People get registered to receive COVID-19 vaccines in Belgrade, Serbia on Jan. 25, 2021. After the arrival of the first million doses of the Chinese Sinopharm COVID-19 vaccine, Serbia started with mass vaccination on Jan. 19. (Photo by Nemanja Cabric/Xinhua)

People wait to receive COVID-19 vaccines in Belgrade, Serbia on Jan. 25, 2021. After the arrival of the first million doses of the Chinese Sinopharm COVID-19 vaccine, Serbia started with mass vaccination on Jan. 19. (Photo by Nemanja Cabric/Xinhua)

People wait to receive COVID-19 vaccines in Belgrade, Serbia on Jan. 25, 2021. After the arrival of the first million doses of the Chinese Sinopharm COVID-19 vaccine, Serbia started with mass vaccination on Jan. 19. (Photo by Nemanja Cabric/Xinhua)