Fri, Feb 01, 2008 - Page 6 News List

Scientists surprised by influenza virus resistant to Tamiflu


A small but significant percentage of the main influenza virus causing illness this winter in Europe, Canada and the US has a mutation that makes it resistant to the anti-influenza drug Tamiflu, the WHO said on Wednesday.

Scientists said they were surprised by the finding because they had believed that mutations of this type generally made the virus less potent and less easily spread among people. The predominant influenza virus circulating this winter is influenza A/H1N1.

The Tamiflu-resistant form of the virus, known as influenza A(H1N1 H274Y), has been found with varying frequency in various areas of four European countries, Canada and the US.

There are no immediate plans to recommend changes in the use of Tamiflu, which is also known as oseltamivir, officials from WHO and the US said in interviews, because the incidence of the mutant virus is still small. Tamiflu is one of the antiviral drugs used to treat influenza in its early stages.

Nevertheless, officials from WHO, a UN agency, said they were troubled by the discovery.

"Clearly, this is of global concern, but it is not a global problem now," Dr Frederick Hayden, an influenza expert at the organization, said in a telephone interview.

The standard influenza vaccine still protects against the mutant virus, said Hayden and Alicia Fry, an influenza epidemiologist at the US Centers for Disease Control and Prevention.

Norwegian epidemiologists first called attention to the problem last week when they reported that the mutation was present in 12 of 16 of viruses isolated in that country from patients in the earliest part of the influenza season, in November and December.

The Norwegian rate was the highest among the four European countries -- Britain, Denmark, France and Norway -- that reported the mutant virus. There was no evidence that the 12 cases in Norway were linked.

Overall, the mutant form was found in 19 of the viruses isolated from 148 patients or 13 percent, in a monitoring system that the European Center for Disease Prevention and Control runs in 10 European countries.

The overall percentage fell to 5 if Norway was excluded.

In the US, the Tamiflu-resistant strain was found in 9 of 237, or 3.8 percent of patients from whom influenza type A and B viruses were isolated this winter, and all 9 were in the A(H1N1) category, making them 6.7 percent of those 135 cases, Fry, said in a telephone interview.

The WHO conducted a teleconference on Tuesday to collect information from experts in a number of countries. The participants agreed that continued close monitoring was needed to collect information on a larger number of patients to determine the frequency, transmission and distribution of the mutant strain as well as its virulence, Hayden said.

Scientists also want to learn how the resistance developed. It is unlikely to have been from use of Tamiflu, Hayden said, in part because no cases have been detected in Japan, where the drug is often used in treatment.

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