During the COVID-19 pandemic, many residents of high-income countries (HICs) were eligible for COVID-19 vaccine boosters, while many residents of lower-income countries (LICs) had not yet received a first dose. HICs made some efforts to contribute to COVID-19 vaccination efforts in LICs, but these efforts were limited in scale. A new literature discusses the normative importance of an international redistribution of vaccines. Our analysis contributes an empirical perspective on the willingness of citizens in a HIC to contribute to such efforts (which we term international vaccine solidarity). We analyse the levels and predictors of international vaccine solidarity. We surveyed a representative sample of German adults (n = 2019) who participated in a two-wave YouGov online survey (w1: Sep 13–21, 2021 and w2: Oct 4–13, 2021). International vaccine solidarity is measured by asking respondents preferences for sharing vaccine supplies internationally versus using that supply as boosters for the domestic population. We examine a set of pre-registered hypotheses. Almost half of the respondents in our sample (48%) prioritize giving doses to citizens in less developed countries. A third of respondents (33%) prefer to use available doses as boosters domestically, and a fifth of respondents (19%) did not report a preference. In line with our hypotheses, respondents higher in cosmopolitanism and empathy, and those who support domestic redistribution exhibit more support for international dose-sharing. Older respondents (who might be more at risk) do not consistently show less support for vaccine solidarity. These results help us to get a better understanding of the way citizens’ form preferences about a mechanism that redistributes medical supplies internationally during a global crisis.