Abstract Background In an ongoing public health crisis, the question of why some people are unwilling to take vaccines with particular attributes is an especially pertinent one, since low rates of vaccination mean that it will take longer for many nations to exit the coronavirus disease 2019 (COVID-19) pandemic. Methods In this article, we conduct a pre-registered conjoint experiment in Hungary (N = 2512), where respondents were asked about their attitudes towards hypothetical COVID-19 vaccines whose characteristics varied across a number of attributes. Results Results indicate that vaccine attributes matter for the likelihood of uptake when it comes to the prevalence of severe side effects, efficacy and country of origin. Moreover, we find that our pre-treatment measure of institutional trust moderates the effect of our treatment, as differences in vaccine attributes are larger for those with robust levels of institutional trust compared to those with weaker levels. Conclusion Our findings suggest that institutional trust matters when it comes to understanding the relationship between vaccine attributes and likelihood of uptake.