A healthcare worker in personal protective equipment (PPE) collects a swab sample from a resident during a testing campaign for the coronavirus disease (COVID-19), in Mumbai, India, February 23, 2021. REUTERS/Francis Mascarenhas

A healthcare worker in personal protective equipment (PPE) collects a swab sample from a resident during a testing campaign for the coronavirus disease (COVID-19), in Mumbai, India, February 23, 2021. REUTERS/Francis Mascarenhas

A man has a swab sample taken for a coronavirus disease (COVID-19) antigen test, at a temporary site for massive testing at a fronton (court wall) in Pedrezuela, Spain, February 22, 2021. REUTERS/Sergio Perez

A woman has a swab sample taken for a coronavirus disease (COVID-19) antigen test, at a temporary site for massive testing at a fronton (court wall) in Pedrezuela, Spain, February 22, 2021. REUTERS/Sergio Perez

A man has a swab sample taken for a coronavirus disease (COVID-19) antigen test, at a temporary site for massive testing at a fronton (court wall) in Pedrezuela, Spain, February 22, 2021. REUTERS/Sergio Perez

A woman has a swab sample taken for a coronavirus disease (COVID-19) antigen test, at a temporary site for massive testing at a fronton (court wall) in Pedrezuela, Spain, February 22, 2021. REUTERS/Sergio Perez

A man has a swab sample taken for a coronavirus disease (COVID-19) antigen test, at a temporary site for massive testing at a fronton (court wall) in Pedrezuela, Spain, February 22, 2021. REUTERS/Sergio Perez

A man has a swab sample taken for a coronavirus disease (COVID-19) antigen test, at a temporary site for massive testing at a fronton (court wall) in Pedrezuela, Spain, February 22, 2021. REUTERS/Sergio Perez

A healthcare worker collects a swab sample from a passenger during a rapid antigen testing campaign for the coronavirus disease (COVID-19), at a railway station in Mumbai, India, February 22, 2021. REUTERS/Niharika Kulkarni

A healthcare worker wearing personal protective equipment (PPE) takes a swab sample from a woman for the coronavirus disease (COVID-19) test in Cantagallo, an indigenous Shipibo-Conibo community, during the vaccination campaign against the coronavirus, in Lima, Peru February 19, 2021. REUTERS/Angela Ponce

A healthcare worker wearing personal protective equipment (PPE) takes a swab sample from a woman for the coronavirus disease (COVID-19) test in Cantagallo, an indigenous Shipibo-Conibo community, during the vaccination campaign against the coronavirus, in Lima, Peru February 19, 2021. REUTERS/Angela Ponce

A healthcare worker wearing personal protective equipment (PPE) takes a swab sample from a woman for the coronavirus disease (COVID-19) in Cantagallo, an indigenous Shipibo-Conibo community, during the vaccination campaign against the coronavirus, in Lima, Peru February 19, 2021. REUTERS/Angela Ponce

A healthcare worker wearing personal protective equipment (PPE) takes a swab sample from a woman for the coronavirus disease (COVID-19) in Cantagallo, an indigenous Shipibo-Conibo community, during the vaccination campaign against the coronavirus, in Lima, Peru February 19, 2021. REUTERS/Angela Ponce

A medical worker works on a sample after administering a nasal swab to a patient at a coronavirus disease (COVID-19) testing centre installed inside in the Kursaal concert hall in Dunkirk, France, February 18, 2021. REUTERS/Pascal Rossignol

A woman reacts as a health worker uses a swab to collect a sample at a makeshift community testing centre for the coronavirus disease (COVID-19), in Hong Kong, China February 17, 2021. REUTERS/Tyrone Siu

A woman reacts as a health worker uses a swab to collect a sample at a makeshift community testing centre for the coronavirus disease (COVID-19), in Hong Kong, China February 17, 2021. REUTERS/Tyrone Siu

A woman has a swab sample taken for the coronavirus disease (COVID-19) antigen test at a temporary site at the sport pavilion in Serranillos del Valle, Spain, February 16, 2021. REUTERS/Sergio Perez

A woman has a swab sample taken for the coronavirus disease (COVID-19) antigen test at a temporary site at the sport pavilion in Serranillos del Valle, Spain, February 16, 2021. REUTERS/Sergio Perez

A man has a swab sample taken for the coronavirus disease (COVID-19) antigen test at a temporary site at the sport pavilion in Serranillos del Valle, Spain, February 16, 2021. REUTERS/Sergio Perez

A man has a swab sample taken for the coronavirus disease (COVID-19) antigen test at a temporary site at the sport pavilion in Serranillos del Valle, Spain, February 16, 2021. REUTERS/Sergio Perez

Medical workers collect a swab sample from a man to be tested for the coronavirus disease (COVID-19) at Kuala Lumpur Hospital in Kuala Lumpur, Malaysia February 16, 2021. REUTERS/Lim Huey Teng

Medical workers collect a swab sample from a woman to be tested for the coronavirus disease (COVID-19) at Kuala Lumpur Hospital in Kuala Lumpur, Malaysia February 16, 2021. REUTERS/Lim Huey Teng

A health care worker takes a swab sample from a man to test for the coronavirus disease (COVID-19), at a COVID-19 mobile testing site at Heathrow Airport, in London, Britain, February 15, 2021. REUTERS/Hannah McKay

A medical team member takes a swab sample from a man to be tested for the coronavirus disease (COVID-19), at a medical center in a hospital in the holy city of Najaf, Iraq February 15, 2021. REUTERS/Alaa al-Marjani

A medical team member takes a swab sample from a man to be tested for the coronavirus disease (COVID-19), at a medical center in a hospital in the holy city of Najaf, Iraq February 15, 2021. REUTERS/Alaa al-Marjani

A medical team member wearing a protective suit and a face mask, works on blood samples to be tested for coronavirus disease (COVID-19), at a medical center in a hospital in the holy city of Najaf, Iraq February 15, 2021. REUTERS/Alaa al-Marjani

A medical team member wearing a protective suit and a face mask, works on blood samples to be tested for coronavirus disease (COVID-19), at a medical center in a hospital in the holy city of Najaf, Iraq February 15, 2021. REUTERS/Alaa al-Marjani

A view of blood samples to be tested for the coronavirus disease (COVID-19) are pictured at a medical center of a hospital in the holy city of Najaf, Iraq February 15, 2021. REUTERS/Alaa al-Marjani

A health worker prepares to take test sample at a drive-thru coronavirus disease (COVID-19) testing site at the FITTEAM Ballpark parking lot in West Palm Beach, Florida, February 9, 2021. Picture taken February 9, 2021. REUTERS/Shannon Stapleton

A health worker prepares to take test sample at a drive-thru coronavirus disease (COVID-19) testing site at the FITTEAM Ballpark parking lot in West Palm Beach, Florida, February 9, 2021. Picture taken February 9, 2021. REUTERS/Shannon Stapleton

A health worker prepares to take test sample at a drive-thru coronavirus disease (COVID-19) testing site at the FITTEAM Ballpark parking lot in West Palm Beach, Florida, February 9, 2021. Picture taken February 9, 2021. REUTERS/Shannon Stapleton

A military dog sniffs a urine sample during a demonstration to detect the coronavirus disease (COVID-19), at an army veterinary hospital in New Delhi, India, February 9, 2021. REUTERS/Adnan Abidi

A military dog sniffs urine samples during a demonstration to detect the coronavirus disease (COVID-19), at an army veterinary hospital in New Delhi, India, February 9, 2021. REUTERS/Adnan Abidi

An army soldier wearing personal protective equipment (PPE) walks a military dog to check sweat samples during a demonstration to detect the coronavirus disease (COVID-19), at an army veterinary hospital in New Delhi, India, February 9, 2021. REUTERS/Adnan Abidi

An elderly woman leaves after taking her swab sample, at a minibus that was converted into a COVID-19 mobile test centre for people who can't get to regular test centres, amid the spread of the coronavirus disease (COVID-19), in Walsall, Britain, February 8, 2021. REUTERS/Carl Recine

A healthcare worker indicates an elderly woman how to take her swab sample, at a minibus that was converted into a COVID-19 mobile test centre for people who can't get to regular test centres, amid the spread of the coronavirus disease (COVID-19), in Walsall, Britain, February 8, 2021. REUTERS/Carl Recine

A healthcare worker indicates an elderly woman how to take her swab sample, at a minibus that was converted into a COVID-19 mobile test centre for people who can't get to regular test centres, amid the spread of the coronavirus disease (COVID-19), in Walsall, Britain, February 8, 2021. REUTERS/Carl Recine

A healthcare worker indicates an elderly woman how to take her swab sample, at a minibus that was converted into a COVID-19 mobile test centre for people who can't get to regular test centres, amid the spread of the coronavirus disease (COVID-19), in Walsall, Britain, February 8, 2021. REUTERS/Carl Recine

A healthcare worker indicates an elderly woman how to take her swab sample, at a minibus that was converted into a COVID-19 mobile test centre for people who can't get to regular test centres, amid the spread of the coronavirus disease (COVID-19), in Walsall, Britain, February 8, 2021. REUTERS/Carl Recine

Medical team member takes a DNA blood sample from a woman from the Yazidi religious minority looking for a relative missing after the August 2014 Islamic State militant attack in Kojo, Iraq February 7, 2021. REUTERS/Thaier al-Sudani

Medical team member takes a DNA blood sample from a woman from the Yazidi religious minority looking for a relative missing after the August 2014 Islamic State militant attack in Kojo, Iraq February 7, 2021. REUTERS/Thaier al-Sudani

Medical team member takes a DNA blood sample from a woman from the Yazidi religious minority looking for a relative missing after the August 2014 Islamic State militant attack in Kojo, Iraq February 7, 2021. REUTERS/Thaier al-Sudani

People wait before a healthcare worker takes a sample for the COVID-19 rapid antigen testing, at the Iztapalapa neighbourhood in Mexico City, Mexico, February 5, 2021. REUTERS/Henry Romero

A healthcare worker wearing personal protective equipment (PPE) takes a swab sample from a man for the coronavirus disease (COVID-19) rapid antigen testing at the Iztapalapa neighbourhood in Mexico City, Mexico, February 5, 2021. REUTERS/Henry Romero

A healthcare worker wearing personal protective equipment (PPE) takes a swab sample from a woman, for the coronavirus disease (COVID-19) rapid antigen testing, at the Iztapalapa neighbourhood in Mexico City, Mexico February 5, 2021. REUTERS/Henry Romero

A mock sample of a QR-coded vaccination pass that will be distributed to all people that receive the vaccine against the coronavirus disease (COVID-19) is pictured in the eastern Bavarian district of Altoetting, Germany February 5, 2021. REUTERS/Marcus Nagle

A mock sample of a QR-coded vaccination pass that will be distributed to all people that receive the vaccine against the coronavirus disease (COVID-19) is pictured in the eastern Bavarian district of Altoetting, Germany February 5, 2021. REUTERS/Marcus Nagle

A mock sample of a QR-coded vaccination pass that will be distributed to all people that receive the vaccine against the coronavirus disease (COVID-19) is pictured in the eastern Bavarian district of Altoetting, Germany February 5, 2021. REUTERS/Marcus Nagle

A woman gives a swab sample at a mobile self-testing centre, amid the outbreak of the coronavirus disease (COVID-19) in Pollards Hill, London, Britain February 5, 2021. REUTERS/Henry Nicholls

People give swab samples at a mobile self-testing centre, amid the outbreak of the coronavirus disease (COVID-19) in Pollards Hill, London, Britain February 5, 2021. REUTERS/Henry Nicholls

A nurse carries glasses with samples of breast milk for babies infected with the coronavirus disease (COVID-19), at the coronavirus neo-natal unit of the Maternal Perinatal Hospital 'Monica Pretelini Saenz', in Toluca, Mexico February 4, 2021. REUTERS/Luis Cortes TPX IMAGES OF THE DAY

A healthcare worker wearing personal protective equipment (PPE) collects a swab sample from a man during a rapid antigen testing campaign for the coronavirus disease (COVID-19), at a kiosk in Ahmedabad, India, February 4, 2021. REUTERS/Amit Dave

A man wearing a protective mask gives a plastic bag containing his air-sample to be tested using GeNose C19 (GeNose), a coronavirus disease (COVID-19) detection tool, at a train station in Jakarta, Indonesia, February 3, 2021. REUTERS/Ajeng Dinar Ulfiana

A healthcare worker holds a plastic bag containing a commuter's air-sample to be tested for the coronavirus disease (COVID-19) using GeNose C19 (GeNose), a COVID-19 detection tool, at a train station in Jakarta, Indonesia, February 3, 2021. REUTERS/Ajeng Dinar Ulfiana

A woman wearing a protective mask blows a plastic bag as she takes her air-sample to be tested for the coronavirus disease (COVID-19) using GeNose C19 (GeNose), a COVID-19 detection tool, at a train station in Jakarta, Indonesia, February 3, 2021. REUTERS/Ajeng Dinar Ulfiana

Commuters wearing protective masks blow a plastic bag as they take their air-sample to be tested using GeNose C19 (GeNose), a coronavirus disease (COVID-19) detection tool, at a train station in Jakarta, Indonesia, February 3, 2021. REUTERS/Ajeng Dinar Ulfiana

Commuters wearing protective masks hold plastic bags containing their air-samples to be tested using GeNose C19 (GeNose), a coronavirus disease (COVID-19) detection tool, at a train station in Jakarta, Indonesia, February 3, 2021. REUTERS/Ajeng Dinar Ulfiana

A healthcare worker tests an air-sample of a commuter using GeNose C19 (GeNose), a coronavirus disease (COVID-19) detection tool, at a train station in Jakarta, Indonesia, February 3, 2021. REUTERS/Ajeng Dinar Ulfiana

A healthcare worker in protective equipment holds a swab sample at a rapid antigen mass testing station, as the spread of the coronavirus disease (COVID-19) continues, in Vienna, Austria, February 3, 2021. REUTERS/Leonhard Foeger