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New Swine Flu in 2 U.S. Kids

New Bug Has Gene From Pandemic Swine Flu; No Sign Yet of Human Spread
WebMD Health News
Reviewed by Laura J. Martin, MD

Sept. 2, 2011 -- Two U.S. kids -- an Indiana boy and a Pennsylvania girl -- are the first human cases of a new swine flu bug.

Both kids fully recovered after suffering usual flu symptoms.

The two children had no contact with each other. Each caught the new flu in separate transmission events. The boy's case was reported on Aug. 17; the girl's on Aug. 24.

"We have been able to detect a novel flu virus," CDC spokesman Tom Skinner tells WebMD. "It is an H3N2 swine flu virus that has picked up a gene from 2009 H1N1. We are investigating whether human-to-human spread is occurring."

Human-to-human spread appears possible, as the boy seems to have been infected by a caretaker who had contact with pigs. But so far there's no evidence of sustained person-to-person spread. A preliminary investigation in Indiana found no spread of the virus beyond the infected boy.

This is far from the first time humans may have caught swine flu viruses directly from pigs. The CDC knows of 21 cases from December 2005 to December 2010.

But it's the first time the 2009 swine flu virus currently circulating in humans has recombined with an older swine flu bug. The new flu is a reassortment in which the old swine H3N2 virus incorporates a single structural gene from the 2009 H1N1 virus, says CDC virologist Mike Shaw, PhD.

This 2009 H1N1 gene is unlikely to make the bug cause more severe disease or to make it more easy to catch, he tells WebMD.

Preventing Swine Flu

Pigs actually got the H3N2 virus from humans. It's the flu bug that caused human disease in the 1990s.

Because the "H" and "N" components of flu bugs stimulate immune responses, many adults may already have at least partial immunity to the new H3N2 swine flu.

Not so for children. Both of the kids who came down with the new bug were under 5 years of age.

Both kids got their flu shots last September -- but it did not protect them against the new swine flu. The CDC confirms that the current flu shot is not expected to protect against the new virus.

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