COVID-19

== Cause ==
COVID‑19 is caused by infection with a [[Strain (biology)#Microbiology and virology|strain]] of [[coronavirus]] known as "severe acute respiratory syndrome coronavirus 2" ([[SARS-CoV-2]]).<ref>{{#invoke:cite journal ||vauthors=Hu B, Guo H, Zhou P, Shi ZL |date=March 2021 |title=Characteristics of SARS-CoV-2 and COVID-19 |journal=Nature Reviews. Microbiology |volume=19 |issue=3 |pages=141–154 |doi=10.1038/s41579-020-00459-7 |pmc=7537588 |pmid=33024307}}</ref>

=== Transmission ===
{{Main|Transmission of COVID-19}}
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[[File:Https-doi.org-10.1073-pnas.2009637117-F4.large.jpg|thumb|[[Transmission (medicine)|Transmission]] of COVID‑19]]
{{Excerpt|Transmission of COVID-19|paragraphs=1-4|hat=no}}

=== Virology ===
{{Main|SARS-CoV-2}}[[File:Coronavirus virion structure.svg|thumb|Illustration of [[SARSr-CoV]] [[Virus|virion]]]]

Severe acute respiratory syndrome coronavirus{{spaces}}2 (SARS-CoV-2) is a [[novel virus|novel]] severe acute respiratory syndrome coronavirus. It was first isolated from three people with pneumonia connected to the [[Disease cluster|cluster]] of acute respiratory illness cases in Wuhan.<ref name="ECDC risk assessment">{{#invoke:Cite web||url=https://www.ecdc.europa.eu/sites/default/files/documents/SARS-CoV-2-risk-assessment-14-feb-2020.pdf |title=Outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2): increased transmission beyond China – fourth update |publisher=European Centre for Disease Prevention and Control |date=14 February 2020 |access-date=8 March 2020}}</ref> All structural features of the novel SARS-CoV-2 virus particle occur in related [[coronavirus]]es in nature,<ref name="NM-20200317" /> particularly in ''[[Rhinolophus sinicus]]'' aka Chinese horseshoe bats.<ref name="zhou20">{{#invoke:cite journal ||doi=10.1038/s41586-020-2012-7|title=A pneumonia outbreak associated with a new coronavirus of probable bat origin |year=2020 |last1=Zhou |first1=Peng |last2=Yang |first2=Xing-Lou |last3=Wang |first3=Xian-Guang |last4=Hu |first4=Ben |last5=Zhang |first5=Lei |last6=Zhang |first6=Wei |last7=Si |first7=Hao-Rui |last8=Zhu |first8=Yan |last9=Li |first9=Bei |last10=Huang |first10=Chao-Lin |last11=Chen |first11=Hui-Dong |last12=Chen |first12=Jing |last13=Luo |first13=Yun |last14=Guo |first14=Hua |last15=Jiang |first15=Ren-Di |last16=Liu |first16=Mei-Qin |last17=Chen |first17=Ying |last18=Shen |first18=Xu-Rui |last19=Wang |first19=Xi |last20=Zheng |first20=Xiao-Shuang |last21=Zhao |first21=Kai |last22=Chen |first22=Quan-Jiao |last23=Deng |first23=Fei |last24=Liu |first24=Lin-Lin |last25=Yan |first25=Bing |last26=Zhan |first26=Fa-Xian |last27=Wang |first27=Yan-Yi |last28=Xiao |first28=Geng-Fu |last29=Shi |first29=Zheng-Li |journal=Nature |volume=579 |issue=7798 |pages=270–273 |pmid=32015507 |pmc=7095418 |bibcode=2020Natur.579..270Z }}</ref>

Outside the human body, the virus is destroyed by household soap which bursts its [[Viral envelope|protective bubble]].<ref name="NatGeoSoap">{{#invoke:Cite web||url=https://www.nationalgeographic.com/science/2020/03/why-soap-preferable-bleach-fight-against-coronavirus/ |vauthors=Gibbens S |title=Why soap is preferable to bleach in the fight against coronavirus |date=18 March 2020 |website=[[National Geographic]] |url-status=live |archive-url=https://web.archive.org/web/20200402001042/https://www.nationalgeographic.com/science/2020/03/why-soap-preferable-bleach-fight-against-coronavirus/ |archive-date=2 April 2020 |access-date=2 April 2020}}</ref> Hospital disinfectants, alcohols, heat, [[povidone-iodine]], and [[Ultraviolet|ultraviolet-C]] (UV-C) irradiation are also effective disinfection methods for surfaces.<ref>{{#invoke:cite journal ||last1=Viana Martins |first1=C. P. |last2=Xavier |first2=C. S. F. |last3=Cobrado |first3=L. |date=2022 |title=Disinfection methods against SARS-CoV-2: a systematic review |url= |journal=The Journal of Hospital Infection |volume=119 |pages=84–117 |doi=10.1016/j.jhin.2021.07.014 |issn=1532-2939 |pmc=8522489 |pmid=34673114}}</ref>

SARS-CoV-2 is closely related to the original [[SARS-CoV]].<ref name="Zhu24Jan2020">{{#invoke:cite journal ||vauthors=Zhu N, Zhang D, Wang W, Li X, Yang B, Song J, Zhao X, Huang B, Shi W, Lu R, Niu P, Zhan F, Ma X, Wang D, Xu W, Wu G, Gao GF, Tan W |title=A Novel Coronavirus from Patients with Pneumonia in China, 2019 |journal=The New England Journal of Medicine |volume=382 |issue=8 |pages=727–733 |date=February 2020 |pmid=31978945 |pmc=7092803 |doi=10.1056/NEJMoa2001017}}</ref> It is thought to have an animal ([[Zoonosis|zoonotic]]) origin. Genetic analysis has revealed that the coronavirus genetically clusters with the genus ''[[Betacoronavirus]]'', in subgenus [[Severe acute respiratory syndrome–related coronavirus|''Sarbecovirus'']] (lineage B) together with two bat-derived strains. It is 96% identical at the whole [[genome]] level to other bat coronavirus samples (BatCov [[RaTG13]]).<ref name="WHOReport24Feb2020">{{#invoke:cite report ||url=https://www.who.int/docs/default-source/coronaviruse/who-china-joint-mission-on-covid-19-final-report.pdf |title=Report of the WHO-China Joint Mission on Coronavirus Disease 2019 (COVID-19) |date=February 2020 |publisher=[[World Health Organization]] (WHO) |access-date=21 March 2020 |archive-url=https://web.archive.org/web/20200229221222/https://www.who.int/docs/default-source/coronaviruse/who-china-joint-mission-on-covid-19-final-report.pdf |archive-date=29 February 2020 |url-status=live}}</ref><ref>{{#invoke:Cite web|| title=Report of the WHO-China Joint Mission on Coronavirus Disease 2019 (COVID-19) | publisher=[[World Health Organization]] (WHO) | url=https://www.who.int/publications/i/item/report-of-the-who-china-joint-mission-on-coronavirus-disease-2019-(covid-19) | access-date=25 January 2022}}</ref><ref name="RathoreSingh">{{#invoke:cite journal || vauthors = Rathore JS, Ghosh C | title = Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), a newly emerged pathogen: an overview | journal = Pathogens and Disease | volume = 78 | issue = 6 | date = August 2020 | pmid = 32840560 | pmc = 7499575 | doi = 10.1093/femspd/ftaa042 | oclc = 823140442 | doi-access = free | title-link = doi }}</ref> The structural proteins of SARS-CoV-2 include [[coronavirus membrane protein|membrane glycoprotein]] (M), [[coronavirus envelope protein|envelope protein]] (E), [[coronavirus nucleocapsid protein|nucleocapsid protein]] (N), and the [[coronavirus spike protein|spike protein]] (S). The M protein of SARS-CoV-2 is about 98% similar to the M protein of bat SARS-CoV, maintains around 98% homology with pangolin SARS-CoV, and has 90% homology with the M protein of SARS-CoV; whereas, the similarity is only around 38% with the M protein of MERS-CoV.<ref>{{#invoke:cite journal || vauthors = Thomas S | title = The Structure of the Membrane Protein of SARS-CoV-2 Resembles the Sugar Transporter SemiSWEET | journal = Pathogens & Immunity | volume = 5 | issue = 1 | pages = 342–363 | date = October 2020 | pmid = 33154981 | pmc = 7608487 | doi = 10.20411/pai.v5i1.377 }}</ref>

=== SARS-CoV-2 variants ===
{{Main|Variants of SARS-CoV-2}}

The many thousands of SARS-CoV-2 variants are grouped into either [[clade]]s or [[Lineage (evolution)|lineages]].<ref>{{#invoke:cite journal ||vauthors = Koyama T, Platt D, Parida L |title=Variant analysis of SARS-CoV-2 genomes |journal=Bulletin of the World Health Organization |volume=98 |issue=7 |pages=495–504 |date=July 2020 |pmid=32742035 |pmc=7375210 |doi=10.2471/BLT.20.253591 |quote=We detected in total 65776 variants with 5775 distinct variants.}}</ref><ref name="Rambaut-2020"/> The WHO, in collaboration with partners, expert networks, national authorities, institutions and researchers, have established nomenclature systems for naming and tracking SARS-CoV-2 genetic lineages by [[GISAID]], [[Nextstrain]] and [[Phylogenetic Assignment of Named Global Outbreak Lineages|Pango]]. The expert group convened by the WHO recommended the labelling of variants using letters of the [[Greek alphabet]], for example, [[SARS-CoV-2 Alpha variant|Alpha]], [[SARS-CoV-2 Beta variant|Beta]], [[SARS-CoV-2 Delta variant|Delta]], and [[SARS-CoV-2 Gamma variant|Gamma]], giving the justification that they "will be easier and more practical to discussed by non-scientific audiences".<ref>{{#invoke:Cite web||date=1 July 2021|title=Tracking SARS-CoV-2 variants|url=https://www.who.int/activities/tracking-SARS-CoV-2-variants|access-date=5 July 2021|website=[[World Health Organization]]}}</ref> [[Nextstrain]] divides the variants into five clades (19A, 19B, 20A, 20B, and 20C), while [[GISAID]] divides them into seven (L, O, V, S, G, GH, and GR).<ref name="Alm2020Aug">{{#invoke:cite journal ||vauthors=Alm E, Broberg EK, Connor T, Hodcroft EB, Komissarov AB, Maurer-Stroh S, Melidou A, Neher RA, O'Toole Á, Pereyaslov D |title=Geographical and temporal distribution of SARS-CoV-2 clades in the WHO European Region, January to June 2020 |journal=Euro Surveillance |volume=25 |issue=32 |date=August 2020 |pmid=32794443 |pmc=7427299 |doi=10.2807/1560-7917.ES.2020.25.32.2001410}}</ref> The Pango tool groups variants into [[Lineage (evolution)|lineages]], with many circulating lineages being classed under the B.1 lineage.<ref name="Rambaut-2020">{{#invoke:cite journal ||vauthors=Rambaut A, Holmes EC, O'Toole Á, Hill V, McCrone JT, Ruis C, du Plessis L, Pybus OG |title=A dynamic nomenclature proposal for SARS-CoV-2 lineages to assist genomic epidemiology |journal=Nature Microbiology |volume=5 |issue=11 |pages=1403–1407 |date=November 2020 |pmid=32669681 |pmc=7610519 |doi=10.1038/s41564-020-0770-5}}</ref><ref>{{#invoke:Cite web||title=PANGO lineages|url=https://cov-lineages.org/pango_lineages.html|access-date=9 May 2021|url-status=dead |website=cov-lineages.org|archive-date=10 May 2021|archive-url=https://web.archive.org/web/20210510111318/https://cov-lineages.org/pango_lineages.html}}</ref>

Several notable variants of SARS-CoV-2 emerged throughout 2020.<ref name="Lauring Hodcroft 2021 pp. 529–531">{{#invoke:cite journal ||vauthors=Lauring AS, Hodcroft EB |title=Genetic Variants of SARS-CoV-2-What Do They Mean? |journal=JAMA |volume=325 |issue=6 |pages=529–531 |date=February 2021 |pmid=33404586 |s2cid=230783233 |doi=10.1001/jama.2020.27124 |doi-access=free |title-link=doi}}</ref><ref name="Abdool Karim de Oliveira pp. 1866–1868">{{#invoke:cite journal ||vauthors=Abdool Karim SS, de Oliveira T |title=New SARS-CoV-2 Variants – Clinical, Public Health, and Vaccine Implications |journal=The New England Journal of Medicine |volume=384 |issue=19 |pages=1866–1868 |date=May 2021 |pmid=33761203 |doi=10.1056/nejmc2100362| issn=0028-4793 |publisher=Massachusetts Medical Society |pmc=8008749}}</ref> [[Cluster 5]] emerged among [[mink]]s and mink farmers in [[Denmark]].<ref>{{#invoke:cite journal ||vauthors=Mallapaty S |title=COVID mink analysis shows mutations are not dangerous – yet |journal=Nature |volume=587 |issue=7834 |pages=340–341 |date=November 2020 |pmid=33188367 |doi=10.1038/d41586-020-03218-z |doi-access=free |s2cid=226947606 |bibcode=2020Natur.587..340M}}</ref> After strict quarantines and a mink euthanasia campaign, the cluster was assessed to no longer be circulating among humans in Denmark as of 1 February 2021.<ref>{{#invoke:cite journal ||vauthors=Larsen HD, Fonager J, Lomholt FK, Dalby T, Benedetti G, Kristensen B, Urth TR, Rasmussen M, Lassaunière R, Rasmussen TB, Strandbygaard B, Lohse L, Chaine M, Møller KL, Berthelsen AN, Nørgaard SK, Sönksen UW, Boklund AE, Hammer AS, Belsham GJ, Krause TG, Mortensen S, Bøtner A, Fomsgaard A, Mølbak K |title=Preliminary report of an outbreak of SARS-CoV-2 in mink and mink farmers associated with community spread, Denmark, June to November 2020 |journal=Euro Surveillance |volume=26 |issue=5 |pages=2100009 |date=February 2021 |pmid=33541485 |pmc=7863232 |doi=10.2807/1560-7917.ES.2021.26.5.210009 |quote=As at 1 February 2021, we assess that the cluster 5 variant is no longer circulating among humans in Denmark.}}</ref>

{{as of|2021|12}}, there are five dominant variants of SARS-CoV-2 spreading among global populations: the [[SARS-CoV-2 Alpha variant|Alpha variant]] (B.1.1.7, formerly called the UK variant), first found in London and Kent, the [[SARS-CoV-2 Beta variant|Beta variant]] (B.1.351, formerly called the South Africa variant), the [[SARS-CoV-2 Gamma variant|Gamma variant]] (P.1, formerly called the Brazil variant), the [[SARS-CoV-2 Delta variant|Delta variant]] (B.1.617.2, formerly called the India variant),<ref>{{#invoke:Cite web||title=New COVID-19 Variants|url=https://www.cdc.gov/coronavirus/2019-ncov/transmission/variant.html|access-date=15 July 2021|website=U.S. [[Centers for Disease Control and Prevention]] (CDC)|date=28 June 2021|orig-date=First published 11 February 2020}}</ref> and the [[SARS-CoV-2 Omicron variant|Omicron variant]] (B.1.1.529), which had spread to 57 countries as of 7 December.<ref>{{#invoke:Cite web||url=https://www.who.int/publications/m/item/weekly-epidemiological-update-on-covid-19---7-december-2021 |title=COVID-19 Weekly Epidemiological Update Edition 69 |website=[[World Health Organization]] (WHO) |date=7 December 2021}}</ref><ref>{{#invoke:Cite web||title=Classification of Omicron (B.1.1.529): SARS-CoV-2 Variant of Concern |url=https://www.who.int/news/item/26-11-2021-classification-of-omicron-(b.1.1.529)-sars-cov-2-variant-of-concern |access-date=9 December 2021 |website=[[World Health Organization]] (WHO)}}</ref>

On December 19, 2023, the WHO declared that another distinctive variant, JN.1, had emerged as a "variant of interest". Though the WHO expects an increase in cases globally, particularly for countries entering winter, the current overall global health risk (as of December 21, 2023) remains low.<ref>{{#invoke:Cite web ||author-link=World Health Organization |date=December 19, 2023 |title=JN.1 |url=https://www.who.int/docs/default-source/coronaviruse/18122023_jn.1_ire_clean.pdf?sfvrsn=6103754a_3 |access-date=December 21, 2023}}</ref><ref>{{#invoke:Cite web ||last=Benadjaoud |first=Youri |date=2023-12-19 |title=COVID variant JN.1 listed as 'variant of interest' by World Health Organization |url=https://abcnews.go.com/Health/covid-variant-jn1-listed-variant-interest-world-health/story?id=105782742 |access-date=2023-12-22 |website=ABC News |language=en}}</ref>