Abstract:

Pertussis is a highly contagious bacterial infection that affects the respiratory tract. The 
epidemiology of pertussis is highly variable and is influenced not only by the type of vaccine used, 
but also by the specific characteristics of the disease, the percentage of vaccine coverage, 
immunization schedules and the quality of surveillance. The aim of the study was to review the 
prevalence of pertussis in Bulgaria and to discuss the factors that influence its dynamics. Materials 
and methods: A retrospective analysis of epidemiological indicators of pertussis in Bulgaria was 
performed using the official database of the National Center for Infectious Parasitic Diseases-Sofia 
and the European Center for Disease Control. Results: Immunization against pertussis has been 
mandatory since 1957 and begins with an inactivated cell vaccine, included in the country's 
immunization calendar. Since 2010, the inactivated vaccine has been replaced by an acellular one 
as part of combined combined vaccines. The result of specific prophylaxis is a permanent reduction 
in morbidity, but periodic increases are associated with a decrease in the immunization coverage, 
weakening of post-vaccination immunity, the appearance of mild, difficult-to-diagnose clinical 
forms, as well as an increase in the role of adults as a source of infection. Conclusion: There is a 
permanent downward trend in the spread of pertussis in Bulgaria. The main moving mechanism of 
this trend is the implemented prophylaxis of the disease with a vaccine. The periodicity in the 
development of the epidemic process is preserved with a certain regularity. The factors influencing 
this periodicity are biological features of the bacterium and social factors that compromise the herd 
immunity of the population. 

Keywords: whooping cough, epidemiology, incidence, immunoprophylaxis

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