There is currently an increasing interest in the development of new-generation purified antigen-based vaccines with a higher safety profile compared to conventional inactivated vaccines. The main problem of subunit vaccines is their lower immunogenicity compared to whole-cell vaccines and inducing weaker and shorter-lasting immune responses. In this paper, the results of the assay of the potency of the tetanus component combined with the diphtheria component and whole-cell pertussis vaccine (DTwP), diphtheria and tetanus vaccine (DT), and in monovalent tetanus vaccine (T) are presented. In the mice model, an adjuvant impact of the whole-cell pertussis component on the immune response against tetanus was observed. It was noticed that the potency of tetanus component in the DTwP vaccine was significantly higher than tetanus potency in DT and T vaccines, despite the same bounding ability unit of the tetanus toxoid in the vaccine formulations. The levels of induction of tetanus antibodies by the tested vaccines were also examined. There were no differences in the induction of humoral responses against tetanus by tested vaccines. This publication discusses the possible mechanisms of impact of the whole-cell pertussis component on the other vaccine antigens and the positive and negative aspects of using the whole-cell pertussis component as an adjuvant.