Britain's Prime Minister Boris Johnson, wearing a hair net and face covering views the last minute quality testing of the 'fill and finish' stage of the manufacturing process of COVID-19 vaccines, during his visit to Wockhardt's pharmaceutical manufacturing facility in Wrexham, Wales, Britain November 30, 2020. Paul Ellis/Pool via REUTERS

Britain's Prime Minister Boris Johnson, wearing a hair net and face covering views the last minute quality testing of the 'fill and finish' stage of the manufacturing process of COVID-19 vaccines, during his visit to Wockhardt's pharmaceutical manufacturing facility in Wrexham, Wales, Britain November 30, 2020. Paul Ellis/Pool via REUTERS

Britain's Prime Minister Boris Johnson, wearing a hair net and face covering views the last minute quality testing of the 'fill and finish' stage of the manufacturing process of COVID-19 vaccines, during his visit to Wockhardt's pharmaceutical manufacturing facility in Wrexham, Wales, Britain November 30, 2020. Paul Ellis/Pool via REUTERS

Britain's Prime Minister Boris Johnson, wearing a hair net and face covering views the last minute quality testing of the 'fill and finish' stage of the manufacturing process of COVID-19 vaccines, during his visit to Wockhardt's pharmaceutical manufacturing facility in Wrexham, Wales, Britain November 30, 2020. Paul Ellis/Pool via REUTERS

Britain's Prime Minister Boris Johnson, wearing a hair net and face covering gestures as he views the last minute quality testing of the 'fill and finish' stage of the manufacturing process of COVID-19 vaccines, during his visit to Wockhardt's pharmaceutical manufacturing facility in Wrexham, Wales, Britain November 30, 2020. Paul Ellis/Pool via REUTERS

Britain's Prime Minister Boris Johnson, wearing a hair net and face covering views the last minute quality testing of the 'fill and finish' stage of the manufacturing process of COVID-19 vaccines, during his visit to Wockhardt's pharmaceutical manufacturing facility in Wrexham, Wales, Britain November 30, 2020. Paul Ellis/Pool via REUTERS

Britain's Prime Minister Boris Johnson, wearing a hair net and face covering views the last minute quality testing of the 'fill and finish' stage of the manufacturing process of COVID-19 vaccines, during his visit to Wockhardt's pharmaceutical manufacturing facility in Wrexham, Wales, Britain November 30, 2020. Paul Ellis/Pool via REUTERS

Britain's Prime Minister Boris Johnson, wearing a hair net and face covering views the last minute quality testing of the 'fill and finish' stage of the manufacturing process of COVID-19 vaccines, during his visit to Wockhardt's pharmaceutical manufacturing facility in Wrexham, Wales, Britain November 30, 2020. Paul Ellis/Pool via REUTERS

Britain's Prime Minister Boris Johnson, wearing a hair net and face covering, poses for a photograph with a vial as he views the last minute quality testing of the 'fill and finish' stage of the manufacturing process of COVID-19 vaccines, during his visit to Wockhardt's pharmaceutical manufacturing facility in Wrexham, Wales, Britain November 30, 2020. Paul Ellis/Pool via REUTERS

Britain's Prime Minister Boris Johnson, wearing a hair net and face covering reacts as he views the last minute quality testing of the 'fill and finish' stage of the manufacturing process of COVID-19 vaccines, during his visit to Wockhardt's pharmaceutical manufacturing facility in Wrexham, Wales, Britain November 30, 2020. Paul Ellis/Pool via REUTERS

Britain's Prime Minister Boris Johnson, wearing a hair net and face covering reacts as he views the last minute quality testing of the 'fill and finish' stage of the manufacturing process of COVID-19 vaccines, during his visit to Wockhardt's pharmaceutical manufacturing facility in Wrexham, Wales, Britain November 30, 2020. Paul Ellis/Pool via REUTERS

Britain's Prime Minister Boris Johnson, wearing a hair net and face covering reacts as he views the last minute quality testing of the 'fill and finish' stage of the manufacturing process of COVID-19 vaccines, during his visit to Wockhardt's pharmaceutical manufacturing facility in Wrexham, Wales, Britain November 30, 2020. Paul Ellis/Pool via REUTERS

Abdelrahman Tarek, 11-year-old cancer patient is seen on a stage before practicing traditional Tanoura dance to keep his spirits high as he battles the harsh illness at a small theatre in central Cairo, Egypt November 21, 2020. Picture taken November 21, 2020. REUTERS/Mohamed Abd El Ghany

Thai protesters stage inflatable duck parade in Nonthaburi on the outskirts of Bangkok, Thailand November 28, 2020. REUTERS/Matthew Tostevin

Thai protesters stage inflatable duck parade in Nonthaburi on the outskirts of Bangkok, Thailand November 28, 2020. REUTERS/Matthew Tostevin

Lebanese artist, who goes by the stage-name "Blu Fiefer", attends an interview with Reuters at her home, in Qlayaat, Lebanon November 19, 2020. Picture taken November 19, 2020. REUTERS/Emma Freiha

Lebanese artist, who goes by the stage-name "Blu Fiefer", attends an interview with Reuters at her home, in Qlayaat, Lebanon November 19, 2020. Picture taken November 19, 2020. REUTERS/Emma Freiha

Lebanese artist, who goes by the stage-name "Blu Fiefer", works on a laptop during an interview with Reuters at her home, in Qlayaat, Lebanon November 19, 2020. Picture taken November 19, 2020. REUTERS/Emma Freiha

Animal rights activists from the People for the Ethical Treatment of Animals (PETA), dressed as "chained monkeys", stage a protest against what they say is monkey abuse in Thailand's coconut industry following PETA's investigation, outside the Royal Thai Embassy in Makati City, Metro Manila, Philippines, November 25, 2020. REUTERS/Eloisa Lopez

Animal rights activists from the People for the Ethical Treatment of Animals (PETA), dressed as "chained monkeys", stage a protest against what they say is monkey abuse in Thailand's coconut industry following PETA's investigation, outside the Royal Thai Embassy in Makati City, Metro Manila, Philippines, November 25, 2020. REUTERS/Eloisa Lopez TPX IMAGES OF THE DAY

Animal rights activists from the People for the Ethical Treatment of Animals (PETA), dressed as "chained monkeys", stage a protest against what they say is monkey abuse in Thailand's coconut industry following PETA's investigation, outside the Royal Thai Embassy in Makati City, Metro Manila, Philippines, November 25, 2020. REUTERS/Eloisa Lopez

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Russia's Daniil Medvedev is interviewed as he celebrates winning his group stage match against Argentina's Diego Schwartzman REUTERS/Toby Melville

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Russia's Daniil Medvedev is interviewed as he celebrates winning his group stage match against Argentina's Diego Schwartzman REUTERS/Toby Melville

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Russia's Daniil Medvedev celebrates winning his group stage match against Argentina's Diego Schwartzman REUTERS/Toby Melville

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Russia's Daniil Medvedev celebrates winning his group stage match against Argentina's Diego Schwartzman REUTERS/Toby Melville

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Russia's Daniil Medvedev shakes hands with Argentina's Diego Schwartzman as he celebrates winning their group stage match REUTERS/Toby Melville

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Russia's Daniil Medvedev in action during his group stage match against Argentina's Diego Schwartzman REUTERS/Toby Melville

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Russia's Daniil Medvedev in action during his group stage match against Argentina's Diego Schwartzman REUTERS/Toby Melville

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Russia's Daniil Medvedev in action during his group stage match against Argentina's Diego Schwartzman REUTERS/Toby Melville

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Russia's Daniil Medvedev in action during his group stage match against Argentina's Diego Schwartzman REUTERS/Toby Melville

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Argentina's Diego Schwartzman in action during his group stage match against Russia's Daniil Medvedev REUTERS/Toby Melville

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Argentina's Diego Schwartzman reacts during his group stage match against Russia's Daniil Medvedev REUTERS/Toby Melville

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Argentina's Diego Schwartzman in action during his group stage match against Russia's Daniil Medvedev REUTERS/Toby Melville

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Russia's Daniil Medvedev in action during his group stage match against Argentina's Diego Schwartzman REUTERS/Toby Melville

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Russia's Daniil Medvedev in action during his group stage match against Argentina's Diego Schwartzman REUTERS/Toby Melville

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Argentina's Diego Schwartzman during the warm up before his group stage match against Russia's Daniil Medvedev REUTERS/Toby Melville

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Argentina's Diego Schwartzman before his group stage match against Russia's Daniil Medvedev REUTERS/Toby Melville

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Russia's Daniil Medvedev before his group stage match against Argentina's Diego Schwartzman REUTERS/Toby Melville

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Russia's Daniil Medvedev arrives before his group stage match against Argentina's Diego Sebastian Schwartzman REUTERS/Toby Melville

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Serbia's Novak Djokovic after winning his group stage match against Germany's Alexander Zverev Action Images via Reuters/Paul Childs

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Serbia's Novak Djokovic celebrates winning his group stage match against Germany's Alexander Zverev Action Images via Reuters/Paul Childs

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Serbia's Novak Djokovic after winning his group stage match against Germany's Alexander Zverev REUTERS/Toby Melville

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Serbia's Novak Djokovic celebrates winning his group stage match against Germany's Alexander Zverev REUTERS/Toby Melville

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Serbia's Novak Djokovic after winning his group stage match against Germany's Alexander Zverev Action Images via Reuters/Paul Childs

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Serbia's Novak Djokovic celebrates winning his group stage match against Germany's Alexander Zverev Action Images via Reuters/Paul Childs

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Germany's Alexander Zverev after losing his group stage match against Serbia's Novak Djokovic REUTERS/Toby Melville

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Germany's Alexander Zverev after losing his group stage match against Serbia's Novak Djokovic REUTERS/Toby Melville

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Serbia's Novak Djokovic celebrates during his group stage match against Germany's Alexander Zverev REUTERS/Toby Melville

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Serbia's Novak Djokovic celebrates winning his group stage match against Germany's Alexander Zverev REUTERS/Toby Melville

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Serbia's Novak Djokovic celebrates winning his group stage match against Germany's Alexander Zverev REUTERS/Toby Melville

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Serbia's Novak Djokovic in action during his group stage match against Germany's Alexander Zverev Action Images via Reuters/Paul Childs

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Serbia's Novak Djokovic celebrates winning his group stage match against Germany's Alexander Zverev REUTERS/Toby Melville

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Serbia's Novak Djokovic after winning his group stage match against Germany's Alexander Zverev Action Images via Reuters/Paul Childs

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Serbia's Novak Djokovic celebrates winning his group stage match against Germany's Alexander Zverev Action Images via Reuters/Paul Childs

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Serbia's Novak Djokovic after winning his group stage match against Germany's Alexander Zverev Action Images via Reuters/Paul Childs

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Serbia's Novak Djokovic celebrates winning his group stage match against Germany's Alexander Zverev Action Images via Reuters/Paul Childs

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Serbia's Novak Djokovic celebrates winning his group stage match against Germany's Alexander Zverev Action Images via Reuters/Paul Childs

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Serbia's Novak Djokovic celebrates winning his group stage match against Germany's Alexander Zverev Action Images via Reuters/Paul Childs TPX IMAGES OF THE DAY

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Serbia's Novak Djokovic celebrates winning his group stage match against Germany's Alexander Zverev Action Images via Reuters/Paul Childs

Tennis - ATP Finals - The O2, London, Britain - November 20, 2020 Serbia's Novak Djokovic celebrates winning his group stage match against Germany's Alexander Zverev Action Images via Reuters/Paul Childs