Doubts about vaccination in spite of the availability of vaccines are called “vaccine hesitancy”. In the digital age vaccine hesitancy is significantly influenced by information from the Internet, online communication and discussions on social media. The research of the language of such discussion is very important for understanding attitudes of people towards vaccination. The vaccine hesitancy discourse varies from country to country due to its social context, but also has many similarities. The aim of the research was to describe the thematic structure of the online discourse of vaccine hesitancy in social media. We analyzed Russian language social media discussions around COVID-19 vaccination. Comments were selected from four most active discussion groups. Thematic analysis was implemented for data organization and interpretation. Main themes identified are as follows: doubts about the safety of vaccination; doubts about the effectiveness of vaccination; doubts about the need for vaccination; doubts about the fairness of vaccination. The study of discourses of vaccine hesitancy in different languages makes a significant contribution to understanding the general patterns of functioning of discourse in the field of health, in particular, discourse about vaccination.