there was not enough evidence to conclude that vaccinating hens against salmonella would prevent people from getting sick. The Food and Drug Administration decided not to mandate vaccination of hens — a precaution that would cost less than a penny per a dozen eggs.
many industry experts say the absence of mandatory vaccination greatly weakens the F.D.A. rules, depriving them of a crucial step that could prevent future outbreaks.
One-half to two-thirds of American farmers already inoculate their flocks, according to industry estimates, and that number is likely to increase. While the new federal rules do not require vaccination, they do require testing for salmonella.
Click on the following for more details: U.S. Forgoes Salmonella Vaccine for Egg Safety - NYTimes.com