Vaccines can be an appropriate tool for combating pandemics. Accordingly, expectations were high when the first Covid-19 vaccines were administered. However, even though the vaccines have not met these high initial expectations, vaccine manufacturers and their investors were making large profits, while most of the associated economic risks have remained with the taxpaying public. Thus, this paper applies the concept of social impact bonds to mass vaccination programs by conceptualizing vaccine impact bonds (VIBs) as an alternative to the advance purchase (...) agreements (APAs) for Covid-19 vaccines. Rather than rewarding vaccine manufacturers and their investors based on the quantity of doses distributed, VIBs intend to link the real-world vaccine impact to the financial returns of vaccine manufacturers and their investors. This paper indicates that VIBs can theoretically shift the economic risks of mass vaccination programs from the taxpaying public to private investors, thereby aligning commercial and public interests. However, it also identifies several major weaknesses such as the complexity of defining and evaluating the vaccine impact as well as the inherent trade-off between relieving taxpayers (through VIBs) and allowing innovation. As these substantial drawbacks outweigh the theoretical strengths of VIBs, this paper calls for further research in order to identify better alternatives to the Covid-19 vaccine contracts. (shrink)