DES MOINES - Low-cost vaccines that may help prevent the kind of salmonella outbreak that has led to the recall of more than a half-billion eggs haven't been given to nearly half the nation's egg-laying hens.
The vaccines aren't required in the United States.
In Great Britain, officials say vaccinations have given them the safest egg supply in Europe.
A survey conducted by the European food safety agency in 2009 found about 1 percent of British flocks had salmonella, compared with about 60 to 70 percent of flocks elsewhere in Europe, said Amanda Cryer, spokesman for the British Egg Information Service.
Since Britain's vaccinations began, the only salmonella outbreaks in eggs have been linked to imports from elsewhere in the European Union, she said.
There's been no push to require vaccination in the United States, in part because it would cost farmers and in part because advocates have been more focused on more comprehensive food safety reforms, those watching the poultry industry said.
The U.S. Food and Drug Administration has not determined how the hens in Iowa became infected.
About 125 million of the 218 million egg-laying hens in the United States have been vaccinated, said Gary Baxter, a spokesman for French pharmaceutical company CEVA, which sells some of the vaccines in the United States.
The salmonella vaccine prevents hens from becoming infected and then passing the bacteria on in their eggs. It has been available in the United States since 1992.