Seven-year-old Mimi Meade winces from the sting as Dr. Richard Mulvaney inoculates her April 26, 1954 in McClean, Va., with the new Salk polio vaccine. Mrs. John Lucas, a registered nurse, holds Mimi's arm steady as she gets one of the first injections of the countrywide test. (Photo by Harvey Georges/AP Photo)

A veterinarian from the zoo of Besancon feeds “Soa”, a female crowned sifaka, in Besancon, eastern France, on February 18, 2019. The crowned sifaka is a critically endangered species from Madagascar. There were only 6 females over 20 individuals living in 7 zoos worldwide end of 2018. (Photo by Sébastien Bozon/AFP Photo)

A fan gestures next to a police officer while celebrating the life of British singer Keith Flint of techno group “The Prodigy” after his funeral in Braintree, Essex, Britain, March 29, 2019. (Photo by Henry Nicholls/Reuters)

Two models pose backstage before presenting the collection of Chinese designer Zhang Peng during the China Fashion Week in Beijing on March 29, 2019. (Photo by Fred Dufour/AFP Photo)

Sudanese protesters rally outside the army complex in Sudan's capital Khartoum on April 18, 2019. Huge crowds of protesters thronged the Sudanese capital Khartoum today, a week after the army's ouster of president Omar al-Bashir, determined to complete their revolution seeking civilian rule. (Photo by Ozan Kose/AFP Photo)

A drag queen goes through security a RuPaul’s DragCon in Los Angeles, USA on May 26, 2019. (Photo by Ronen Tivony/SOPA Images/Rex Features/Shutterstock)

Over 30 Douglas C-47 Skytrains (Dakotas) making final preparations for flight formation practice before the 75th D-Day Anniversary flight to Normandy in Duxford, England on June 4, 2019. (Photo by UK Air Force Images)

Yan Mengjie sits on a boat as she poses for photos near Erhai Lake in Dali Bai Autonomous Prefecture, Yunnan province, China on June 16, 2019. Erhai is one of China's biggest freshwater lakes and a backdrop to the city of Dali, which drew 47 million visitors last year, more than triple the number in 2010. Hotels and homestays have sprung up along a 31-mile (50-km) stretch of lakeside road to accommodate tourists. But officials ordered some hotels demolished after President Xi Jinping during a 2015 visit called for the lake to be protected. (Photo by Tingshu Wang/Reuters)