Iowa State University's Hank Harris, professor of animal science, developed the vaccine this summer and has been shipping preventive doses to swine producers in Iowa, Kansas and Illinois for several weeks.

The latest vaccines were shipped to a swine producer in Indiana that had H1N1 diagnosed in the herd. "This is the first time we've had a confirmed diagnosis and the farmer wanted to vaccinate," said Harris. "We shipped about 20,000 with about another 11,000 doses to go out to them later."

Vaccinating a herd that has already been infected should have some effect on the spread, but Harris isn't sure how much. Harris' vaccinations have recently been reviewed and published by the online journal PLoS Current Influenza.

"It isn't uncommon for vaccinations to be used in what we call 'the face of an outbreak,'" he said. "They (producers) may think the virus is spreading slowly in the herd, and they want to vaccinate the entire herd."

Harris thinks the Indiana vaccinations may indicate swine producers around the country are eager to vaccinate. "Since these pigs got sick and had a confirmed diagnosis, I think more farmers are going to want to vaccinate," he said.

Harris says that the virus may have gotten into the Indiana swine herd from humans who had flu-like symptoms while working with the pigs. "It's one of those things we'll probably never know for sure. The history is that the virus can go from people to pigs and from pigs to people just as easily," he said.

The vaccine is being manufactured through Iowa State University and Harris' startup company Harrisvaccines, Inc. d/b/a SirrahBios, Inc.