Here I give a brief description of the length of immunity expected from the pre 1980's smallpox vaccine (Dryvax) and the recommendations given by the CDC according to smallpox boosters.
Since both smallpox and monkeypox viruses fall under the same family of viruses (Orthopox) there is overlapping immunity generated within the family when one received the Dryvax vaccine. Depending on the area, many individuals born prior to the 1970-80's would have received the smallpox vaccine. This video is to highlight what their current level of protection may be several decades later.
Dryvax is no longer manufactured. It has been replaced by ACAM2000, following the same protocol. ACAM2000 is not administered to the general public, but rather stored in the Strategic National Stockpile for emergency use.
https://www.cdc.gov/smallpox/vaccine-...
https://www.cdc.gov/smallpox/clinicia...