My brain understanding was there is 4, can you list the other 2?
https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines/overview-COVID-19-vaccines.html
Pfizer/bioNTech
Moderna
AstraZeneca/Oxford
J&J/Janssen
Novavax
Sanofi/GSK
They weren’t all used in the US but they were part of the program.
Merck was also working on one but abandoned it.
https://crsreports.congress.gov/product/pdf/IN/IN11560