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Health Team

One flu bug has learned to ignore antiviral drug

Posted March 10, 2009 5:47 p.m. EDT
Updated March 10, 2009 7:00 p.m. EDT

With the flu, symptoms generally are miserable and can become severe, and even life-threatening.

There are antiviral medications that may help lessen the symptoms and the duration of the bug if you take them within 48 hours of the first symptoms. But, one strain of the flu virus has become resistant to a commonly used antiviral drug.



Right now, we're in the peak of flu season, a time when the federal Centers for Disease Control and Prevention analyze influenza samples sent to its Atlanta headquarters from across the country.

There, doctors “use the information we obtain from them to tell us whether or not they're related to the influenza vaccine strain,” said Dr. Alicia Fry.

Researchers have noticed a distinct change in how one strain of the illness – called Influenza A (H1N1) – has become resistant to a common antiviral drug called oseltamivir.

“Last year, about 12 percent of the Influenza A H1N1 viruses were resistant to oseltamivir, and this season it looks like approximately 98 percent – almost 100 percent – of those viruses are resistant to oseltamivir,” Fry said.

The study, reported in the Journal of the American Medical Association, compared patients who had flu caused by an oseltamivir-resistant virus with those cases that were not resistant to the drug.

None of the patients took the antiviral medication before infection, so the resistance was not related to that.

“We found out that their illness was very similar to illness with an oseltamivir-susceptible virus, so there was no difference in infection,” Fry said.

In the end, when it comes to the flu, experts say prevention with a vaccination is key.

“Certainly, the current influenza vaccine is effective against this oseltamivir-resistant H1 strain,” Fry said.

That’s good news for those who have had a flu shot and a little motivation for those who haven't.