This risk has been acknowledged for a long time. Shortly after 9/11 and the anthrax attacks in 2001, the US began stockpiling enough smallpox vaccine for the whole country[1].

They claim to have kept that stockpile going[2] but they also said the same of the PPE stockpile...

[1] - https://www.cidrap.umn.edu/news-perspective/2001/11/acambis-...

[2] - https://www.cdc.gov/smallpox/bioterrorism-response-planning/...