Looks like all the anti-terrorism protection is unnecessary as the largest research project of its kind ever conducted shows 90 percent of those vaccinated with smallpox maintain a substantial level of immunity, even if the immunization was up to 75 years ago.
Researchers also concluded that in the long term, repeated vaccinations do not result in a higher level of disease protection.
It is all a moot issue anyway, as it is likely the vaccines are not necessary to avoid smallpox. If this sounds like heresy then you have likely not read why hygiene is more important than vaccination against smallpox.
Nature Medicine September 2003