Resistant Flu Virus Detected in Europe

European health officials have detected flu viruses resistant to Tamiflu in over a dozen European countries. The resistant strains most likely emerged elsewhere, but were first identified in Europe.

Typically, only about 1 percent of H1N1 flu viruses are resistant, but this year the data shows that 13 percent of the viruses are resistant to Tamiflu.

Resistance varies from country to country, with Italy reporting no resistant strains, and Britain, France and Denmark all reporting low but significant percentages.

The highest levels are in Norway, where nearly 70 percent of tested strains have been resistant.   Health authorities are currently working to find out how prevalent the resistant strain is worldwide.

Fred Hayden, a World Health Organization (WHO) flu expert, told Associated Press, “It’s an unexpected finding and a signal worth watching."

A single mutation is responsible for the strain’s resistance.  The mutated virus can still be treated with other antivirals, and it does not cause a more serious case of flu than the non-resistant viruses.  However, doctors worry that if the resistance becomes widespread, Tamiflu could become a useless tool against the flu.

"If I had only a single drug to choose for influenza, oseltamivir (Tamiflu) is the one I would go for," Dr. Angus Nicoll, influenza coordinator for the European Centre for Disease Prevention and Control, told AP.   

The WHO has stockpiled Tamiflu in various countries around the world for possible use in a flu pandemic.

However, some experts have warned against relying exclusively on Tamiflu. "This is a very good reminder that we don’t know what the next pandemic strain will be sensitive to," Nicoll said. "Perhaps we should have more mixed antiviral stockpiles."

Authorities say the mutated H1N1 flu virus should not be confused with a mutation of the H5N1 bird flu virus.   

"The chance of this happening in an H5N1 virus is not zero, but probably very rare," said Dr. Joseph Bresee, chief of epidemiology and prevention at the U.S. Centers for Disease Control and Prevention. Two Tamiflu-resistant H5N1 strains have been found in Asia during the past few years.

In the United States, nearly 3 percent of tested flu samples have been Tamiflu-resistant. "We don’t know right now if this is a trend on the upswing or just a small blip," Bresee said. Usually, resistant strains arise in people who have been treated with Tamiflu, but that is not the case here.

In Norway, none of the viruses were from people who had been treated with Tamiflu. And in Japan, where Tamiflu use is the highest in the world, no resistant viruses have been reported this year.   

Investigations are ongoing in other countries.

Scientists worldwide are working to sequence the mutated virus to determine its origin and learn how it developed.  Until now, experts believed that if viruses developed resistance, they would be less transmissible.  "That assumption appears to have been incorrect," Hayden told AP.

As Europe and North America begin their flu seasons, doctors and scientists will be monitoring any potential spread of the resistant strains.

For now, public health agencies say their recommendations on Tamiflu use remain unchanged.

“It’s still too early to know for sure what this means," Nicoll said. "But watch this space."

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