It works within a window. Variola goes "dormant" for a few weeks before breaking out into smallpox. If you can get an immediate response to vaccinia before the rash begins, the vaccine is very therapuetic. I'll have to track down the numbers, but in almost every case of exposure it has been beneficial to vaccinate most do not come down with the dz, and those that do have very mild symptoms, relatively speaking.
it takes 2 weeks after a vaccine for the antibody response to begin.
You begin to get an IgM response immediately, but it usually takes 2-3 days to get large measureable numbers, this is closely followed by an antibody switch to IgG (the antibody type most closes associated with immunological "memory"). After 5 days for most healthy adults you'll have the response necessary to fight variola if given the vaccine
That may work if you know immediately that you were exposed to someone with smallpox and could try to get your immunity up before the virus has spread through your body (or your kids'), but if you only realize it when you start seeing the blisters, it would be too late. I think I'll stay with the idea of getting my kids out of the country for a while and into some remote area where there aren't many people. I can do that unless they block us from leaving.
One of the real problems with this whole discussion is who do you believe? Since Sept. 11 when the questions about the possibility of a small pox bio-attack have been raised, I've seen only two sides, either "we're all gonna die" or, "it won't be a problem, go back to your lives citizens". Where does one go for realistic information that will allow us to be prepared without freaking out needlessly?