HARTFORD, Conn. (AP) - The state will take the unprecedented step of vaccinating millions of chickens in response to an outbreak of avian influenza at Connecticut's largest egg farm.

The only other alternative would be destroying the 3 million infected birds at Kofkoff Egg Farm, acting Agriculture Commissioner Bruce Gresczyk said Friday. That would be a severe blow to the regional economy and the farm, which has operations in five eastern Connecticut towns.

"The spinoff effect of jobs and businesses would be in jeopardy," Gresczyk said.

The vaccinations require federal approval because the serum is at a state laboratory in Maine and must be transported across state lines. U.S. Department of Agriculture approval is expected within the next two weeks. The vaccinations are part of an eradication pilot program.

"It's never been done on such a large scale before," Gresczyk said.

A mild form of the disease was suspected two weeks ago and was confirmed this week in the Kofkoff chickens. The infected birds were at the farm's Mack Road coops Lebanon and on Schwartz Road in Bozrah.

"It went through the entire complex," Gresczyk said.

The outbreak prompted Japan to temporarily ban all U.S. poultry imports. Japan lifted the ban after receiving assurance that proper steps were being taken; however, a ban on Connecticut poultry remains in effect.

The illness resulted in just a few bird deaths, Gresczyk said. Those that recovered have a lifetime immunity, Gresczyk said.

"It passed through them like the common cold and they will never get it again," he said.

The low-pathogen form of the disease does not affect humans or other mammals. It also does not the affect eggs, and egg production has resumed at a normal level, he said.

About 1.25 million birds at Kofkoff's other coops on smaller sites in Lebanon, Bozrah and Franklin were not infected, he said.

Agriculture officials are awaiting test results next week on Kofkoff birds at coops in Hebron and Colchester, but expect them to be negative because those birds showed no signs of the disease.

Strict quarantine and biosecurity measures remain at Kofkoff and the state has broadened its surveillance to farms with 500 or more birds. State agriculture officials say they are in constant contact with USDA veterinarians and agriculture officials in other Northeast states where the investigation is widening.

"We'll know better in a few weeks if we have it anywhere else in Connecticut and in a few months if we have it anywhere in New England," Gresczyk said.

Kofkoff supplies nearly 90 percent of the eggs in the state and much of the New England market, producing nearly 24 million eggs a week. It employs 290 people and has an annual payroll of $11 million. The farm also is the largest customer of the New England Central Railroad. Nearly 40 percent of the railroad's cargo is chicken feed, Gresczyk said.

"Depopulation just wasn't a workable option," Gresczyk said.

Destroying the chickens also would have cost the state about $35 million.

Instead, the state will supervise the vaccination of pullets, or young replacement chickens, as they enter the production line. Laying hens generally have a life span of 2 years on the line, Gresczyk said.

The farm will bear the cost of the vaccines. Gresczyk had no estimate of the vaccine price. Repeated calls seeking comment to Kofkoff managers were not returned.

The source of the disease has not been determined but there are possibilities, including infected wild fowl. Gresczyk said the state Department of Environmental Protection plans to test wild turkeys.

"This is something we always dreaded," Gresczyk said. "Fortunately, we planned for it."