The WHO said that it was still gathering global data about "an increased number of (seasonal) H1N1 viruses with resistance to oseltamivir" following the first reports which emerged in Europe in late January.
GENEVA (Reuters) - Australia and Hong Kong have joined North America and parts of Europe in reporting seasonal influenza viruses with increased resistance to the antiviral drug Tamiflu, the World Health Organization said on Thursday.
The WHO said that it was still gathering global data about "an increased number of (seasonal) H1N1 viruses with resistance to oseltamivir" following the first reports which emerged in Europe in late January.
Oseltamivir is the generic name for Tamiflu, made by Switzerland's Roche Holding AG and Gilead Sciences Inc of the United States, which governments worldwide have been stockpiling as a first line of defense in case the bird flu virus sparks a human influenza pandemic.
The mutated H1N1 showing resistance is a sub-type of ordinary influenza A, different from the H5N1 virus which causes bird flu. But the resistance to Tamiflu has raised questions about its potential effectiveness in a deadly bird flu pandemic.
!ADVERTISEMENT!Spokeswoman Sari Setiogi said that for now the WHO was not changing its recommendation that Tamiflu be used to treat seasonal flu.
"We still expect to see more testing be done," she said.
In Hong Kong, 5 of 67 samples of the H1N1 virus tested, or 7 percent, showed resistance to Tamiflu, according to a WHO table. In Australia the rate was 2 out of 36 samples, or 6 percent.
In Japan, where Tamiflu is widely prescribed for seasonal flu, none of the 71 samples tested showed resistance, WHO said.
A week ago, the WHO reported that the main seasonal virus circulating in both Canada and the United States showed "elevated resistance" to Tamiflu. These rates are 6 percent and 8 percent, respectively, according to the WHO's latest figures.
A preliminary survey issued by the European Centre for Disease Control (ECDC) last month 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.
According to WHO's latest figures, seasonal flu viruses from five countries in Europe have shown double-digit resistance to Tamiflu -- Norway (70 percent), Portugal (33 percent); Finland (29 percent), France (17 percent) and Denmark (10 percent). In several of these countries, fewer than 10 samples were tested.
Sweden, Germany and Britain showed resistance rates of 8, 7 and 5 percent, respectively. Some European countries reported no resistance at all, including Italy, Spain and Switzerland.
Past studies had found Tamiflu resistance rates ranging from zero to 0.5 percent, according to the United Nations agency.
No countries in Africa, Latin America or the Middle East have yet reported their findings to the 193-member state WHO.
Roche spokeswoman Martina Rupp said more data was needed "to establish the geographic distribution of the virus and evaluate the potential impact of effectiveness of drug use."
"What is important is that the mutation has only been seen in H1N1, not in avian strains," she said from Roche's Basel headquarters.
(Reporting by Stephanie Nebehay; Editing by Richard Balmforth)
