , Middle East respiratory syndrome coronavirus (MERS-CoV) 10 and SARS-CoV-2 all cause severe respiratory tract infections and have been associated with global pandemics. SARS-CoV was first reported in China in 2003 and infected >8,000 indivi duals, causing 774 deaths worldwide 11. A decade later, MERS was first reported in Saudi Arabia and infected >2,494 individuals and caused 858 deaths, with an extremely high death rate of 34% in part owing to the lack of effective therapies 12,13. SARS-CoV, MERS-CoV and SARS-CoV-2 belong to the Betacoronavirus genus, which is one of four genera of coronavirus 14. Phylogenetic analysis revealed that SARS-CoV-2 is closely related to two bat-derived SARS-like coronaviruses, bat-SL-CoVZC45 and bat-SL-CoVZXC21 (with around 88% sequence identity), SARS-CoV (approximately 79% sequence identity) and MERS-CoV (approximately 50% sequence identity) 15. Homology modelling revealed that the receptor-binding domain structures in SARS-CoV and SARS-CoV-2 are similar, despite some amino acid variations 15. MERS-CoV infects human cells by binding to the dipeptidyl peptidase 4 receptor 16 , whereas both SARS-CoV 17 and SARS-CoV-2 (refs 18,19) use angiotensin-converting enzyme 2 (ACE2) as a receptor to infect cells. For SARS-CoV-2 infection, in addition to ACE2, one or more proteases including transmembrane protease serine 2 (TMPRSS2), basigin (also known as CD147) and potentially cathepsin B or cathepsin L are required 18,19. Acute respiratory distress syndrome (ArDs). A syndrome characterized by severe acute respiratory failure arising from inflammation and fluid build-up in the lungs.