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Objective: In 2021, thrombocytopenia syndrome (TTS) was confirmed by the European Medicines Agency (EMA) as a rare side effect of the COVID-19 adenovirus vector vaccines from AstraZeneca or Janssen. This study aimed to describe the public’s knowledge of TTS and how it affected the willingness to be vaccinated with COVID-19 and other vaccines.Methods: In 2022, a multi-country cross-sectional online survey was conducted in Denmark, Greece, Latvia, Netherlands, Portugal and Slovenia. The minimum target of participants to be recruited was linked to the country’s population. The results were analysed descriptively. Results: In total, 3794 respondents were included in the analysis. Many (33.3% to 68.3%) reported being aware about TTS and its association with the vaccines from AstraZeneca and Janssen, though most were not familiar with the exact symptoms. Changes in willingness to be vaccinated with COVID-19 and other vaccines varied by country. The largest change in the willingness to be vaccinated with AstraZeneca and Janssen vaccines was in Denmark (61.2%), while the largest change in the willingness to be vaccinated with other COVID-19 vaccines was in Slovenia (30.4%).Conclusion: Information about TTS seemed to be considered by the public in the European countries resulting in changed willingness to be vaccinated with the COVID-19 vaccines from AstraZeneca and Janssen. Willingness to be vaccinated against other COVID-19 vaccines and vaccines in general seemed to be determined by the approaches of the national health authorities to react to and communicate about the COVID-19 vaccination risks. Further investigation of risk communication strategies is warranted.