1 Directorate of Research, Studies, and Documentation, National Public Health Organization, Athens, Greece. Electronic address: maltezou.helena@gmail.com.
2 Department of Epidemiology, Faculty of Medicine, University of Novi Sad, Novi Sad, Serbia; Center for Disease Control and Prevention, Institute of Public Health of Vojvodina, Novi Sad, Serbia.
3 Pediatric Department, Democritus University of Thrace, Alexandroupolis, Greece.
4 Directorate of Research, Studies, and Documentation, National Public Health Organization, Athens, Greece.
5 Mayo Vaccine Research Group, Mayo Clinic and Foundation, Rochester, MN, United States.