1. National Reference Laboratory of Measles, Mumps, Rubella, Department of Virology, National Centre of Infectious and Parasitic Diseases (NCIPD), Sofia, Bulgaria
2. Unit of Epidemiology and Surveillance of Communicable Diseases, Department of Epidemiology, National Centre of Infectious and Parasitic Diseases (NCIPD), Sofia, Bulgaria
3. National Reference Laboratory of Cell Cultures, Rickettsia and Oncogenic Viruses, Department of Virology, National Centre of Infectious and Parasitic Diseases (NCIPD), Sofia, Bulgaria
4. Directorate of Protection of Public Health and Health Control, Ministry of Health, Sofia, Bulgaria