With the increasing threat of biological terrorism, it's tempting to vaccinate everybody for all known diseases. But even if we had enough to go around, it would be enormously expensive. Vaccines also carry risks that would be unacceptable just because a terrorist might strike. For example, suppose a vaccine for anthrax has serious side effects (death or permanent disability) at a rate of one in a million (that's pretty low), then vaccinating everybody in the US would lead to 300 or so cases. That's much bigger than the number of people killed in this latest round of anthrax.
So what should we do in the face of biological terror? Oliver Morton's article in Wired magazine presents this idea:
Another distributed response to biological attack is partial immunity. There are already vaccines against most plausible bioweapon agents. If a small percentage of health workers – and indeed of the population at large – were to choose to be vaccinated against one or some of these diseases, then a reservoir of manpower would always be on hand in an emergency, ready to help with the vaccination of others or to do whatever else was necessary in places where infection was rife. You can't vaccinate everyone against everything; but if some people are vaccinated against most things and you know where to find them, their distributed immunity could be a powerful asset.