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Flu Strain Spreading Through US Is Resistant to Popular Treatment

December 22, 2008 12:32 PM
by findingDulcinea Staff
The Centers for Disease Control and Prevention has warned that a flu strain spreading through the United States is resistant to the drug Tamiflu.

Flu Warning

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In a Dec. 19 health advisory, the Centers for Disease Control and Prevention (CDC) issued a warning that a flu strain in the United States is resistant to the popular drug Tamiflu, WebMD reported.

According to Reuters, three strains of flu are common in a normal flu season: H1N1, H3N2 and influenza B. The H1N1 strain prompted the advisory.

Tests showed that 49 of 50 H1N1 samples were resistant to Tamiflu, but the flu strain can be treated with other medications. A drug known as Relenza, or zanamivir, can be used to treat H1N1, as can a combination of Tamiflu and another drug known as rimantadine. However, Dr. Tim Uyeki of the CDC said zanamivir is not approved for children younger than 7.

One reason Tamiflu is popular is that it can be given to children as young as 1.

But doctors said it's still early in the flu season, and the H1N1 strain might not be problematic for long. "There is no crystal ball here," CDC Director Julie Gerberding said in a WebMD article. "We can't predict if this strain will end up being the most important one this year. It could fizzle out."

Gerberding told WebMD that the current flu vaccine protects against all three flu viruses, including the H1N1 strain. There is still time to get the flu shot because flu season generally does not peak before February.

A Whole New Flu Shot

Normally, one or two of the three flu strains targeted by annual vaccines remain part of the vaccine for several years, the Associated Press reports: “Public-health officials make educated guesses on what strains to include, taking into account the strains then circulating in the southern hemisphere.”

This year, for the first time, the process has changed and three totally new strains—two type A viruses called Brisbane 10 and Brisbane 59 that were first isolated in Australia last year and a type B virus first seen in Florida in 2006—will be circulated in the vaccine.

Furthermore, major flu vaccine manufacturers are already shipping the vaccines and plan to have all their doses to health care providers by late October in hopes of alleviating concerns that have arisen with past flu vaccine debacles.

Manufacturers hope the steps will work to create a more successful, more available flu shot. One of the Brisbane strains in this year’s vaccine showed up in the United States after the 2007–08 flu season began, too late to be included in that year’s vaccine, which ended up being only 44 percent effective, compared with 50–90 percent in typical years.

The Centers for Disease Control and Prevention worries that last year’s mismatch will discourage people from getting vaccinated this year, and plans to ramp up its flu vaccine campaign.

Background: The trouble with flu shots

In 2005, distribution and delivery problems left many doctors turning down patients who wanted vaccines until more flu shots came in.

An even more memorable event occurred in 2004, when vaccine manufacturer Chiron distributed 48 million tainted flu shots that had to be discarded, resulting in a major vaccine shortage. The incident raised “troubling questions about how close the tainted flu shots came to being used,” the San Francisco Chronicle reported that October. But more immediately, healthy adults were asked to forgo their flu shots that year, so that the vaccine could go to those most at risk, such as the very young, the elderly and those with certain medical conditions.

But even with improved delivery and potentially better-matched strains, perfecting the flu shot is a difficult matter. Scientists have to make an educated guess about which few flu strains to include in a vaccine every year, even though there are thousands of strains of influenza infecting people around the world at any given time.

Putting every single strain into the vaccine simply isn’t feasible, Slate reported in February: “very few are likely to make someone in the United States sick. Vaccinating people against a disease they’re never going to get is a risky proposition: We don’t know how the body would respond to a barrage of flu vaccinations.”

Reference: Cold and flu guide

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