Introduction: The top priority of active immunoprophylaxis of pertussis is immunisation of infants as they can develop severe multiple-organ complications or even die from this disease. Objectives: The aim of the work is the identification of factors negatively affecting vaccine immunity to pertussis in preschool children prior to the administration of the first booster. Patients and Methods: The research was conducted on 352 children from 4.5 to 5.9 years of age who were hospitalised in the University Children’s Hospital in Lublin (Poland) from 1 January 2012 to 31 December 2015. The children taking part in the study had been administered all the mandatory vaccines from their birth to the age of 2 or 2.5 years old according to the Polish Immunisation Program 2008-2009. The immunoenzymatic method ELISA was applied to assess vaccine immunity to tetanus, diphtheria, pertussis, Haemophilus influenzae type b (Hib), poliomyelitis (IPV), mumps, rubella and measles. The level of vaccine antibodies to hepatitis type B was determined chemilumiscently. Results: The protective antibody titer was not found in 41 (11.65%) children before the administration of the booster. To verify the collective impact of parameters analised on antibody titer to pertussis, the Generalized Linear Model (GLZ) was used. Gender, type of vaccine, asthma, Hib and mumps antibody titers have been shown to be predicators of vaccine immunity to pertussis. Conclusions: Immunomodulation considered on the example of titer of IgG antibody to pertussis can serve as a useful model of the assessment of development of acquired immunity after mandatory vaccinations.