Medical University-Plovdiv;
Dept. Hygiene;
Ecology and Epidemiology;
Plovdiv;
Bulgaria;
Medical University-Plovdiv;
Dept. Infectious Diseases;
Parasitology and Tropical Medicine;
Plovdiv;
Bulgaria;
Vaccine; Preventable; Diseases; Measles; Mumps; Hepatitis; A; Outbreaks;