The World Health Organization is looking into reports in Britain and the United States that the H1N1 flu may have developed resistance to Tamiflu in people with severely suppressed immune systems.
Britain's Health Protection Agency (HPA) said five cases have been confirmed in Wales of patients infected with H1N1 resistant to Tamiflu.
The U.S. Centers for Disease Control and Prevention last week also reported four cases of H1N1 resistant to Tamiflu at Duke University Hospital in North Carolina. All were said to be very ill with underlying severely compromised immune systems and multiple other complex medical conditions.