Abstract
BACKGROUND: The aim of this study was to evaluate beliefs about and attitudes towards COVID-19 booster vaccination among subjects who had received the complete vaccination schedule but had not received the booster. METHODS: We conducted a qualitative study using online focus groups made up of participants from all parts of Spain who had received the primary vaccination schedule but had subsequently refused any of the booster doses. Individuals were recruited by snowball sampling. RESULTS: The study used 5 focus groups having a total of 30 participants. The thematic analysis identified 10 themes and 32 subthemes. Gynaecological problems and long-term adverse effects were associated with booster hesitancy. Participants perceived the vaccine as less necessary, as they considered it incapable of halting transmission and believed that the risk was much lower than at the onset of the pandemic. Rapid development of the COVID vaccine as compared to that of traditional vaccines, coupled with continuous changes in information, generated distrust and contributed to booster vaccine hesitancy. CONCLUSIONS: Vaccine hesitancy can appear at any time and with any vaccine despite its evident public health benefits, as is the case of COVID-19 booster doses. Policy-makers should therefore focus on generating trust and responsibility when it comes to booster vaccinations. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12889-026-26674-0.