December 20, 2008

CDC Reports Tamiflu-Resistant Flu Strain

The Centers for Disease Control and Prevention (CDC) said Friday that a common strain of influenza in the U.S. this winter is resistant to Tamiflu.

In a special advisory to doctors, the agency reported that 49 out of 50 samples tested resist the drug.  Fortunately, they can still be treated with other flu medications.

The situation poses little threat, since Tamiflu is only used in a minority of influenza cases, the CDC said.

"It is still very early in the season. There is very little influenza out there," said CDC Director Dr. Julie Gerberding in a telephone briefing with reporters.

"This is probably actually not going to affect very many people because we don't use a lot of antiviral drugs in our country," Gerberding said. "Most people with influenza don't get any treatment."

In a typical flu season, three strains of flu circulate -- H1N1, H3N2 and influenza B.  It is the H1N1 strain that is resistant to Tamiflu, Gerberding said.  The strain comes mostly from Hawaii, Massachusetts and Texas, the states with the highest number of influenza cases.

Tamiflu, made by Roche AG and Gilead Sciences Inc. and known generically as oseltamivir, can both prevent and treat flu if taken in time. Relenza, a similar drug known generically as zanamivir, is made by GlaxoSmithKline under license from Biota Inc. in Australia.

The CDC recommends that doctors use Relenza or a combination of Tamiflu and a drug called rimantadine if infection with H1N1 is suspected.

However, Terry Hurley, a Roche spokesman, said the CDC's test results were based on a small number of samples from a limited number of states.

"It's early in the flu season and flu is unpredictable. Each flu season is unique. There is no guarantee that this situation will continue throughout the flu season. A lot can change. Last year, for example, the season started with the H1N1 virus and switched to H3N2," he said.

Last year, nearly 11 percent of the H1N1 samples tested were found to be resistant to Tamiflu. Gerberding said she did not believe the virus had evolved, but that the strain that happened to appear was also resistant to Tamiflu.

"We can't predict whether or not these strains will end up being the most important strains in this year's flu season. This particular H1N1 could fizzle out," she said.

According to data from the Health and Human Services Department, the nation's stockpile of antivirals consists of 80 percent Tamiflu and 20 percent zanamivir.  The agency's Dr. Tim Uyeki said this year's development underscores the need to maintain a variety of drugs on hand.

"But zanamivir ... is not approved for those less than 7 years old," Uyeki added.

Those with asthma are also advised against using the drug, which is inhaled.

Gerberding said this year's flu vaccine matched the three strains in circulation very well up to this point.  

In an average year, flu kills roughly 36,000 Americans. The agency said it is not too late for Americans to get a flu shot.  The season typically peaks in February.


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