SARS-CoV-2

Severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) is a strain of coronavirus that causes COVID-19, the respiratory illness responsible for the COVID-19 pandemic. The virus previously had the provisional name 2019 novel coronavirus (2019-nCoV), and has also been called human coronavirus 2019 (HCoV-19 or hCoV-19). First identified in the city of Wuhan, Hubei, China, the World Health Organization designated the outbreak a public health emergency of international concern from January 30, 2020, to May 5, 2023. SARS‐CoV‐2 is a positive-sense single-stranded RNA virus that is contagious in humans. SARS‐CoV‐2 is a virus of the species severe acute respiratory syndrome–related coronavirus (SARSr-CoV), related to the SARS-CoV-1 virus that caused the 2002–2004 SARS outbreak. Despite its close relation to SARS-CoV-1, its closest known relatives, with which it forms a sister group, are the derived SARS viruses BANAL-52 and RaTG13. Available evidence indicates that it is most likely of zoonotic origin and has close genetic similarity to bat coronaviruses, suggesting it emerged from a bat-borne virus. Research is ongoing as to whether SARS‐CoV‐2 came directly from bats or indirectly through any intermediate hosts. The virus shows little genetic diversity, indicating that the spillover event introducing SARS‐CoV‐2 to humans is likely to have occurred in late 2019. Epidemiological studies estimate that in the period between December 2019 and September 2020 each infection resulted in an average of 2.4–3.4 new infections when no members of the community were immune and no preventive measures were taken. However, some subsequent variants have become more infectious. The virus is airborne and primarily spreads between people through close contact and via aerosols and respiratory droplets that are exhaled when talking, breathing, or otherwise exhaling, as well as those produced from coughs and sneezes. It enters human cells by binding to angiotensin-converting enzyme 2 (ACE2), a membrane protein that regulates the renin–angiotensin system.