ABSTRACT
The analysis of the morbidity and mortality rates in diphtheria, tetanus and pertussis in Bulgaria after the introduction of the compulsory mass immunization of children with combined DPT vaccine is presented. These data indicate that morbidity in diphtheria, tetanus and pertussis has sharply decreased. Favorable results with respect to these three diseases are the consequence of the complete coverage of the child population by immunization with the vaccine whose quality has been steadily improving for the last 20 years. A higher purity of toxoids has been achieved, and at present it exceeds the latest WHO requirements. Pertussis vaccine is produced with the use of strains whose serological characteristics correspond to those of the pertussis strains circulating in the country. The study of the reactogenicity of DPT vaccine, carried out over the period of 20 years, has shown that the vaccine has low reactogenicity.
