The relevance of the research topic to medical psychology is determined by the lack of studies on the Russian samples of psychological factors of the decision-making about vaccination. According to our hypothesis one of such factors is the effect of psychological defense mechanisms. In the pilot study the parents were asked to describe the situations when they seek pediatric care. Based on the results three groups of situations not involving decision-making on vaccination were described. The difficulties of actualization of the parents' experience were documented. This is why the descriptions of 10 situations, developed by the authors following the discussion of vaccination on the parents' online forum, were used in the main research. The content of the situations developed by the authors comprised various decisions, consequences of vaccination, and emotional coloring of the situation. The subjects' responses were recorded in a structured interview. The sample was formed on the basis of a voluntary informed consent obtained from 76 mothers of children under the age of 1 year, who brought their children to the ambulatory pediatric clinics of Yaroslavl during immunizations period. In total 382 responses were obtained. The participants could give three variants of answers: an abstract one (for example: "I am a supporter of vaccinations"), in the third person (for example: "this mom should not have given her consent to vaccination"); in the first person (for example: "in such situation I would give my consent"). The research data have allowed to describe the psychological defense tension as decision-making factor. The psychological defense tension was evaluated by the divergence between three variant of answers in one situation. All the cases were divided into two groups depending on the psychological defense tension. In all three variants of answers participants more often refuse to have their children vaccinated in situations with relatively high tension of psychological defense compared with the situations characterized by low tensions. Psychological defense tension was marked for practical application of the obtained results. The closest analogue of the tension is the hygiene factors described by F. Herzberg. We assume that the tension of psychological defense is caused not only by the content of the situation, but by the presence in the description of the situation of specific lexical markers: hepatitis B, vomiting, rotavirus, etc. In the situations descriptions that do not induce the intensity of the defense activity such markers are less common. Additional research will be conducted to check this assumption. Creation of awareness among parents can be more effective taking into account factors of psychological defense activation. The research leads to the conclusion that activation of the psychological defense mechanisms in a situation of decision-making about vaccination is one of the factors associated with denial of vaccination.
