How the flu kills

Influenza can take opposite routes to overcome people’s immune systems

Health officials say the recent outbreaks of H1N1 – or swine flu – have had pretty mild effects. Even during the regular flu season 99.9 percent of patients survive infection. Researchers at the Children’s Hospital of Philadelphia are trying to figure out why that point one percent die from the illness.

Listen: [audio:090508kgflu.mp3]

Kate Sullivan and her colleagues examined the immune systems of children who became exceptionally sick with regular, seasonal flu. And for some of the kids, they found that the flu sent their immune systems into overdrive and caused inflammation. They expected that finding, because that’s how flu pandemics have killed people in the past. But then there was something surprising.

Sullivan: It turns out that the flu virus can actually suppress the immune system.

So…some of the kids, the flu was having the opposite effect — shutting down their immune systems.

Sullivan: In a way that specifically allows the person to be susceptible to bacterial pneumonia.

And these children ended up dying…from pneumonia. Sullivan says they still don’t know why the virus can have opposite effects in people. And it’s too early to tell which route this new swine flu tends to take.