Two reasons are working against vaccination as a solution: the lack of effectiveness and the likelihood that the United States would be banned from exporting poultry and poultry products after vaccination begins.
However, the U.S.D.A. continues to fund research to develop an effective vaccine.
The U.S.D.A. says 45 million birds have been lost to the H5N2 strain of avian influenza this year.
Minnesota has lost close to nine million birds from more than 100 outbreaks; Iowa has also been hard hit, including two egg farms with more than five million hens each and a third with about 3.8 million birds.
So far the vaccine has been tested on chickens in Minnesota; there have been no trials on turkeys.