WHO Not Worried About Drug-Resistant Pandemic Flu -- Yet

TORONTO, July 8, 2009— -- Public health authorities are reporting three cases of the pandemic H1N1 influenza in which the virus was resistant to a key antiviral drug.

But a top World Health Organization official said he isn't yet concerned about the emergence of widespread, drug resistant strain of the potentially deadly virus.

Until now, all tested strains of the novel H1N1 flu have been susceptible to oseltamivir, known by the brand name Tamiflu, an antiviral drug that can be used to prevent or treat influenza.

But the three cases of a drug resistant virus -- one each in Hong Kong, Denmark, and Japan -- suggest that resistance could arise.

Although most experts say they are not alarmed so far, they note that if widespread resistance to oseltamivir arises, it could take an important weapon out of the hands of doctors.

"Tamiflu has been the main stockpiled drug to be used for treatment and prevention of pandemic influenza, and obviously rapidly developing resistance would be a problem if it were to occur," said Dr. Christopher Ohl, associate professor of medicine at Wake Forest University School of Medicine's Section on Infectious Diseases in Winston-Salem, N.C. "A Tamiflu-resistant virus would not respond to Tamiflu treatment or preventive administration."

What is worrying some is that one of the cases of resistance occurred in a woman in Hong Kong who had not been treated with the drug. In the other two cases, the patients had been given the drug as a preventive measure, according to Dr. Keiji Fukuda of WHO.

Fukuda said the agency is monitoring the situation closely, but no other cases have yet turned up. Moreover, he said, there's no evidence that a resistant strain is beginning to circulate.

"Right now this looks like spontaneous mutation in these patients," Fukuda said at a press conference Tuesday. He said all three patients had the same mutation, and all three had "uncomplicated" disease from which they made full recoveries.

He added there's also no evidence of a resistant strain in any of the contacts of the three patients.