1. These authors contributed equally to this article and share first authorship
2. European Centre for Disease Prevention and Control (ECDC), Solna, Sweden
3. Ministry of Human Capacities, Budapest, Hungary
4. Department of Infectious Diseases, Istituto Superiore di Sanità (ISS), Rome, Italy
5. National Institute of Public Health, Bucharest, Romania
6. Hellenic Center for Disease Control & Prevention, Marousi, Greece
7. National Institute of Public Health “Dr Milan Jovanovic-Batut”, Belgrade, Serbia