I was vaccinated. Back then, it was meant to last a lifetime. Not sure that's the case, though.
Its one of the oldest vaccines. We started giving it in the 1800s and it was eradicated in the 70's. If immunity waned, it would have been noticed back when smallpox was still a thing by people getting smallpox.
The military was still vaccinating in '81, when I joined.
Still vaccinating in select areas. In 2007 deployed to the Republic of Korea and was vaccinated.