Background: Several research studies have examined the reasons why people are hesitant to be vaccinated against COVID-19. However, there is no published data to date on Switzerland. Identifying these reasons among the Swiss population who are vaccine hesitant may help inform campaigns to encourage vaccine confidence.Aims: The primary aim of this study is to identify the reasons for not getting vaccinated against COVID-19 among Swiss residents who are vaccine hesitant. The secondary aim is to examine whether reasons differ by age, gender, education, and likelihood of accepting a vaccination to better target campaigns and design interventions.Design: An online survey asked participants to indicate the reasons why they were hesitant to be vaccinated against COVID-19. Setting: German-speaking Swiss Cantons, the survey was administered online between 5 May 2021 and 16 May 2021.Participants: The participants in this analysis were a sample of (N=1191) Swiss residents age 16-60 years old from German-speaking Cantons, who could answer an online survey in German, who had yet not been vaccinated, who had not yet registered for a vaccination appointment, and who did not indicate that they would definitely be vaccinated if offered the chance.Findings: Among people who are vaccine hesitant in Switzerland, the most common reasons for being hesitant were side-effect, safety, and effectiveness concerns. It was also common for people to indicate that they were healthy/at low risk, would decide later, and that they wanted to build immunity naturally. Less common, but still prevalent concerns included wanting more information, thinking COVID-19 was not a real threat, and concerns that the vaccine may serve another purpose. Differences in reasons for being vaccine hesitant were found by age, gender, education, and likelihood of accepting a vaccination if offered.Conclusions: To increase the likelihood of accepting a vaccination, vaccination campaigns should address side-effect, safety, and effectiveness concerns. Campaigns could also consider informing people why it is necessary for people in lower risk groups to be vaccinated, and why vaccination is preferable to infection for building immunity. While campaigns may be effective in reaching some of the population, alternative strategies might be necessary to strengthen the trust relationship with vaccines and vaccine providers in some groups. Less prevalent concerns, such as not liking needles, could be addressed through individual level interventions.