If we are talking about the US, then the taxpayers are liable.
In the specific case of the COVID-19 vaccines, they are explicitly NOT covered by VICP, but rather the CICP.
[Countermeasures Injury Compensation Program (CICP) | Official web site of the U.S. Health Resources & Services Administration](https://www.hrsa.gov/cicp)
The Wikipedia page does not clarify either: https://en.wikipedia.org/wiki/National_Vaccine_Injury_Compen...