NEW YORK, N.Y. — Large-scale tests involving thousands of cattle have begun to determine whether animal vaccines can be a solution to help prevent E. coli O157H7 infections, according to an article in the New York Times.

After many years of delays in Washington, the tests are just starting. But even if they prove successful, the vaccines face an uncertain future because farmers and feedlot owners are concerned about who will pay for them in this low-margin business.

Regardless, scientists are optimistic such vaccines could significantly reduce the amount of E. coli O157:H7 bacteria cattle bring into slaughterhouses, which in turn would give existing hurdle technologies in-plant a greater possibility to kill remaining bacteria on carcasses and meat.

Many researchers believe E. coli vaccines can reduce the number of animals carrying the bacteria by 65% to 75%.

Two vaccines have been developed commercially, to date, to counter the E. coli threat. One is offered by Minnesota-based Epitopix; it received preliminary approval from U.S.D.A. in March, thus it can be sold while research continues. About 300,000 head of cattle will get the vaccine in the coming months as part of a series of large trials, according to Dr. James D. Sandstrom, general manager of Epitopix.

Bioniche Life Sciences, a Canadian company, has developed a second vaccine approved for use in Canada last year -- but it still awaits U.S. approval. Although Epitopix has yet to set a price for its vaccine, Bioniche charges about $3 a dose for its vaccine, which requires two or three doses per animal to be effective.