In this file picture, former US President Barack Obama speaks with Director of the National Institutes of Health Dr Francis Collins (L) in Bethesda, Maryland, September 30, 2009. Jim Watson/ AFP
Sheikh Mohamed bin Zayed, Crown Prince of Abu Dhabi and Deputy Supreme Commander of the Armed Forces (R) visits Emirates Field Hospital, at Emirates Humanitarian City, May 19. Seen with Sheikh Abdullah bin Mohammed Al Hamed, chairman of the Department of Health, Abu Dhabi. Hamad Al Mansoori / Ministry of Presidential Affairs
South Korean President Moon Jae-in at a ceremony marking the 40th anniversary of the pro-democracy Gwangju Uprising in Gwangju, May 18. Jung Yeon-je/ Reuters
Prime Minister of New Zealand Jacinda Ardern arrives for a Covid-19 update at Parliament on May 26, Wellington, New Zealand. Covid-19 Alert Level 2 restrictions will ease slightly from noon on May 29. Dom Thomas / Getty
German Chancellor Angela Merkel at a press conference in Berlin, May 20. Clemens Bilan/ Getty
Danish Prime Minister Mette Frederiksen has lunch at a cafe as part of her tour to different places in Jutland, eastern part of Denmark, as the country went into phase two of reopening, Denmark, May 18. Henning Bagger / Reuters
Graduating pupils Phoebe Seip, 18 (right), and her sister Sydney, 22, watch former US President Barack Obama deliver a virtual commencement address to millions of high school seniors who missed graduation ceremonies due to the coronavirus outbreak, in the US, May 16. Bing Guan / Reuters
In this file picture, former US President Barack Obama speaks with Director of the National Institutes of Health Dr Francis Collins (L) in Bethesda, Maryland, September 30, 2009. Jim Watson/ AFP
Sheikh Mohamed bin Zayed, Crown Prince of Abu Dhabi and Deputy Supreme Commander of the Armed Forces (R) visits Emirates Field Hospital, at Emirates Humanitarian City, May 19. Seen with Sheikh Abdullah bin Mohammed Al Hamed, chairman of the Department of Health, Abu Dhabi. Hamad Al Mansoori / Ministry of Presidential Affairs
South Korean President Moon Jae-in at a ceremony marking the 40th anniversary of the pro-democracy Gwangju Uprising in Gwangju, May 18. Jung Yeon-je/ Reuters
Prime Minister of New Zealand Jacinda Ardern arrives for a Covid-19 update at Parliament on May 26, Wellington, New Zealand. Covid-19 Alert Level 2 restrictions will ease slightly from noon on May 29. Dom Thomas / Getty
German Chancellor Angela Merkel at a press conference in Berlin, May 20. Clemens Bilan/ Getty
Danish Prime Minister Mette Frederiksen has lunch at a cafe as part of her tour to different places in Jutland, eastern part of Denmark, as the country went into phase two of reopening, Denmark, May 18. Henning Bagger / Reuters
Graduating pupils Phoebe Seip, 18 (right), and her sister Sydney, 22, watch former US President Barack Obama deliver a virtual commencement address to millions of high school seniors who missed graduation ceremonies due to the coronavirus outbreak, in the US, May 16. Bing Guan / Reuters
In this file picture, former US President Barack Obama speaks with Director of the National Institutes of Health Dr Francis Collins (L) in Bethesda, Maryland, September 30, 2009. Jim Watson/ AFP