Vaccine hesitancy is considered by the World Health Organization as one of the global threats to human health. The vaccine hesitancy is closely connected to the problems of online communication. A lot of comments on social networks are devoted to the properties of the COVID-19 vaccine, discussions of doubts about the safety of vaccination and its necessity, which is one of the manifestations of the phenomenon of vaccine indecision. Understanding the current discourse of vaccine hesitancy requires studying the structure and characteristics of discussions of vaccination in social networks. This study aims to analyze and describe the thematic structure of the discourse of vaccine hesitancy about vaccination against COVID-19 in the Russian-language segment of the Internet. Theoretically, the research bases on the concept of vaccine hesitancy and the social representations theory. The empirical data was collected in the Russian-language social network VKontakte. The authors carried out the thematic analysis of comments in four news communities of the selected social network and identified the main categories and topics of the online discourse of vaccine hesitancy. This discourse consists of four themes: the riskiness of vaccination, ineffectiveness of vaccination, unnecessary vaccination, and unfair vaccination. Based on this data, the authors identified the concepts and categories that make up the core and periphery of social representations of the vaccine hesitancy online discourse.