A health worker applies a dose of the AstraZeneca vaccine during the first day of a three-day COVID-19 vaccination campaign for people over age 35 in the Complexo da Maré favela of Rio de Janeiro, Brazil, Brazil, Thursday, July 29, 2021. Some recipients will be monitored to study the rate of protection the vaccines provide and the extent to which virus variants are circulating. (Photo by Bruna Prado/AP Photo)

A brown bear cub by the Khailyulya River in north-east Kamchatka, Russia on July 24, 2021. (Photo by Yuri Smityuk/TASS)

A couple pours water on their dogs during a hot day, in Rome, Thursday, August 12, 2021. In Italy, 15 cities received warnings from the health ministry about high temperatures and humidity with peaks predicted for Friday. The cities included Rome, Florence and Palermo, but also Bolzano, which is usually a refreshing hot-weather escape in the Alps. (Photo by Andrew Medichini/AP Photo)

Olympic medal winning twins Jessica (left) and Jennifer Gadirova celebrate their GCSE results at Aylesbury Vale Academy in Buckinghamshire, United Kingdom onThursday, August 12, 2021. (Photo by Steve Parsons/PA Images via Getty Images)

Wounded women arrive at a hospital for treatment after two blasts, which killed at least five and wounded a dozen, outside the airport in Kabul on August 26, 2021. (Photo by Wakil Kohsar/AFP Photo)

Beatriz Hatz of the United States competes in the women's T62 long jump final during the 2020 Paralympics at the National Stadium in Tokyo, Saturday, August 28, 2021. (Photo by Kiichiro Sato/AP Photo)

Astronauts Nie Haisheng (C), Liu Boming (R) and Tang Hongbo are out of the return capsule of the Shenzhou-12 spaceship at the Dongfeng landing site in north China's Inner Mongolia Autonomous Region on September 17, 2021. Three Chinese astronauts, the first sent to orbit for space station construction, have completed their three-month mission and returned to Earth safely on Friday. Photo by Lian Zhen/Xinhua News Agency)

A giant panda named Kai Kai looks on as he opens a gift to celebrate his upcoming 14th birthday at the River Safari wildlife park in Singapore on September 10, 2021. (Photo by Roslan Rahman/AFP Photo)