Some strains are resistant to antibiotics or can be made resistant, while the cumbersome vaccine involves six shots and an annual booster.

They offer significant degrees of protection for up to two years after a single shot, and for three to four years with annual booster.

He said he had previously had a limited number of anthrax vaccinations, including an annual booster to maintain immunity.

After that an annual booster maintains contraception.

Dogs receive a sequence of two doses, then an annual booster.

The first vaccinations - a series of six shots over 18 months, followed by annual boosters - began the next year.

The NYT lead reports that the Pentagon anthrax inoculation program will consist of a series of six shots to start with and then annual boosters.

The present anthrax vaccine is not ideal - it requires six separate injections with an annual booster - and is in any case reserved for military use.

Beyond that, there may be a need for an annual booster, depending on studies taking place of vaccinated people.

Individuals can be protected by a vaccine given in a series of six doses followed by annual boosters, a cumbersome regimen.