Abstract: Introduction. In the course of their work, medical workers are exposed to a biological factor, including bacterial, viral nature. Medical personnel come into contact with patients with measles, rubella, diphtheria, tuberculosis, hepatitis, coronavirus infection and other infectious diseases. The aim of the study is to assess the humoral immunity by the presence antibodies to the measles, rubella, hepatitis B viruses, to the causative agent COVID-19, tuberculosis and diphtheria bacteria in health care workers. Methods. Antibodies to measles, rubella, hepatitis B viruses, diphtheria and tetanus pathogens were measured in blood serum samples of 1221 MW; total antibodies to mycobacterium tuberculosis - in 120 MW; antibodies to the nucleocapsid protein of the SARS-CoV-2 virus – in 301 MW. The study was carried out by the method of enzyme immunoassay using commercial test systems; antibodies to diphtheria toxoid were detected in the passive hemagglutination reaction. The control group consisted of persons of engineering and technical personnel, comparable in age, gender and work experience. Results. Medical personnel were found to have significantly more frequent detection of seronegative reactions to the presence of antibodies to the hepatitis B virus (40.9% and 13.5%, p<0.001) of measles (28.8% and 3.9%, p<0.05); significantly high prevalence in the presence of total antibodies to mycobacterium tuberculosis (7.5% of cases in medical, 0% of cases of workers in the control group, p<0.05). In comparison with doctors, nurses had a significantly higher prevalence of antibodies to the nucleocapsid of the SARS-CoV-2 virus (38.9% and 23.7%, p<0.05). Conclusions. The study of post-vaccination immunity in medical workers showed the presence of a high proportion of seronegative individuals among vaccinated (viral hepatitis B, measles) medical workers and, accordingly, significant biological risks. A higher seroprevalence in total antibodies to Mycobacterium tuberculosis may also indicate insufficient immune protection among MW. The biological significance of seroprevalence to SARS-CoV-2 virus proteins (for nurses) requires further study.