Salmonella outbreak turns focus to vaccine

But when US regulators created egg safety rules that went into effect last month, they declared 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 dozen eggs.

Now, consumers have been shaken by one of the largest egg recalls ever, involving nearly 550 million eggs from two Iowa producers, after a nationwide outbreak of thousands of cases of salmonella was traced to eggs contaminated with the bacteria.

The FDA has said that if its egg safety rules had gone into effect earlier, the crisis might have been averted. Those rules include regular testing for contamination, cleanliness standards for henhouses, and refrigeration requirements, all of which specialists say are necessary.

However, many industry experts say the absence of mandatory vaccination greatly weakens the FDA rules, depriving them of a crucial step that could prevent future outbreaks.

Salmonella bacteria are passed from infected hens to the interior of eggs when they are being formed. The salmonella vaccines work both by reducing the number of hens that get infected and by making it more difficult for salmonella bacteria to pass through to the eggs.

“They are the only thing I’m aware of that really controls the problem from the inside out, at the source,’’ said Ronald Plylar, former president of a company that developed an early salmonella vaccine.

Many people in the US egg industry say they believe that the current outbreak and recall will tip the balance and force nearly all producers in the United States to begin vaccinating hens to reassure consumers.

The FDA said it considered mandatory vaccination seriously. “We didn’t believe that, based on the data we had, there was sufficient scientific evidence for us to require it,’’ said Dr. Nega Beru, director of the agency’s Office of Food Safety.

However, Beru says, the new rules encourage producers to vaccinate if they think it will help fight salmonella.

Another FDA food safety official, Nancy S. Bufano, said that despite the success of vaccination in Britain, the agency thought that because the vaccines used in the two countries were not identical, it made comparisons difficult.

Vaccine company executives, however, said the differences were minor and the drugs used in both countries were equally effective.

The FDA has estimated that it would cost farmers about 14 cents a bird to vaccinate, or about $31 million to cover hens at all the large farms in the country. But vaccine company executives said the cost can be just a few cents a bird, depending on the type of vaccine.

After the current outbreak, “many producers that were trying to decide whether or not to vaccinate will now vaccinate,’’ said David Zacek, the chief executive of Lohmann Animal Health International, one of three companies that produce the vaccines in the United States.