Re people who had smallpox vaxes in the distant past: estimates are that immunity would have dropped to as low as 5% of peak by now. Medical workers fighting SP epidemics back when, were getting revaccinated at least weekly (some DAILY). Anyway, except for some medical workers, virtually no one in the West under 45 has had the SP vax at all.
Oh, and several commie countries had big research programs going as recently as the late 1990s on strains immune to the current vaccines. The Norks had up to railroad tanker size fermenters full of concentrated media of these. One of the more effective versions was named the "India" strain.
Three more: 1) the Soviet Army stopped vaccinating their troops vs. SP for about 5 years in the early 80s, after SP was officially wiped out, but then started back up. 2) One of the last ICBM tests done before the USSR imploded in 1991 was a flight that traveled the length of the country (11 time zones), so plenty of range to hit most anywhere worth targeting. It had odd flight characteristics, that eventually were deemed by the spooks to be consistent with a refrigerated payload. 3) IIRC, some yahoo a few years ago posted the exact genetic design of the Variola Major virus (the one that causes smallpox) on the Internet. There are facilities that now have the capability to synthesize entire viruses from lab chemicals with nothing more than that to start with.
Smallpox no longer a threat? My @ss it's not.