A volunteer holds a sign to alert participants to follow COVID-19 control measures at the Tiananmen Square before the Beijing Marathon, the first in two years after being cancelled in 2020 and 2021 because of the coronavirus disease (COVID-19), in Beijing, China November 6, 2022. REUTERS/Tingshu Wang 

Volunteers form a human chain to guide participants at the entrance of the Tiananmen Square before the Beijing Marathon, the first in two years after being cancelled in 2020 and 2021 because of the coronavirus disease (COVID-19), in Beijing, China November 6, 2022. REUTERS/Tingshu Wang 

Volunteers form a human chain to guide participants at the entrance of the Tiananmen Square before the Beijing Marathon, the first in two years after being canceled in 2020 and 2021 because of the coronavirus disease (COVID-19), in Beijing, China November 6, 2022. REUTERS/Tingshu Wang 

Volunteers arrive to a primary school repurposed for virus control efforts in Futian district, following the coronavirus disease (COVID-19) outbreak in Shenzhen, Guangdong province, China August 31, 2022. REUTERS/David Kirton 

Parents and volunteers repaint school chairs in preparation for the resumption of face-to-face classes in an elementary school in Quezon City, Philippines, August 5, 2022. REUTERS/Eloisa Lopez 

Parents and volunteers repaint school chairs in preparation for the resumption of face-to-face classes in an elementary school in Quezon City, Philippines, August 5, 2022. REUTERS/Eloisa Lopez 

Parents and volunteers repaint school chairs in preparation for the resumption of face-to-face classes in an elementary school in Quezon City, Philippines, August 5, 2022. REUTERS/Eloisa Lopez 

Volunteers clean up by the Pyramid stage at Worthy Farm in Somerset during the Glastonbury Festival in Britain, June 27, 2022. REUTERS/Dylan Martinez 

Volunteers clean up by the Pyramid stage at Worthy Farm in Somerset during the Glastonbury Festival in Britain, June 27, 2022. REUTERS/Dylan Martinez 

Volunteers clean up by the Pyramid stage at Worthy Farm in Somerset during the Glastonbury Festival in Britain, June 27, 2022. REUTERS/Dylan Martinez 

Volunteers clean up by the Pyramid stage at Worthy Farm in Somerset during the Glastonbury Festival in Britain, June 27, 2022. REUTERS/Dylan Martinez 

Volunteers clean up by the Pyramid stage at Worthy Farm in Somerset during the Glastonbury Festival in Britain, June 27, 2022. REUTERS/Dylan Martinez 

Volunteers clean up by the Pyramid stage at Worthy Farm in Somerset during the Glastonbury Festival in Britain, June 27, 2022. REUTERS/Dylan Martinez 

Volunteers clean up by the Pyramid stage at Worthy Farm in Somerset during the Glastonbury Festival in Britain, June 27, 2022. REUTERS/Dylan Martinez 

Volunteers clean up by the Pyramid stage at Worthy Farm in Somerset during the Glastonbury Festival in Britain, June 27, 2022. REUTERS/Dylan Martinez 

A volunteer applies hand sanitizer to a student before entering school to attend a class in person as the coronavirus disease (COVID-19) outbreak continues, in Ciudad Juarez, Mexico June 22, 2022. Picture taken June 22, 2022. REUTERS/Jose Luis Gonzalez 

Idrissa Joop, an health worker volunteer takes part in an awareness campaign against COVID-19 in Banjul, Gambia May 11, 2022. Picture taken May 11, 2022. REUTERS/Ngouda Dione 

Modou lamin Jammeh a volunteer talks with a woman as he takes part in an awareness campaign against COVID-19 in Banjul, Gambia May 11, 2022. Picture taken May 11, 2022. REUTERS/Ngouda Dione 

A volunteer chats with a resident after receiving a second booster shot of the coronavirus disease (COVID-19) vaccine in Waterford, Michigan, U.S., April 8, 2022. REUTERS/Emily Elconin 

Volunteers hold anti-epidemic bags as they deliver them to residents during the coronavirus disease (COVID-19) pandemic, in Hong Kong, China, April 3, 2022. REUTERS/Tyrone Siu 

A volunteer holds anti-epidemic bags as he delivers them to residents during the coronavirus disease (COVID-19) pandemic, in Hong Kong, China, April 3, 2022. REUTERS/Tyrone Siu 

Volunteers hold anti-epidemic bags as they deliver them to residents during the coronavirus disease (COVID-19) pandemic, in Hong Kong, China, April 3, 2022. REUTERS/Tyrone Siu 

Volunteers hold anti-epidemic bags as they deliver them to residents during the coronavirus disease (COVID-19) pandemic, in Hong Kong, China, April 3, 2022. REUTERS/Tyrone Siu 

A volunteer holds anti-epidemic bags as she delivers them to residents during the coronavirus disease (COVID-19) pandemic, in Hong Kong, China, April 3, 2022. REUTERS/Tyrone Siu 

A volunteer holds anti-epidemic bags as she delivers them to residents during the coronavirus disease (COVID-19) pandemic, in Hong Kong, China, April 2, 2022. REUTERS/Tyrone Siu 

A volunteer holds an anti-epidemic bag as he delivers them to residents during the coronavirus disease (COVID-19) pandemic, in Hong Kong, China, April 2, 2022. REUTERS/Tyrone Siu 

Volunteers from Hong Kong Dog Rescue take the dogs for a walk at Tai Po, in Hong Kong, China March 9, 2022. Picture taken March 9, 2022. REUTERS/Lam Yik 

Volunteers from Hong Kong Dog Rescue take the dogs for a walk at Tai Po, in Hong Kong, China March 9, 2022. Picture taken March 9, 2022. REUTERS/Lam Yik 

A medical volunteer prepares a syringe containing a dose of Comirnaty, the Pfizer-BioNTech vaccine against the coronavirus disease (COVID-19) at a vaccination center in St. Stephen's Cathedral, in Vienna, Austria February 5, 2022. REUTERS/Leonhard Foeger 

A medical volunteer prepares a syringe containing a dose of Comirnaty, the Pfizer-BioNTech vaccine against the coronavirus disease (COVID-19) at a vaccination center in St. Stephen's Cathedral, in Vienna, Austria February 5, 2022. REUTERS/Leonhard Foeger 

A medical volunteer prepares a syringe containing a dose of Comirnaty, the Pfizer-BioNTech vaccine against the coronavirus disease (COVID-19), at a vaccination center in St. Stephen's Cathedral, in Vienna, Austria February 5, 2022. REUTERS/Leonhard Foeger 

A volunteer prepares a syringe containing a dose of Comirnaty, the Pfizer-BioNTech vaccine against the coronavirus disease (COVID-19), at a vaccination center in St. Stephen's Cathedral, in Vienna, Austria February 5, 2022. REUTERS/Leonhard Foeger 

A medical volunteer prepares a syringe containing a dose of Comirnaty, the Pfizer-BioNTech vaccine against the coronavirus disease (COVID-19), at a vaccination center in St. Stephen's Cathedral, in Vienna, Austria February 5, 2022. REUTERS/Leonhard Foeger 

A volunteer wearing a protective mask and a face shield to prevent the spread of the coronavirus disease (COVID-19) stands in front of the Olympic rings signage at the Zhangjiakou Genting Snow Park ahead of the Beijing 2022 Winter Olympics in Zhangjiakou, China January 30, 2022. REUTERS/Lisi Niesner 

Chinese railway staff and a volunteer pictured at the entrance of Qinghe railway station inside a closed loop area designed to prevent the spread of the coronavirus disease (COVID-19) at high-speed trains to the mountain area ahead of the Beijing 2022 Winter Olympics in Beijing, China January 25, 2022. REUTERS/Fabrizio Bensch 

Chinese railway staff and volunteers pictured at the entrance of Qinghe railway station inside a closed loop area designed to prevent the spread of the coronavirus disease (COVID-19) at high-speed trains to the mountain area ahead of the Beijing 2022 Winter Olympics in Beijing, China January 25, 2022. REUTERS/Fabrizio Bensch 

Volunteer Julien Oppliger rests after receiving a new generation COVID-19 vaccine administered via an arm patch during a Phase I clinical study, led by Unisante at the University Hospital (CHUV) in Lausanne, Switzerland, January 19, 2022. REUTERS/Cecile Mantovani 

Monkeys are seen among the Hindu devotees and medical volunteers on the 272 steps of Sri Subramaniar Swamy Temple during celebrations of Thaipusam, which resumed with tight health protocols after a one-year hiatus due to the coronavirus disease (COVID-19) pandemic, at Batu Caves, Malaysia, January 18, 2022. REUTERS/Hasnoor Hussain TPX IMAGES OF THE DAY 

A volunteer guides locals arriving for vaccination against the coronavirus disease (COVID-19) at Prince Sultan Complex Health Center, in Riyadh, Saudi Arabia, January 13, 2022. REUTERS/Ahmed Yosri 

A volunteer in personal protective equipment (PPE) takes swab samples from a sex worker for a rapid antigen test amid the coronavirus disease (COVID-19) pandemic in Bangkok's Chinatown, Thailand, January 13, 2022. REUTERS/Athit Perawongmetha 

A volunteer in personal protective equipment (PPE) takes swab samples from a sex worker for a rapid antigen test amid the coronavirus disease (COVID-19) pandemic in Bangkok's Chinatown, Thailand, January 13, 2022. REUTERS/Athit Perawongmetha 

Volunteers in personal protective equipment (PPE) take swab samples from a homeless woman for a rapid antigen test amid the coronavirus disease (COVID-19) pandemic in Bangkok's Chinatown, Thailand, January 13, 2022. REUTERS/Athit Perawongmetha 

A volunteer in personal protective equipment (PPE) takes swab samples from a homeless man for a rapid antigen test amid the coronavirus disease (COVID-19) pandemic in Bangkok's Chinatown, Thailand, January 13, 2022. REUTERS/Athit Perawongmetha 

A volunteer in personal protective equipment (PPE) takes swab samples from a homeless man for a rapid antigen test amid the coronavirus disease (COVID-19) pandemic in Bangkok's Chinatown, Thailand, January 13, 2022. REUTERS/Athit Perawongmetha 

Volunteers stand in an entrance booth at the Main Media Center inside a closed loop area created to prevent the spread of the coronavirus disease (COVID-19) at the Beijing 2022 Winter Olympics, in Beijing, China, January 12, 2022. Picture taken January 12, 2022. REUTERS/Thomas Peter 

Volunteers and members of a disinfection team, wearing protective suits to protect from the coronavirus disease (COVID-19), gather at the Main Press Centre ahead of the Beijing 2022 Winter Olympics in Beijing, China January 12, 2022. REUTERS/Fabrizio Bensch 

A member of The People's Volunteer Corps (RELA) arranges vaccine cards at a clinic which administers booster doses of the coronavirus disease (COVID-19) vaccine in Subang Jaya, Malaysia, January 5, 2022. REUTERS/Hasnoor Hussain 

A volunteer burns a message during the National Good Riddance day ceremonial, amid the coronavirus disease (COVID-19) pandemic, in the Manhattan borough of New York City, New York, U.S., December 28, 2021. REUTERS/Jeenah Moon 

A volunteer stands at the entrance to a vaccination centre, amid the coronavirus disease (COVID-19) outbreak in Manchester, Britain, December 28, 2021. REUTERS/Phil Noble 

A volunteer stands at the entrance to a vaccination centre, amid the coronavirus disease (COVID-19) outbreak in Manchester, Britain, December 28, 2021. REUTERS/Phil Noble 

A volunteer looks over the observation area after patients receive a dose of the coronavirus disease (COVID-19) vaccine at Sparrow Laboratories Drive-Thru Services in Lansing, Michigan, U.S., December 27, 2021. REUTERS/Emily Elconin 

A Salvation Army volunteer Reynaldo Rivera plays bells for tip near the Rockefeller Center on Christmas Eve, as the Omicron coronavirus variant continues to spread, in the Manhattan borough of New York City, U.S., December 24, 2021. REUTERS/Jeenah Moon 

A volunteer distributes free toys during a Christmas holiday food pantry, where residents can also pick up pick up free groceries and home test kits for the coronavirus disease (COVID-19), at La Colaborativa, a non-profit social service organization, in Chelsea, Massachusetts, U.S., December 21, 2021. REUTERS/Brian Snyder 

A staff member uses a home coronavirus disease (COVID-19) test to check the heath of volunteers during the Christmas holiday food pantry at La Colaborativa, a non-profit social service organization, in Chelsea, Massachusetts, U.S., December 21, 2021. REUTERS/Brian Snyder 

A staff member uses a home coronavirus disease (COVID-19) test to check the heath of volunteers during the Christmas holiday food pantry at La Colaborativa, a non-profit social service organization, in Chelsea, Massachusetts, U.S., December 21, 2021. REUTERS/Brian Snyder 

A staff member uses home coronavirus disease (COVID-19) tests to check the heath of volunteers during the Christmas holiday food pantry at La Colaborativa, a non-profit social service organization, in Chelsea, Massachusetts, U.S., December 21, 2021. REUTERS/Brian Snyder 

A volunteer holds a sign requesting more vaccines at a coronavirus disease (COVID-19) pop-up vaccination centre at Wembley Stadium in London, Britain, December 19, 2021. REUTERS/Peter Nicholls 

Healthcare volunteers administer vaccines at a coronavirus disease (COVID-19) pop-up vaccination centre at Wembley Stadium in London, Britain, December 19, 2021. REUTERS/Peter Nicholls 

Healthcare volunteers administer vaccines at a coronavirus disease (COVID-19) pop-up vaccination centre at Wembley Stadium in London, Britain, December 19, 2021. REUTERS/Peter Nicholls 

A volunteer helps out inside a coronavirus disease (COVID-19) pop-up vaccination centre at Chelsea football ground, Stamford Bridge in London, Britain, December 18, 2021. REUTERS/David Klein