WHO declared the COVID-19 outbreak, caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), a pandemic on March 11, 2020. Initially, superspreading events, a cruise ship in Japan, mass gathering of a religious group in South Korea, skiing resorts in Italy and Austria, and a popular pilgrimage city (Iran) contributed to the rapid dissemination globally. Since then, the rate of global spread has accelerated, and widespread epidemics have occurred in numerous countries.
The SARS-CoV-2 virus is genetically closely related to severe acute respiratory syndrome coronavirus (SARS-CoV), the first pandemic threat of a novel and deadly coronavirus that emerged in late 2002 and caused an outbreak of severe acute respiratory syndrome (SARS). SARS-CoV was highly lethal but faded out after intense public health mitigation measures.2 By contrast, the novel SARS-CoV-2 that emerged in December, 2019, rapidly caused a global pandemic. The SARS 2003 outbreak ceased in June, 2003, with a global total of 8098 reported cases and 774 deaths, and a case fatality rate of 9·7%, with most cases being acquired nosocomially. In comparison, the Middle East respiratory syndrome coronavirus (MERS-CoV)—another deadly coronavirus, but which is currently not presenting a pandemic threat—emerged in 2012, and has caused 2494 reported cases and 858 deaths in 27 countries and has a very high case fatality rate of 34%.3 Because MERS-CoV is widespread in dromedary camels, zoonotic cases continue to occur, unlike SARS-CoV, which emerged from wildlife and was eliminated from the intermediate host reservoir.
