WASHINGTON — Federal officials are within a week of knowing whether a vaccine could prevent avian flu in turkeys, a welcome development for Minnesota’s devastated turkey industry.

Still, a vaccination wouldn’t be available until spring, too late halt any feared reoccurance of the lethal bird flu this fall. A vaccination also wouldn’t be a cure-all, and it could complicate trade relations with importers of U.S. poultry.

The U.S. Department of Agriculture already has developed a vaccine that has shown efficacy in chickens. David Swayne, director of the USDA’s Southeast Poultry Research Laboratory, said on Thursday a verdict was close on a turkey vaccination.

Swayne was speaking at a Congressional agricultural subcommittee hearing with some of the nation’s other top avian flu experts.

Rep. Collin Peterson, the highest-ranking Democrat on the House Agriculture Committee, told the subcommittee that Minnesota growers are still reeling from the biggest flu outbreak in U.S. history. “My state was ground zero for this,” he said.

The bird flu killed 9 million turkeys and egg-laying hens in Minnesota, wiping out about 10 percent of annual turkey production in the nation’s largest turkey-producing state. Only Iowa, the nation’s top egg state, was hit harder than Minnesota; about 31 million birds died there.

The last reported bird flu outbreak in Minnesota was June 5, and the turkey industry has been slowly rebuilding since. Forty-three turkey growers have signed “restocking” agreements with state regulators, while 31 have repopulated their barns with healthy birds, the Minnesota Board of Animal Health Board said Thursday.

The flu wiped out flocks at 108 Minnesota farms — most of them turkey operations — and has caused $650 million in economic losses, according University of Minnesota Extension. The hot summer weather has killed the virus for now, but experts say it may return with cooler weather this fall.

At Thursday’s hearing, Peterson urged USDA deputy administrator Dr. John Clifford to stockpile an effective vaccine, noting Minnesota producers are clamoring for it.

“In our part of the world, I’ve talked to the chicken people and the turkey people. … They would give up their [export] trade to get the vaccine,” Peterson said. Vaccinating birds usually disqualifies a country from foreign poultry trade because it’s an admission of flu presence.

But U.S. turkey exports are largely shut down now anyway, given the nation’s massive flu outbreak earlier this year. About 40 countries slapped restrictions on U.S. turkey imports.

The possible flu vaccine has been controversial within the poultry industry. While many turkey growers and egg-operators support it, the broiler industry — which has not been hit by the bird flu — has had reservations. Centered in the southern and southeastern United States, the broiler business does a big export trade.

The more demand for a vaccine, the more incentive drug companies would have to produce it — and vice-versa.

The turkey industry sees a vaccine as “another tool in the toolbox,” said Steve Olson, executive director of the Minnesota Turkey Growers Association. “We think it will create immunity in birds to help protect them.”

Still, growers must improve their biosecurity — their defenses against the spread of the flu.

“How we’ve handled this — we haven’t kept the virus out,” Olson said. However, Olson said growers are taking measures to better isolate their birds from outside contact and exposure.

The avian flu is believed to be transmitted by waterfowl who don’t get sick from the virus themselves, but shed it in their feces. Scientists believe the virus may have crept into poultry barns via workers, equipment, rodents and even the wind.

Olson said any vaccine wouldn’t likely be ready until spring. It would be administered to turkeys soon after birth.

At Thursday’s hearing of the Subcommittee on Livestock and Foreign Agriculture, there was also talk of how to better dispose of birds felled by the flu.

When the virus struck just one farm, tens of thousands of birds either died outright or were killed to stop the flu’s spread. Multiply that by dozens of farms in Minnesota and Iowa in a short time period, and delays added up. Birds sometimes sat dead for several days or even weeks before being cleaned up.

The problem was particularly acute with egg-laying chickens. Turkeys are killed on the spot in their barns with a suffocating foam. But chickens must be taken out of their cages and put into metal containers to be gassed by carbon dioxide, a much more labor intensive process.

Bill Hartmann, executive director of the Minnesota Board of Animal Health, told the subcommittee that officials are still exploring the best way to depopulate egg barns — sometimes stocked with more than 1 million hens — within 24 hours after an avian flu virus is detected.

Canadian officials have experimented filling the barns themselves with CO2. Hartmann said farmers also could shut off ventilation to the barn and let the birds suffocate in the heat, but he noted this method is not considered humane.

“But if you let the bird die over three weeks, I’m not sure that’s a very acceptable manner either,” Peterson said to him. “None of these options are very good. … We need to figure out a way to do this within 48 hours that doesn’t create a big furor in the public.”