Quarantine

==History==

===Ancient===
An early mention of isolation occurs in the [[Biblical]] [[book of Leviticus]], written in the 7th century BC or perhaps earlier, which describes the procedure for separating out people infected with the skin disease [[Tzaraath]]. The medical nature of this isolation is, however, disputed. As traditional exegesis (dated 700 CE) sees it as a punishment for trespassing one of several negative commandment, most notably [[Lashon hara|Evil Speech]].<ref>Leviticus Rabbah 17 3</ref> A more recent hypothesis postulates that the infected are required to isolate themselves in order to prevent spread of disease{{Citation needed|date=March 2021}} (although the Bible does not imply contagiousness of ''Tzaraath''):

{{blockquote|Anyone with such a defiling disease must wear torn clothes, let their hair be unkempt, cover the lower part of their face and cry out, "Unclean! Unclean!" As long as they have the disease they remain unclean. They must live alone; they must live outside the camp.<ref>{{Bibleverse|Leviticus|13:45–46|NIV}}</ref>{{Primary source inline|date=March 2020}}<ref>[https://www.sparknotes.com/lit/oldtestament/section5/page/3/ Bible: The Old Testament – Leviticus, Numbers & Deuteronomy] ''www.sparknotes.com'', ''...the Israelites' punishment for certain infractions is to isolate or expel the offending individual from the camp... ...Since uncleanness bars a person from approaching the sacred religious items, physical impurity places one farthest from the center of Israel...'' accessed 14 March 2020</ref>}}

Moses ordered that dwellings from which infected Jews had gone should be inspected before being occupied again, and that people recovering from contagious disease were not to be allowed to go abroad until examined.{{citation needed|date=March 2023}}<ref>{{Cite web |title=Leviticus 13:1-40 - NIV - The ... |url=https://www.christianity.com/bible/niv/leviticus/13-1-40 |access-date=2023-10-17 |website=www.christianity.com |language=en}}</ref>

===Medieval Islamic world===
A [[hadith]] attributed to the Islamic prophet Muhammad advised individuals present in a region with a plague outbreak to remain in place, and advised healthy individuals to avoid traveling there.<ref>{{cite web|author=Souleymane Bachir Diagne|title=Lessons from the Hadith of the Plague|url=https://news.columbia.edu/news/islam-lessons-hadith-plague|work=[[Columbia University]] News|date=23 April 2020|department=In Brief}}</ref> The Persian Muslim polymath [[Avicenna]] argued for controlling “the spread of diseases" in his medical encyclopedia The Canon [Al-Qanun] of Medicine, published in 1025. He also recommended quarantine for patients with infectious diseases, especially [[tuberculosis]].<ref>{{cite book|author=Roy J. Shephard|title=An Illustrated History of Health and Fitness, from Pre-History to our Post-Modern World|page=279|publisher=[[Springer Publishing|Springer]]}}</ref><ref>{{Cite web|title=Ibn Sina – Ancient Hero of Modern Pandemics| date=31 May 2022| url=https://blog.frontiersin.org/2022/05/31/ibn-sina-ancient-hero-of-modern-pandemics/}}</ref><ref>{{Cite web|url=https://www.aljazeera.com/opinions/2020/6/15/what-can-avicenna-teach-us-in-time-of-coronavirus|title=What can Avicenna teach us in time of Coronavirus?|first=Hamid|last=Dabashi|website=www.aljazeera.com}}</ref>

Since the sixteenth century, the Ottoman empire has isolated travellers coming from epidemic areas during the Bubonic plague. A quarantine involved isolating healthy travellers for a period of time so that it could be ascertained if they were sick or not.<ref>{{Cite web|url=https://muslimheritage.com/plague-and-contagion/|title=Plague and Contagion|date=24 August 2020}}</ref>

The mandatory quarantine of special groups of patients, including those with leprosy, started early in Islamic history.<ref>{{cite journal|author=Arthur Saniotis|title=Islamic Medicine and Evolutionary Medicine: A Comparative Analysis|quote="Islamic medicine heralded a disciplinary model which included quarantine, hospitals and systematic clinical training."|volume=44|issue=1|journal=Journal of the Islamic Medical Association of North America|year=2012|pages=44–1–8780|doi=10.5915/44-1-8780|pmid=23864992|pmc=3708639}}</ref> In the early 8th century the sixth [[Umayyad]] [[caliph]] [[Al-Walid I]] [[Leprosarium|segregated lepers]] from the general population, with some later sources crediting the caliph with opening a [[bimaristan|hospital]]. The separation of lepers from the general population was also practiced in the Moroccan city of Fez, where lepers were relocated to a cave system outside of the city. Dedicated leprosariums were built in the time of the Ottoman sultan [[Murad II]] in the 15th century, with some of the facilities operating for centuries.<ref>{{Cite book|last1=Dunlop|first1=D.M.|last2=Colin|first2=G.S.|last3=Şehsuvaroǧlu|first3=Bedi N.|chapter=Bīmāristān|editor-first=P.|editor-last=Bearman|editor-first2=Th.|editor-last2=Bianquis|editor-first3=C.E.|editor-last3=Bosworth|editor-first4=E.|editor-last4=van Donzel|editor-first5=W.P.|editor-last5=Heinrichs|title=Encyclopaedia of Islam, Second Edition|doi= 10.1163/1573-3912_islam_COM_0123|date=24 April 2012}}</ref>

===Medieval Europe===
The word "quarantine" originates from ''quarantena'', the Venetian language form, meaning "forty days".<ref name="origin"/><ref name="Mayer"/> This is due to the 40-day isolation of ships and people practised as a measure of disease prevention related to the [[Plague (disease)|plague]].<ref name="origin"/> Between 1348 and 1359, the [[Black Death]] wiped out an estimated 30% of Europe's population, and a significant percentage of Asia's population.<ref name="origin"/> Such a disaster led governments to establish measures of [[containment]] to handle recurrent epidemics.<ref name="origin"/> A document from 1377 states that before entering the city-state of [[Republic of Ragusa|Ragusa]] in [[Dalmatia]] (modern [[Dubrovnik]] in Croatia), newcomers had to spend 30 days (a ''trentine'') in a restricted place (originally nearby islands) waiting to see whether the symptoms of Black Death would develop.<ref name="origin">{{cite journal |author= Sehdev, Paul S. |year= 2002 |title= The Origin of Quarantine |journal= Clinical Infectious Diseases |volume= 35 |issue= 9 |pages= 1071–1072 |doi= 10.1086/344062 |pmid= 12398064|doi-access= free }}</ref> In 1448 the [[Venetian Senate]] prolonged the waiting period to 40 days, thus giving birth to the term "quarantine".<ref name="JSM17">The Journal of Sociologic Medicine – Volume 17</ref> The forty-day quarantine proved to be an effective formula for handling outbreaks of the plague. Dubrovnik was the first city in Europe to set up quarantine sites such as the [[Lazzarettos of Dubrovnik]] where arriving ship personnel were held for up to 40 days.<ref>{{cite web |agency=Associated Press |title=Croatia's Dubrovnik, Home to Ancient Quarantine Facilities |url=https://www.nytimes.com/aponline/2020/03/24/world/europe/ap-eu-virus-outbreak-first-quarantine.html |website=The New York Times |access-date=1 April 2020 |date=24 March 2020}}</ref> According to current estimates, the bubonic plague had a 37-day period from infection to death; therefore, the European quarantines would have been highly successful in determining the health of crews from potential trading and supply ships.<ref>Susan Scott and Christopher Duncan, ''Biology of Plagues: Evidence from Historical Populations,'' Cambridge, United Kingdom: Cambridge University Press, 2001</ref>

Other diseases lent themselves to the practice of quarantine before and after the devastation of the plague. Those affected by [[leprosy]] were historically isolated long-term from society, and attempts were made to check the spread of [[syphilis]] in northern Europe after 1492, the advent of [[yellow fever]] in Spain at the beginning of the 19th century, and the arrival of Asiatic [[cholera]] in 1831.{{citation needed|date=March 2023}}

[[Republic of Venice|Venice]] took the lead in measures to check the spread of plague, having appointed three guardians of public health in the first years of the Black Death (1348).<ref>{{cite journal|doi=10.21061/vtuhr.v2i0.16|title=A Brief History of Quarantine|year=2013|last1=Drews|first1=Kelly|journal=The Virginia Tech Undergraduate Historical Review|volume=2|doi-access=free|hdl=10919/90277|hdl-access=free}}</ref> The next record of preventive measures comes from [[Reggio Emilia|Reggio]]/[[Modena]] in 1374. Venice founded the first [[lazaret]] (on a small island adjoining the city) in 1403. In 1467 [[Genoa]] followed the example of Venice, and in 1476 the old leper hospital of [[Marseille]] was converted into a plague hospital. The great lazaret of Marseille, perhaps the most complete of its kind, was founded in 1526 on the island of [[Frioul archipelago|Pomègues]]. The practise at all the Mediterranean lazarets did not differ from the English procedure in the Levantine and North African trade. On the arrival of cholera in 1831 some new lazarets were set up at western ports; notably, a very extensive establishment near [[Bordeaux]]. Afterwards, they were used for other purposes.{{citation needed|date=March 2023}}

===Modern history===
[[File:Quarantine guardship Rhin 1830.jpg|thumb|right|The quarantine ship ''Rhin'', at large in [[Sheerness]]. Source: [[National Maritime Museum|National Maritime Museum of Greenwich, London]]]]
Epidemics of yellow fever ravaged urban communities in North America throughout the late-eighteenth and early-nineteenth centuries, the best-known examples being the [[1793 Philadelphia yellow fever epidemic]]<ref>{{cite book |last1=Powell |first1=J. H. |title=Bring Out Your Dead: The Great Plague of Yellow Fever in Philadelphia in 1793 |date=2014 |publisher=University of Pennsylvania Press |id={{Project MUSE|32597|type=book}} |isbn=978-0-8122-9117-9 }}{{pn|date=October 2023}}</ref> and outbreaks in Georgia (1856) and Florida (1888).<ref>[http://bobarnebeck.com/history.html Arnebeck, Bob. "A Short History of Yellow Fever in the US". January 30, 2008; From ''Benjamin Rush, Yellow Fever and the Birth of Modern Medicine.''] ''bobarnebeck.com'', accessed 3 February 2020</ref> Cholera and smallpox epidemics continued throughout the nineteenth century, and plague epidemics affected Honolulu<ref>[http://www.slate.com/blogs/the_vault/2014/08/15/history_of_the_cordon_sanitaire_honolulu_hawaii_bubonic_plague_in_1899.html The Disastrous Cordon Sanitaire Used on Honolulu's Chinatown in 1900] ''www.slate.com'', accessed 3 February 2020</ref> and San Francisco from 1899 until 1901.<ref>[http://www.skubik.com/thesis%20summary.pdf Mark Skubik, "Public Health Politics and the San Francisco Plague Epidemic of 1900–1904,"] Doctoral Thesis, San Jose State University, 2002 ''www.skubik.com'', accessed 5 February 2020</ref> State governments generally relied on the ''[[Cordon sanitaire (medicine)|cordon sanitaire]]'' as a geographic quarantine measure to control the movement of people into and out of affected communities. During the [[Spanish flu|1918 influenza]] pandemic, some communities instituted [[protective sequestration]] (sometimes referred to as "reverse quarantine") to keep the infected from introducing influenza into healthy populations.<ref name="scholarcommons.usf.edu">[https://scholarcommons.usf.edu/cgi/viewcontent.cgi?article=5386&context=etd Peter Oliver Okin, "The Yellow Flag of Quarantine: An Analysis of the Historical and Prospective Impacts of Socio-Legal Controls Over Contagion,"] Doctoral dissertation, University of South Florida, January 2012; p. 232, ''scholarcommons.usf.edu'', accessed 5 February 2020</ref>  Additionally, the nature of the influenza virus that caused the 1918 pandemic gave rise to a public awareness of the dichotomy between "crowd" and "home" diseases. Simply quarantining the sick in isolation was ineffective in halting the spread of the disease, and new quarantine standards that extended regulations to public spaces became increasingly more common.<ref>{{Cite journal |last=Tomes |first=Nancy |date=2010 |title="Destroyer and Teacher": Managing the Masses During the 1918–1919 Influenza Pandemic |journal=Public Health Reports |volume=125 |issue=Suppl 3 |pages=48–62 |doi=10.1177/00333549101250S308 |pmc=2862334 |pmid=20568568 }}</ref> Most Western countries implemented a range of containment strategies, including isolation, surveillance, and the closure of schools, churches, theatres, and public events.<ref>{{cite journal |last1=Martini |first1=Mariano |last2=Gazzaniga |first2=Valentina |last3=Bragazzi |first3=Nicola Luigi |last4=Barberis |first4=Ilaria |title=The Spanish Influenza Pandemic: a lesson from the history 100 years after 1918 |journal=Journal of Preventive Medicine and Hygiene |date=2 April 2019 |volume=60 |issue=1 |pages=E64–E67 |doi=10.15167/2421-4248/jpmh2019.60.1.1205 |pmid=31041413 |pmc=6477554 }}</ref>
[[File:Romania - Isolating a village whose inhabitants believe that doctors poison those suspected of cholera.jpg|thumb|upright|Isolating a village in [[Romania]] whose inhabitants believe that doctors poison those suspected of cholera (1911)]]

People were prevented from entering the [[Ashanti Empire]] at [[border checkpoints]] if they exhibited symptoms of smallpox. Those who discovered symptoms of the disease after entering Ashanti were quarantined in remote villages.<ref>{{cite journal | last=Maier| first=D. | title=Nineteenth-Century Asante Medical Practices| journal= Comparative Studies in Society and History| volume=21 | issue=1 | pages=63–81 | year=1979| jstor=178452| doi=10.1017/S0010417500012652 | pmid=11614369 | s2cid=19587869 }}</ref>  In the 1830s, both the [[Ottoman Empire]] and [[Egypt]] established new quarantine systems. In 1831, Mehmet Ali of Egypt founded the Quarantine Board in Alexandria. In 1838, the Ottoman government installed the Supreme Council of Health, including the Quarantine Administration, in Istanbul. These two institutions set up permanent quarantines throughout the eastern Mediterranean, based on the western Mediterranean quarantine model.<ref name="Hamed-Troyansky">{{Cite journal|last=Hamed-Troyansky|first=Vladimir|date=2021|title=Ottoman and Egyptian Quarantines and European Debates on Plague in the 1830s–1840s|journal=Past and Present|volume=253|pages=235–270|doi=10.1093/pastj/gtaa017}}</ref> For example, at the port of [[İzmir]], all ships and their cargo would be inspected and those suspected of carrying the plague would be towed to separate docks and their personnel housed in separate buildings for a determined period of time. In [[Thessaly]], along the Greek-Turkish border, all travellers entering and exiting the Ottoman Empire would be quarantined for 9–15 days. Upon appearance of the plague, the quarantine stations would be militarised and the [[Ottoman army]] would be involved in border control and [[disease monitoring]].<ref>{{cite book|title=Plague and Contagion in the Islamic Mediterranean|editor=Nukhet Varlik|author=Andrew Robarts|pages=236–7|publisher=Arc Humanities Press}}</ref>

====International conventions 1852–1927====
Since 1852, several conferences were held involving European powers, with a view to uniform action in keeping out infection from the East and preventing its spread within Europe. All but that of 1897 were concerned with [[cholera]]. No result came of those at Paris (1852), Constantinople (1866), Vienna (1874), and Rome (1885), but each of the subsequent ones doctrine of constructive infection of a ship as coming from a scheduled port, and an approximation to the principles advocated by the United Kingdom for many years. The principal countries which retained the old system at the time were Spain, Portugal, Turkey, Greece, and Russia (the British possessions at the time, Gibraltar, Malta, and Cyprus, being under the same influence). The aim of each international sanitary convention had been to bind the governments to a uniform minimum of preventive action, with further restrictions permissible to individual countries. The minimum specified by international conventions was very nearly the same as the British practice, which had been in turn adapted to continental opinion in the matter of the importation of rags.{{citation needed|date=March 2023}}

The Venice convention of 30 January 1892 dealt with cholera by the [[Suez Canal]] route; that of Dresden of 15 April 1893, with cholera within European countries; that of Paris of 3 April 1894, with cholera by the pilgrim traffic; and that of Venice, on 19 March 1897, was in connection with the outbreak of plague in the East, and the conference met to settle on an international basis the steps to be taken to prevent, if possible, its spread into Europe. An additional convention was signed in Paris on 3 December 1903.<ref>[http://www.fco.gov.uk/resources/en/pdf/treaties/TS1/1907/27 Text of the 1903 convention] British Foreign and Commonwealth Office, ''www.fco.gov.uk'' {{webarchive|url=https://web.archive.org/web/20120926134555/http://www.fco.gov.uk/resources/en/pdf/treaties/TS1/1907/27 |date=26 September 2012}}, accessed 5 February 2020</ref>

A multilateral international sanitary convention was concluded at Paris on 17 January 1912.<ref>Text in ''League of Nations Treaty Series'', vol. 4, pp. 282–413.</ref> This convention was most comprehensive and was designated to replace all previous conventions on that matter. It was signed by 40 countries, and consisted of 160 articles. Ratifications by 16 of the signatories were exchanged in Paris on 7 October 1920. Another multilateral convention was signed in Paris on 21 June 1926, to replace that of 1912. It was signed by 58 countries worldwide, and consisted of 172 articles.<ref>Text in ''League of Nations Treaty Series'', vol. 78, pp. 230–349.</ref>

In Latin America, a series of regional sanitary conventions were concluded. Such a convention was concluded in Rio de Janeiro on 12 June 1904. A sanitary convention between the governments of Argentina, Brazil, Paraguay, and Uruguay was concluded in Montevideo on 21 April 1914.<ref>Text in ''League of Nations Treaty Series'', vol. 5, pp. 394–441.</ref> The convention covers cases of [[Asiatic cholera]], [[Third plague pandemic|oriental plague]] and [[yellow fever]]. It was ratified by the Uruguayan government on 13 October 1914, by the Paraguayan government on 27 September 1917 and by the Brazilian government on 18 January 1921.

Sanitary conventions were also concluded between European states. A Soviet-Latvian sanitary convention was signed on 24 June 1922, for which ratifications were exchanged on 18 October 1923.<ref>Text in ''League of Nations Treaty Series'', vol. 38, pp. 10–55.</ref> A bilateral sanitary convention was concluded between the governments of Latvia and Poland on 7 July 1922, for which ratifications were exchanged on 7 April 1925.<ref>Text in ''League of Nations Treaty Series'', vol. 37, pp. 318–339.</ref> Another was concluded between the governments of Germany and Poland in Dresden on 18 December 1922, and entered into effect on 15 February 1923.<ref>Text in ''League of Nations Treaty Series'', vo. 34, pp. 302–313.</ref> Another one was signed between the governments of Poland and Romania on 20 December 1922. Ratifications were exchanged on 11 July 1923.<ref>Text in ''League of Nations Treaty Series'', vol. 18, pp. 104–119.</ref> The Polish government also concluded such a convention with the Soviet government on 7 February 1923, for which ratifications were exchanged on 8 January 1924.<ref>Text in ''League of Nations Treaty Series'', vol. 49, pp. 286–314.</ref> A sanitary convention was also concluded between the governments of Poland and Czechoslovakia on 5 September 1925, for which ratifications were exchanged on 22 October 1926.<ref>Text in ''League of Nations Treaty Series'', vol. 58, pp. 144–177.</ref> A convention was signed between the governments of Germany and Latvia on 9 July 1926, for which ratifications were exchanged on 6 July 1927.<ref>Text in ''League of Nations Treaty Series'', vol. 63, pp. 322–361.</ref>

In 1897, the [[incubation period]] for this disease was determined and this was to be adopted for administrative purposes. The incubation period was comparatively short, some three or four days. After much discussion ten days was accepted by a majority. The principle of [[disease notification]] was unanimously adopted. Each government had to notify other governments of the existence of plague within their jurisdictions and state the measures of prevention being carried out to prevent its spread. The area declared infected was limited to the district or village where the disease prevailed, and no locality was deemed to be infected because of the importation into it of a few cases of plague while there has been no spread. It was decided during the prevalence of plague, every country had the right to close its land borders to traffic. At the [[Red Sea]], it was decided after discussion a healthy vessel could pass through the Suez Canal and continue its voyage in the Mediterranean during the incubation period of the disease and that vessels passing through the Canal in quarantine might, subject to the use of the electric light, coal up in quarantine at Port Said by night or by day, and that passengers might embark in quarantine at that port. Infected vessels, if these carry a doctor and a disinfecting stove, have a right to navigate the Canal in quarantine and subject only to the landing of those who have plague.{{citation needed|date=March 2021}}

In the 20th and 21st centuries, people suspected of carrying infectious diseases have been quarantined, as in the cases of [[Andrew Speaker]] (multi-drug-resistant tuberculosis, 2007) and [[Kaci Hickox]] (Ebola, 2014). During the [[1957–58 influenza pandemic]] and the [[1968 flu pandemic]], several countries implemented measures to control spread of the disease. In addition, the [[World Health Organization]] applied a global influenza surveillance network.<ref>{{cite journal |last1=Tognotti |first1=Eugenia |title=Lessons from the History of Quarantine, from Plague to Influenza A |journal=Emerging Infectious Diseases |date=February 2013|volume=19 |issue=2 |pages=254–259 |doi=10.3201/eid1902.120312 |pmid=23343512 |pmc=3559034 }}</ref>

During the [[1994 plague in India]], many people were quarantined. Vessels and aircraft carrying passengers were fumigated.<ref>[https://web.archive.org/web/20160206192456/http://www.tm.mahidol.ac.th/seameo/2006_37_4/21-3658.pdf Review: Surat Plague of 1994 Re-examined] archived from ''www.tm.mahidol.ac.th'', accessed 22 November 2020</ref><ref>[https://www.montana.edu/historybug/yersiniaessays/godshen.html The Surat Plague and its Aftermath] ''www.montana.edu'', accessed 22 November 2020</ref>

In the [[SARS epidemic]], thousands of Chinese people were quarantined and checkpoints to take temperatures were set up.<ref>Yanzong Huang, "The SARS Epidemic and its Aftermath in China: A Political Persecutive", ''Learning from SARS: Preparing for the Next Disease Outbreak: Workshop Summary'', Washington (DC): National Academies Press (US), 2004.</ref>

Moving infected patients to [[isolation ward]]s and home-based self-quarantine of people potentially exposed was the main way the [[Western African Ebola virus epidemic]] was ended in 2016; members of the 8th [[World Health Organization|WHO]] Emergency Committee criticised international travel restrictions imposed during the epidemic as ineffective due to difficulty of enforcement, and counterproductive as they slowed down aid efforts.<ref>{{cite report|url=https://www.who.int/mediacentre/news/statements/2015/ihr-ebola-8th-meeting/en/|title=Statement on the 8th meeting of the IHR Emergency Committee regarding the Ebola outbreak in West Africa|publisher=WHO|access-date=9 June 2016|date=|archive-date=22 December 2015|archive-url=https://web.archive.org/web/20151222223327/http://www.who.int/mediacentre/news/statements/2015/ihr-ebola-8th-meeting/en/|url-status=dead}}</ref>

The [[People's Republic of China]] has employed mass quarantines – firstly of the city of [[Wuhan]] and subsequently of all of the [[Hubei]] province (population 55.5 million) – in the [[Coronavirus disease 2019|coronavirus disease 2019 pandemic]]. After a few weeks, the Italian government imposed [[2020 Italy lockdowns|lockdowns]] for the entire country (more than 60 million people) in an attempt to stop the [[COVID-19 pandemic in Italy|spread of the disease there]]. [[India]] quarantined itself from the world for a period of one month.<ref>{{Cite news|url=https://timesofindia.indiatimes.com/india/india-quarantines-itself-from-world-for-a-month-to-fight-coronavirus/articleshow/74584811.cms|title=Coronavirus update: India quarantines itself from world for a month to fight coronavirus |first1=Sushmi |last1=Dey |website=The Times of India|date=12 March 2020 |language=en|access-date=13 March 2020 }}</ref><ref>{{Cite web|url=https://www.researchdecoded.com/covid-19-quarantine-punishment-india/|title=Know the legal aspects of breaking Quarantine order|last=Gyan|date=27 March 2020|website=Research Decoded|language=en-US|access-date=29 March 2020|archive-date=28 March 2020|archive-url=https://web.archive.org/web/20200328063523/https://www.researchdecoded.com/covid-19-quarantine-punishment-india/|url-status=dead}}</ref> Most governments around the world restricted or advised against all non-essential travel to and from countries and areas affected by the outbreak.<ref name="AutoDW-50">{{cite web |url=https://www.cdc.gov/coronavirus/2019-ncov/travelers/index.html |title=COVID-19 Information for Travel |date=11 February 2020 |work=U.S. [[Centers for Disease Control and Prevention]] (CDC) |access-date=25 February 2020}}</ref> By late 2020, the virus had already spread within communities in large parts of the world, with many not knowing where or how they were infected.<ref name="CDC-CD-transmission">{{cite web |title=Coronavirus Disease 2019 (COVID-19)—Transmission |url=https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/how-covid-spreads.html |website=U.S. [[Centers for Disease Control and Prevention]] (CDC) |access-date=29 March 2020 |date=17 March 2020}}</ref><!-- Add lockdown dates to this paragraph -->