WHO reports Tamiflu-resistant flu in U.S., Canada

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WHO reports Tamiflu-resistant flu in U.S., Canada

By Nebehay Fri Feb 1, 1:44 PM ET

GENEVA (Reuters) - The main seasonal flu virus in the United States

and Canada as well as parts of Europe shows higher resistance to the

antiviral drug Tamiflu, raising questions about its potential

effectiveness in a human bird flu pandemic.

The World Health Organization (WHO) reported the elevated resistance

in North America on Friday, but said it was too early to know what the

chances may be for increased Tamiflu resistance in the H5N1 strain of

avian influenza.

It did not change its recommendation that Tamiflu be used to treat

human cases of bird flu.

A number of governments have been stockpiling Tamiflu, made by

Switzerland's Roche Holding AG and Gilead Sciences Inc of the United

States, for use as a first line of defense in case bird flu sparks a

human influenza outbreak.

Health experts fear that the virus, which now mainly affects poultry,

could mutate into a form that spreads easily among people and trigger

a deadly pandemic.

The WHO said it was investigating the extent of resistance worldwide

to Tamiflu, known generically as oseltamivir, in some seasonal H1N1

flu viruses that have a mutation making them " highly resistant. "

" The frequency of oseltamivir resistance in H1N1 viruses in the

current influenza season is unexpected and the reason why a higher

percentage of these viruses are resistant is currently unknown, " the

WHO said.

The U.S. Centers for Disease Control and Prevention has reported a

five percent prevalence of resistance to Tamiflu in samples of H1N1

virus tested. In Canada, 8 out of 128 samples showed resistance,

roughly 6 percent, WHO spokeswoman Hartl said.

" These preliminary data indicate that oseltamivir resistance in H1N1

viruses is geographically variable but not limited to Europe, " the WHO

said in a statement.

A preliminary survey issued by the European Centre for Disease Control

(ECDC) this week said that of 148 samples of influenza A virus

isolated from 10 European countries during November and December, 19

showed signs of resistance to Tamiflu.

The mutated H1N1 is a sub-type of influenza A.

Of 16 samples from Norway, 12 tested positive for resistance against

Tamiflu, according to the ECDC study.

The new " elevated resistance to oseltamivir " appears limited to

seasonal H1N1 viruses, and does not involve H3N2 or influenza B

viruses which are also circulating, the WHO said.

" This means that oseltamivir would most likely be ineffective for

treating or preventing infections caused by these resistant H1N1

strains, although the drug will be effective against other influenza

virus infections, " it added.

The WHO said it was contacting national health authorities to

determine the extent of resistance to the drug. Neither Japan -- where

Tamiflu is widely prescribed for seasonal flu -- nor Hong Kong had

seen increased resistance to date, it said.

" It is still early in the (seasonal flu) season, we don't have a full

picture yet, " Hartl said.

Past studies had found Tamiflu resistance rates ranging from zero to

0.5 percent, according to the U.N. agency.

http://news./s/nm/20080201/hl_nm/tamiflu_resistance_who_dc_5