The anthrax letters did not test anyone's vaccine. For people exposed to the anthrax letters, anthrax vaccine was given in three doses over 4 weeks. It takes about 4-6 weeks after vaccinations start before recipients develop levels of antibodies to anthrax that may be protective.
The vaccine's label even points out that anthrax vaccine is NOT a treatment for anthrax and does not provide protection for acute exposures. You need to take antibiotics while waiting for vaccine protection to develop...and because vaccine protection is variable, and depends on each person's ability to mount a protective immune response, antibiotics are a much more reliable protection, even after 2-3 doses of vaccine have been administered and 4-6 weeks have gone by.
So no scientist would send anthrax letters to "test a vaccine." It's a ridiculous theory.
Did the person who fed this idea to the media (in a desperate attempt to create a motive that could implicate Bruce Ivins) have anything to do with the anthrax letters? Or perhaps work for the Justice Department?