The specific institutional design features used for building international alliances for producing and distributing COVID19 vaccines are likely to be crucial for citizens’ subsequent acceptance of, and cooperation with, vaccination policies. This study explores German citizens’ preferences for the building blocks of such international vaccine alliances. In a conjoint experiment, respondents are asked to compare two hypothetical vaccine alliances and to decide which of these Germany should join. The international alliance profiles vary with respect to four building blocks, each composed of two attributes: (1) alliance composition (size; Europeanness), (2) solidary distribution rules (allocation of costs; vaccine allocation), (3) vaccine nationalism (cost per German household; coverage in Germany), and (4) vaccine confidence (country of origin; producer type). We find that support for joining an international vaccine alliance depends on both attributes of vaccine nationalism and on vaccine origin, but not on solidary distribution rules or vaccine producer type. Further analyses demonstrate that support for an international vaccine alliance is strongly influenced by responds subjective perception of the threat they suffer from COVID19.