The World health Organization has announced that the main flu virus currently infecting people in Canada and the United States is showing an un expected elevated resistance to Tamiflu.
The World Health Organization has issued a statement that advises that the main flu virus circulating in the United States and Canada is showing elevated resistance to the antiviral drug Tamiflu.
According to the CTV
report, in Canada, 8 out of 81 samples showed resistance -- more than a 10 per cent resistance rate. Just less than 1 per cent of flu viruses are normally expected to be resistant to the drug.
"These preliminary data indicate that oseltamivir resistance in H1N1 viruses is geographically variable but not limited to Europe," the WHO said in a statement.
In the United States, the U.S. Centers for Disease Control and Prevention have reported a five per cent rate of resistance to Tamiflu in samples of H1N1 virus tested to date.
In Europe, the European Centre for Disease Control is reporting that flu viruses resistant to Tamiflu, known generically as oseltamivir, have been found in nine of 17 European countries.
Of the H1N1 flu viruses that have been checked approximately 14 per cent have carried the resistance mutation, which has been shown in testing to dramatically reduce a virus's susceptibility to the drug, the agency 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.
To date there is no evidence that the resistant viruses are causing more severe illness than other influenza viruses.
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 flu, nor Hong Kong has seen increased resistance.
The viruses that were tested in Europe were from the early part of the flu season and it is possible the pattern might have shifted since then, or the situation may worsen as the flu season continues.
"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.
"Influenza viruses are continuously changing and it is possible that a resistant strain has emerged spontaneously. Further detailed laboratory characterization of circulating H1N1 viruses and epidemiological information on patients will be needed to help answer this question."
The resistance mutation has been found almost exclusively in viruses that were collected from people who had not taken Tamiflu. It may therefore be possible that the drug may be more vulnerable to the development of resistance than initially believed.
Tamiflu is generally seen to be the main medication for treating H5N1 bird flu in humans.
There is also a proposal that it be used as the main defence in the event that that virus, which now mainly affects poultry, mutates into a form that spreads easily among people.
