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.
While human spread doesn't yet seem to be happening, the CDC is on high alert. It's not yet flu season, but it is state fair season.
Shaw warns that people who come into contact with pigs -- particularly children -- may be susceptible to the new bug. People especially susceptible to flu -- including very young kids, pregnant women, the elderly, and people with suppressed immune systems -- should avoid contact with swine.
Why? If pigs in Pennsylvania and Indiana are infected, it's likely that pigs across North America are carrying the new flu bug.
"It is almost like the entire swine population in North America is one big herd," Shaw says. "That is because of movement the animals at many stages of production from breeding to slaughter."
People cannot get any kind of swine flu bug from eating pork.