LINCOLN, Neb. — Humans might not be the only ones guarding against swine flu by the time cold weather ushers in influenza season. The flu namesakes also could be getting new vaccinations.

The U.S. Department of Agriculture gave several animal vaccine manufacturers the "master seed virus" from the swine flu strain now circulating among humans. At least one of the companies said Wednesday it's developing a vaccination for pigs, which can contract the virus from infected people — in much the same way people do.

Flu viruses pass from human to hog mostly from coughing and sneezing, according to the Centers for Disease Control and Prevention.

A pig vaccine would help livestock producers prevent their animals from getting the novel H1N1 strain commonly called swine flu, as well as help thwart the development of other flu strains that could endanger humans and animals in the future.

Pigs, which also are susceptible to avian and human flu strains, are considered mixing vessels where the viruses can mutate.

"Through that mutation they can become more virulent and could cause problems in humans," said Dr. John Clifford, chief veterinarian for the USDA's animal-health division. "Also, for pigs themselves, if the virus changes, current vaccinations may not work."

So far, the swine flu causing global health concerns has not turned up in U.S. pig herds. But it has been found in herds in Canada, Argentina and Australia. Canadian officials announced the first documented case of the human H1N1 virus jumping from a person to pigs on a farm in May.