1) Schoolchildren innoculations basically stopped in 1972, a combination of smallpox being eradicated and the accidental death rate (some fraction innoculated die).
No smallpox vaccine is currently commercially available today. You can't buy the stuff. There are small stockpiles of the vaccine in case this "extinct" virus comes back someday, but it's hard to imagine that they could be administered in time to do any good. If it were possible to buy the stuff, I would get vaccinated right now, but someone doesn't want us to be able to get it. You might say that it's because of liability laws, but this isn't true, because you can't buy it in any country, even countries without liability laws or functioning civil court systems. The lie they say for denying the vaccine is that because the virus is extinct, there is no risk of infection, and there is a risk of dying from the vaccine, so it is too unsafe to use. This is disgusting because everyone knows that it is a lie; the virus is nowhere near extinct, and probably exists in dozens of labs around the world, and there is a very real danger of becoming infected with smallpox, but because no one has used it as a bioweapon in this century, the probability of it cannot be measured, but it is almost certain that the risk of being infected is currently higher than the risk of dying from the vaccine.
2) Innoculations/vaccinations are _not_ lifetime...they tend to wear off in about 30 years. (The 1972-2001 time period is just a coincidence.)
However, someone who was vaccinated, even decades ago, probably has some more residual resistance than those who never recieved it. Maybe.
4) However, it was _not_ extinct. The U.S. kept cultures of it, and the Soviets had an extensive program to develop "militarized smallpox": more virulent and better-suited for distribution from artillery shells.
It is most definitely not extinct. One of the stupidist most hypocritical scientific things I have ever seen was some stupid ceremony where the "last vials of smallpox" held in both the US and Russia were simultaneously destroyed a few years ago. Not one single thoughtful person could possibly believe that that was the last trace of smallpox, and yet they had a bunch of scientists saying how wonderful it was. They knew with absolute certainty that this wasn't true, because how on earth could you believe that the CIA/KGB/Mossad/ISI/etc haven't all kept little samples? Anyway, even if every lab destroyed its samples, it still doesn't make it extinct. It is almost certain that some virus would survive in old grave sites, etc. As I said, there are vaccines in a stockpile, but not remotely enough for the entire US population, and they are not available anyway. Someone made the conscious decision that the US population should be made vulnerable to this virus. One interesting point is that you could make your own vaccine in various ways. One is to infect yourself with cowpox, a related disease which is not harmful to humans, but which confers immunity. The other is to prepare the vaccine by taking samples from an infected person and inactivating them in various ways. Smallpox was the first vaccine to be developed, and it was done long before modern biology existed, so it's the easiest one to make.