A medical worker prepares vials of the COVID-19 vaccines, Chinese Sinopharm, left, Sputnik V, center, and Pfizer at a vaccine centre, in the Usce shopping mall in Belgrade, Serbia, Thursday, May 6, 2021. Serbian authorities are looking for incentives for people to boost vaccination that has slowed down in recent weeks amid widespread anti-vaccination and conspiracy theories in the Balkan nation. The government has also promised a payment of around 25 euros to everyone who gets vaccinated by the end of May.