A conductor checks a passenger's ticket and certificate of vaccination against the coronavirus disease (COVID-19) or a negative COVID-19 test before boarding a train at a railway station in Kyiv, Ukraine October 22, 2021. REUTERS/Valentyn Ogirenko

A conductor checks passengers' tickets and certificates of vaccination against the coronavirus disease (COVID-19) or negative COVID-19 tests before boarding a train at a railway station in Kyiv, Ukraine October 22, 2021. REUTERS/Valentyn Ogirenko

A man undergoes the coronavirus disease (COVID-19) rapid antigen test at a railway station in Kyiv, Ukraine October 22, 2021. REUTERS/Valentyn Ogirenko

People walk past a COVID-19 Mobile Testing Unit van, amidst the spread of the coronavirus disease (COVID-19), in London, Britain, October 21, 2021. REUTERS/Toby Melville

People walk past a COVID-19 Mobile Testing Unit van, amidst the spread of the coronavirus disease (COVID-19), in London, Britain, October 21, 2021. REUTERS/Toby Melville

Mexican Agriculture Minister Victor Villalobos, U.S. Agriculture Secretary Tom Vilsack and Charles Block, seed health testing coordinator at the Seed Science Center, view samples during a tour of the centre in Ames, Iowa, U.S., October 20, 2021. REUTERS/Tom Polansek

Mexican Agriculture Minister Victor Villalobos, U.S. Agriculture Secretary Tom Vilsack, Iowa State University President Wendy Wintersteen and Charles Block, seed health testing coordinator at the Seed Science Center, view samples during a tour of the centre in Ames, Iowa, U.S., October 20, 2021. REUTERS/Tom Polansek

A medical staff administers a nucleic acid test at a booth on a street in Beijing, China, as outbreaks of the coronavirus disease (COVID-19) continue, October 20, 2021. REUTERS/Thomas Peter

A medical staff administers a nucleic acid test at a booth on a street in Beijing, China, as outbreaks of the coronavirus disease (COVID-19) continue, October 20, 2021. REUTERS/Thomas Peter

A sign directs employees to return-to-work COVID-19 testing at the World Bank in Washington, U.S. October 19, 2021. REUTERS/Jonathan Ernst

A sign directs employees to return-to-work COVID-19 testing at the World Bank in Washington, U.S. October 19, 2021. REUTERS/Jonathan Ernst

A sign directs employees to return-to-work COVID-19 testing at the World Bank in Washington, U.S. October 19, 2021. REUTERS/Jonathan Ernst

A woman undergoes a free coronavirus disease (COVID-19) rapid antigen test at a testing centre in the State Department Store, GUM, in Moscow, Russia October 18, 2021. REUTERS/Maxim Shemetov

A woman undergoes a free coronavirus disease (COVID-19) rapid antigen test at a testing centre in the State Department Store, GUM, in Moscow, Russia October 18, 2021. REUTERS/Maxim Shemetov

A used coronavirus disease (COVID-19) rapid antigen test with negative result is pictured at a testing centre in the State Department Store, GUM, in Moscow, Russia October 18, 2021. REUTERS/Maxim Shemetov

A medical specialist performs a coronavirus disease (COVID-19) rapid antigen test at a testing centre in the State Department Store, GUM, in Moscow, Russia October 18, 2021. REUTERS/Maxim Shemetov

A man undergoes a free coronavirus disease (COVID-19) rapid antigen test at a testing centre in the State Department Store, GUM, in Moscow, Russia October 18, 2021. REUTERS/Maxim Shemetov

A woman undergoes a free coronavirus disease (COVID-19) rapid antigen test at a testing centre in the State Department Store, GUM, in Moscow, Russia October 18, 2021. REUTERS/Maxim Shemetov

A general view of the Immensa Health Clinic after a COVID-19 testing laboratory has been suspended over concerns that it has been incorrectly giving negative PCR test results to people, in Wolverhampton, Britain, October 15, 2021. REUTERS/Molly Darlington

A general view of a test centre at Immensa Health Clinic after a COVID-19 testing laboratory has been suspended over concerns that it has been incorrectly giving negative PCR test results to people, in Wolverhampton, Britain, October 15, 2021. REUTERS/Molly Darlington

A general view of the Immensa Health Clinic after a COVID-19 testing laboratory has been suspended over concerns that it has been incorrectly giving negative PCR test results to people, in Wolverhampton, Britain, October 15, 2021. REUTERS/Molly Darlington

A patient walks at the entrance of a coronavirus disease (COVID-19) testing centre in Les Sorinieres near Nantes as PCR and antigenic tests, necessary for unvaccinated to get a valid health pass, become charged, excluding medical prescriptions, in France, October 15, 2021. REUTERS/Stephane Mahe

A medical worker administers a nasal swab to a patient at a coronavirus disease (COVID-19) testing centre in Les Sorinieres near Nantes, as PCR and antigenic tests, necessary for unvaccinated to get a valid health pass, become charged, excluding medical prescriptions, in France, October 15, 2021. REUTERS/Stephane Mahe

A medical worker administers a nasal swab to a patient at a coronavirus disease (COVID-19) testing centre in Les Sorinieres near Nantes, as PCR and antigenic tests, necessary for unvaccinated to get a valid health pass, become charged, excluding medical prescriptions, in France, October 15, 2021. REUTERS/Stephane Mahe

A medical worker administers a nasal swab to a patient at a coronavirus disease (COVID-19) testing centre in Les Sorinieres near Nantes, as PCR and antigenic tests, necessary for unvaccinated to get a valid health pass, become charged, excluding medical prescriptions, in France, October 15, 2021. REUTERS/Stephane Mahe

A medical worker holds a test tube after administering a nasal swab to a patient at a coronavirus disease (COVID-19) testing centre in Les Sorinieres near Nantes, as PCR and antigenic tests, necessary for unvaccinated to get a valid health pass, become charged, excluding medical prescriptions, in France, October 15, 2021. REUTERS/Stephane Mahe

Soldiers don a prototype of the U.S. Army?s Integrated Visual Augmentation System (IVAS) during a Soldier Touchpoint 3 (STP 3) squad reconnaissance mission test training event at Fort Pickett, Virginia, U.S., October 21, 2020. Picture taken October 21, 2020. Courtney Bacon/U.S. Army via REUTERS

Soldiers don a prototype of the U.S. Army?s Integrated Visual Augmentation System (IVAS) and wield a Squad immersive Virtual Trainer (SiVT) during a training environment test event at its third Soldier Touchpoint (STP 3) at Fort Pickett, Virginia, U.S., October 21, 2020. Picture taken October 21, 2020. Courtney Bacon/U.S. Army via REUTERS

An employee at a cafe shows her COVID-19 "Green Pass" a day before it becomes obligatory for all workers either to show proof of vaccination, a negative test or recent recovery from infection to access their workplaces, in Rome, Italy, October 14, 2021. REUTERS/Guglielmo Mangiapane

An employee at an optician shop shows her COVID-19 "Green Pass" a day before it becomes obligatory for all workers either to show proof of vaccination, a negative test or recent recovery from infection to access their workplaces, in Rome, Italy, October 14, 2021. REUTERS/Guglielmo Mangiapane

Figure Skating - Beijing 2022 Winter Olympics Test Event - Asia Open Figure Skating - Capital Indoor Stadium, Beijing, China - October 14, 2021 A man wearing a face mask walks behind signage REUTERS/Tingshu Wang

Figure Skating - Beijing 2022 Winter Olympics Test Event - Asia Open Figure Skating - Capital Indoor Stadium, Beijing, China - October 14, 2021 Social distancing tape is seen on the ground at the check in desk for media personnel REUTERS/Tingshu Wang

Figure Skating - Beijing 2022 Winter Olympics Test Event - Asia Open Figure Skating - Capital Indoor Stadium, Beijing, China - October 14, 2021 China's Wang Yuchen and Huang Yihang during the Pairs REUTERS/Tingshu Wang

Figure Skating - Beijing 2022 Winter Olympics Test Event - Asia Open Figure Skating - Capital Indoor Stadium, Beijing, China - October 14, 2021 A staff member wearing a face mask looks on from the stands REUTERS/Tingshu Wang

Figure Skating - Beijing 2022 Winter Olympics Test Event - Asia Open Figure Skating - Capital Indoor Stadium, Beijing, China - October 14, 2021 China's Peng Cheng and Jin Yang during the Pairs REUTERS/Tingshu Wang

Figure Skating - Beijing 2022 Winter Olympics Test Event - Asia Open Figure Skating - Capital Indoor Stadium, Beijing, China - October 14, 2021 China's Peng Cheng and Jin Yang during the Pairs REUTERS/Tingshu Wang

Figure Skating - Beijing 2022 Winter Olympics Test Event - Asia Open Figure Skating - Capital Indoor Stadium, Beijing, China - October 14, 2021 China's Sui Wenjing and Han Cong during the Pairs REUTERS/Tingshu Wang

Figure Skating - Beijing 2022 Winter Olympics Test Event - Asia Open Figure Skating - Capital Indoor Stadium, Beijing, China - October 14, 2021 China's Wang Yuchen and Huang Yihang during the Pairs REUTERS/Tingshu Wang

Figure Skating - Beijing 2022 Winter Olympics Test Event - Asia Open Figure Skating - Capital Indoor Stadium, Beijing, China - October 14, 2021 China's Wang Yuchen and Huang Yihang during the Pairs REUTERS/Tingshu Wang REFILE - CORRECTING ID

Figure Skating - Beijing 2022 Winter Olympics Test Event - Asia Open Figure Skating - Capital Indoor Stadium, Beijing, China - October 14, 2021 Finland's Jenni Saarinen during the Women's Single Short Program REUTERS/Tingshu Wang

Figure Skating - Beijing 2022 Winter Olympics Test Event - Asia Open Figure Skating - Capital Indoor Stadium, Beijing, China - October 14, 2021 China's Hengxin Jin during the Women's Single Short Program REUTERS/Tingshu Wang

Figure Skating - Beijing 2022 Winter Olympics Test Event - Asia Open Figure Skating - Capital Indoor Stadium, Beijing, China - October 14, 2021 Chinese Taipei's Tzu-Han Ting during the Women's Single Short Program REUTERS/Tingshu Wang

Figure Skating - Beijing 2022 Winter Olympics Test Event - Asia Open Figure Skating - Capital Indoor Stadium, Beijing, China - October 14, 2021 Germany's Kristina Isaev during the Women's Single Short Program REUTERS/Tingshu Wang

Figure Skating - Beijing 2022 Winter Olympics Test Event - Asia Open Figure Skating - Capital Indoor Stadium, Beijing, China - October 14, 2021 Germany's Kristina Isaev during the Women's Single Short Program REUTERS/Tingshu Wang

Figure Skating - Beijing 2022 Winter Olympics Test Event - Asia Open Figure Skating - Capital Indoor Stadium, Beijing, China - October 14, 2021 Japan's Mai Mihara during the Women's Single Short Program REUTERS/Tingshu Wang

Figure Skating - Beijing 2022 Winter Olympics Test Event - Asia Open Figure Skating - Capital Indoor Stadium, Beijing, China - October 14, 2021 A photographer in a empty stand REUTERS/Tingshu Wang

Figure Skating - Beijing 2022 Winter Olympics Test Event - Asia Open Figure Skating - Capital Indoor Stadium, Beijing, China - October 14, 2021 China's Wang Shiyue and Liu Xinyu during the Ice Dance REUTERS/Tingshu Wang

Figure Skating - Beijing 2022 Winter Olympics Test Event - Asia Open Figure Skating - Capital Indoor Stadium, Beijing, China - October 14, 2021 China's Chen Hong and Sun Zhuoming during the Ice Dance REUTERS/Tingshu Wang

Figure Skating - Beijing 2022 Winter Olympics Test Event - Asia Open Figure Skating - Capital Indoor Stadium, Beijing, China - October 14, 2021 China's Wang Shiyue and Liu Xinyu during the Ice Dance REUTERS/Tingshu Wang

Figure Skating - Beijing 2022 Winter Olympics Test Event - Asia Open Figure Skating - Capital Indoor Stadium, Beijing, China - October 14, 2021 China's Chen Hong and Sun Zhuoming during the Ice Dance in front of an empty stand REUTERS/Tingshu Wang

Figure Skating - Beijing 2022 Winter Olympics Test Event - Asia Open Figure Skating - Capital Indoor Stadium, Beijing, China - October 14, 2021 China's Chen Hong and Sun Zhuoming during the Ice Dance REUTERS/Tingshu Wang

Figure Skating - Beijing 2022 Winter Olympics Test Event - Asia Open Figure Skating - Capital Indoor Stadium, Beijing, China - October 14, 2021 China's Chen Hong and Sun Zhuoming during the Ice Dance REUTERS/Tingshu Wang

A healthcare worker takes a nasal swab sample from a worker for a coronavirus disease (COVID-19) test, at Hanoi train station in Hanoi, Vietnam, October 13, 2021. REUTERS/Nguyen Thinh Tien

A healthcare worker takes a swab sample from a traveller for a coronavirus disease (COVID-19) test at the Ben Gurion International Airport in Lod, near Tel Aviv, Israel October 13, 2021. REUTERS/ Ronen Zvulun

A healthcare worker takes a swab sample from a traveller for a coronavirus disease (COVID-19) test at the Ben Gurion International Airport in Lod, near Tel Aviv, Israel October 13, 2021. REUTERS/ Ronen Zvulun

A healthcare worker pauses as she takes swab samples from travellers for coronavirus disease (COVID-19) testing at the Ben Gurion International Airport in Lod, near Tel Aviv, Israel October 13, 2021. REUTERS/ Ronen Zvulun

A man inquires about a coronavirus disease (COVID-19) test in lower Manhattan in New York City, U.S., October 12, 2021. REUTERS/Brendan McDermid

A man helps a nurse as she draws blood for a test from a patient suffering from dengue fever inside a dengue ward at Lady Reading Hospital in Peshawar, Pakistan, October 12, 2021. REUTERS/Fayaz Aziz

Speed Skating - Beijing 2022 Winter Olympics Test Event - Speed Skating China Open - National Speed Skating Oval, Beijing, China - October 8, 2021 China's Lan Tianhong and Gert Wierda of the Netherland's in action during the men's 5000m REUTERS/Tingshu Wang