CHICAGO (Reuters) - The U.S. Department of Agriculture on Tuesday said it has awarded contracts to two drug companies to manufacture doses of avian influenza vaccine for poultry, in preparation for the potential return of the fast-spreading avian influenza virus later this year.

The two contracted firms - Iowa-based Harrisvaccines, and France-based Ceva Corp. - will manufacture an undisclosed number of vaccine doses and store those doses for up to 5 years, USDA said in a statement released late Tuesday.

In addition, the companies are required to test the vaccines regularly for potency, as well as deliver finished vaccines anywhere in the United States within 10 days of a request for them from the National Veterinary Stockpile.

Separately, the agency and Iowa State University have translated USDA biosecurity training materials from English into Spanish, in an effort to help farmers and on-farm workers better understand ways to prevent bird flu infections ahead of the potential resurgence. Iowa is the country's top egg producing state and was the epicenter of the worst ever U.S. bird flu outbreak, which forced the culling of almost 50 million birds nationwide.

The agency's Animal and Plant Health Inspection Service (APHIS) has not approved the use of an avian influenza vaccine in birds, and has not made a decision whether to use such vaccines in a future outbreak, USDA said Tuesday.

But in August, the agency said it wanted to create a stockpile of vaccine for the Eurasian H5 strain seen in the outbreak in the United States earlier this year. At the time, APHIS issued request for proposals (RFPs) from vaccine manufacturers.

USDA said APHIS will continue to issue such RFPs quarterly from now through September 2016, in an effort to have vaccine makers develop and produce other products that can help bolster the vaccine stockpile if another avian influenza outbreak happens in the U.S.

(Reporting by P.J. Huffstutter; Editing by Andrew Hay)