Low-cost vaccines that may have helped prevent the kind of salmonella outbreak that has led to the recall of more than a half-billion eggs haven't been given to half of the nation's egg-laying hens.
The vaccines aren't required in the U.S., although 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 that about 1 percent of British flocks had salmonella compared to about 60 to 70 percent of flocks elsewhere in Europe, said Amanda Cryer, spokeswoman for the British Egg Information Service.
There's been no push to require vaccination in the U.S., 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.
But Darrell Trampel, a poultry veterinarian at Iowa State University, predicted vaccination will become more common after the recent outbreak.
"I think (vaccination) will move from hit and miss to being a standard," Trampel said.
The salmonella vaccine prevents chickens from becoming infected and then passing the bacteria on to their eggs. It has been available in the U.S. since 1992.
There are two forms. One is a spray that uses a live bacteria, and chickens inhale it. The other contains dead bacteria that's injected. Jewanna Porter, a spokeswoman for the Egg Safety Center, an industry group, said both forms provide good protection. The injected vaccine lasts longer, but veterinarians recommend both be updated.
In most cases, laying hens are vaccinated at between 10 and 16 weeks old, which is before they are put into production.
The U.S. Food and Drug Administration said last month it doesn't believe mandatory vaccination is necessary, but it supports farmers doing it voluntarily.
Data on the vaccine's effectiveness in field trials conducted in real world conditions "was insufficient to support a mandatory vaccination requirement," the agency said in the text of new rules requiring increased inspections and testing of eggs.
"If individual producers have identified vaccines that are effective for particular farms, FDA encourages the use of vaccine as an additional preventative measure," the agency said.
Telephone and e-mail messages left for FDA spokeswoman Patricia El-Hinnawy for further explanation were not immediately returned Tuesday.
Doug Grian-Sherman, senior scientist at the Union of Concerned Scientists, said the vaccine deserves additional study, but it would likely have only have limited effectiveness against a bacteria like salmonella, which has many different strains.
"It's only going to be a Band-Aid on a much bigger problem," he said.
It would be more effective to give the FDA additional authority to stop repeat offenders and pull contaminated products off shelves and to move away from big production facilities that ship across the nation and can quickly spread disease, Grian-Sherman said.
"The way we produce a lot of our food and meat and eggs in particular, has gotten to a scale where it's very difficult to prevent these problems," he said. "That needs to change and we need to think about producing food on a scale that is better for the communities and safer for consumers."
Trample, the Iowa State University veterinarian, said no vaccine for any disease is required for chickens.
"They are all left up to the decision of the producer," he said. "Almost all other vaccines are strictly for chicken diseases that have no public health significance."
The FDA has not yet determined how the hens in Iowa became infected, said Dr. Jeff Farrar, FDA's associate commissioner for food protection.
Both farms involved in the recall vaccinated some of their chickens.
Julie DeYoung, a spokeswoman for Hillandale Farms, said the company began purchasing vaccinated laying hens in September 2009. The company didn't vaccinate older hens but replaced them with vaccinated ones as they went out of production, she said.
"So about 80 percent of the hens have been vaccinated," DeYoung said.
Wright County Egg has vaccinated some hens since 2009, investing more than $570,000 in the effort, spokeswoman Hinda Mitchell said. She declined to offer details due to an FDA investigation but said young hens were vaccinated "when they are in our care."
El-Hinnawy said it appeared the company vaccinated some but not all of its hens.
In Great Britain, farmers use a vaccine that goes into the water hens drink. The British government began encouraging, but not requiring, vaccination after a salmonella scare in the late 1980s crippled its egg industry. There was a 60 percent drop in egg sales overnight, Cryer said.
"Looking back, that scare was probably the best thing for the industry because we sorted out the problem, and we now have very high standards and there are no consumer concerns about safety," she said.
At least 90 percent of eggs in Great Britain come from vaccinated hens. The other 10 percent come from very small farmers who may have vaccinated chickens but don't sell to major retailers.
Since vaccinations began in Britain, the only salmonella outbreaks in eggs have been linked to those imported from elsewhere in the European Union, namely Spain, Cryer said.
Dr. George Boggan, a veterinarian with the French pharmaceutical company CEVA, which makes some of the vaccines available in the U.S., said they aren't always effective. If egg farms are dirty, and there's a lot of contamination, the bacteria can "overwhelm" the protection from the vaccine, he said.
"It's in the best interest to keep the environment as clean as possible," Boggan said.
S&R Farms near Whitewater, Wis., began inoculating its 2.5 million hens seven years ago.
"We kept our birds on that program and we've never had a positive (salmonella) result in the thousands of tests we've done," manager Dave Hill said.
He didn't know exactly how much the company paid for the vaccines, but others estimated vaccination costs between 40 and 60 cents per bird. That includes the cost of the vaccine and the expense involved in administering it.
"It's a relatively inexpensive thing to do for the safety you get from it," Hill said.
AP Medical Writer Maria Cheng in London contributed to this report.