What You Need to Know About Drug-Resistant Flu

This year's flu season is off to a slow start, but health officials are watching a disturbing development that could make treating the flu even more difficult if you do catch the bug. The Centers for Disease Control and Prevention (CDC) reported in the fall that the most common strain of flu now making the rounds in the U.S. is resistant to oseltamivir, or Tamiflu, the most popular antimicrobial used to treat influenza. But that doesn't mean a pandemic is necessarily on the way. Here's why.

Related

Health

The Year in Medicine 2008: From A to Z

Stories

• Does the Flu Vaccine Really Protect Kids?
• How Long Does Flu Immunity Last?

1. How did the flu virus become resistant to Tamiflu?

Health officials have been tracking the strain in question since the last flu season, when the CDC reported that 11% of flu cases were resistant to Tamiflu. According to Dr. Joseph Bresee, chief of the epidemiology and prevention branch of the CDC's influenza division, experts believe the resistant strain is the result of a spontaneous mutation in the influenza virus genome and not the result of overuse of antimicrobial agents like Tamiflu to treat the infection. That's based on the fact that during the last flu season, the resistant strain was widespread in countries with low Tamiflu use like Norway but less common in places like Japan where reliance on Tamiflu is high. (See Dr. Sanjay Gupta's Fit Nation column.)

2. Who is most at risk of getting infected with this resistant strain?

Anyone can catch the flu, and the CDC recommends that everyone who wants to be protected should get vaccinated. The agency reports that there is plenty of flu vaccine available. The current vaccine is designed to offer some protection against the Tamiflu-resistant strain.

3. Do vaccinated people still need to worry about this flu strain?

Because there are many circulating strains of flu and no flu vaccine is 100% effective, you may still get sick even after getting a flu shot. If you are infected with the resistant strain, then Tamiflu will not relieve your symptoms.

4. If Tamiflu doesn't work, then what else can I take for flu?

Another antimicrobial, zanamivir, or Relenza, is still effective against the circulating Tamiflu-resistant strain. However, that drug, which is an inhaled powder, is not recommended for children under 7, for whom a combination of Tamiflu and an older drug, rimantadine, can be used to control the infection. Since every flu infection is made up of three different types of influenza virus, both Relenza and rimantadine still work to disarm the two types that are not resistant to Tamiflu.

5. Does this flu strain make people more susceptible to avian flu?

No. It's unlikely that the two flu strains are related other than that both are the result of mutations in the influenza virus genome.

See TIME's Pictures of the Week.

See the Year in Health, from A to Z.