Good for Serbia for implementing some centralized system. A PCR test result in the U.S has absolutely no way of being verified, either negative or positive In Israel, which swabs every person who lands at the airport. There is a suspiciously steady stream of people flying in from the U.S who were negative before take off and positive 10 minutes after landing
https://ec.europa.eu/info/live-work-travel-eu/coronavirus-re...