ZURICH/COPENHAGEN (Reuters) - Scientists have established the first case of the new H1N1 influenza strain showing resistance to Tamiflu, the main antiviral flu drug, Danish officials and the manufacturer said Monday.
It was expected that the strain would at some point show resistance to Tamiflu, Denmark's State Serum Institute said. The patient was now well and no further infection with the resistant virus had been detected.
"It does not constitute a risk to public health and does not cause changes to the recommendations for the use of oseltamivir (Tamiflu)," the institute said in a statement.
The World Health Organization declared an influenza pandemic earlier this month and advised governments to prepare for a long-term battle against an unstoppable new flu virus. The WHO had no immediate comment on the case of Tamiflu resistance.
The United Nations agency has raised its pandemic flu alert to its highest alert level of 6, indicating the first influenza pandemic since 1968 is underway.
Flu viruses mutate regularly and can develop resistance to drugs at any time. The seasonal strain of H1N1 is a distant cousin of the swine flu and was widely resistant to Tamiflu this year.
Common seasonal flu can resist Tamiflu and David Reddy, Roche's pandemic taskforce leader, said a case of resistance in H1N1 -- also know as swine flu -- was not unexpected.
Roche had been working on strategies to counter such a development, Reddy said.
The WHO has said Tamiflu was working against strains of the new H1N1 flu but some analysts have expressed concern it might be less effective than Relenza, GlaxoSmithKline's inhaled drug, since there have been widespread reports of resistance by seasonal H1N1 flu.
Roche stock closed up 1.4 percent at 149 Swiss francs, outperforming a 0.7 percent firmer DJ Stoxx European drugs index.
Surveillance for antiviral resistance in the new strain is continuing, though the isolated case in Denmark does not pose a threat to public health or reason to change recommendations for use of Tamiflu, said David Daigle, a spokesman for the U.S. Centers for Disease Control and Prevention.
"It is well known and expected that influenza virus can mutate spontaneously. The resistance has not changed the capability of the virus to transmit or cause disease, and the assessment is still that this is a relatively mild influenza," Daigle said in an email.
Additional reporting by Paul Arnold in Zurich and Maggie Fox in Washington; editing by Ralph Boulton