The first H1N1 infection found to be resistant to the antiviral drug Tamiflu represents an isolated case with no current implications for public health, the World Health Organization (WHO) said on Tuesday.

The United Nations agency has declared a global pandemic is underway from the virus known as swine flu which has so far been treatable with Tamiflu, made by Roche.

WHO spokesman Dick Thompson said that the discovery of a patient in Denmark whose infection did not respond to the drug, revealed by the Swiss company and Danish officials on Monday, did not amplify the severity of the virus.

This is an isolated case. At this time, there is no public health implication. But we must remain alert as the virus can change at any time and we must not be complacent, he told Reuters.

Officials say the patient is now well and no further contagion with the resistant virus was detected.

Resistance to Tamiflu has been previously documented in the deadly bird flu virus H5N1 and seasonal H1N1 flu, Thompson said.

We need to monitor the virus (H1N1) continuously, he said, adding that the WHO's global influenza surveillance network linking laboratories in 97 countries would keep monitoring it.

WHO is not changing its recommendations for the use of antivirals, Thompson added, referring to the global body's advice to its 193 member states.

The WHO has previously said that the H1N1 virus is sensitive to a class of antiviral drugs which includes Tamiflu, known generically as oseltamivir, and Relenza by GlaxoSmithKline, known generically as zanamivir.

Denmark's State Serum Institute said, when making the announcement on Monday, that it was expected that the strain would at some point show resistance to Tamiflu.

It said that while the patient was found to be infected with a virus strain that had mutated to a form resistant to Tamiflu, the alternative drug Relenza, which is inhaled, remained an effective treatment.

GLOBAL PANDEMIC

The WHO on June 11 raised its pandemic flu alert to its highest level of 6, signifying that the first influenza pandemic since 1968 was under way [ID:nLC321991]

Flu viruses mutate regularly and can develop resistance to drugs at any time.

The WHO has said Tamiflu was working against strains of the new H1N1 flu but some health experts have expressed concern that it might be less effective than Relenza, since there have been widespread reports in the past year of resistance to Tamiflu by seasonal H1N1 flu, a distant cousin of the new swine flu virus.

David Daigle, a spokesman for the U.S. Centers for Disease Control and Prevention, said that the isolated case in Denmark did not merit a change in the recommended use of Tamiflu.

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, he said on Monday.

At least 20 companies make flu vaccines, including Novartis, Sanofi-Aventis, GlaxoSmithKline, Baxter International, Solvay, Australia's CSL and nasal spray maker MedImmune, now part of AstraZeneca.

French drugmaker Sanofi-Aventis, which has estimated it makes 40 percent of the world's supply of flu vaccine, said this month that it had begun large-scale production of a H1N1 vaccine through its Sanofi-Pasteur unit.

Novartis has said it expects a vaccine to be available by autumn and Baxter International has said it is in full-scale production of a vaccine that could be ready for commercial use as early as July.

Glaxosmithkline Medicine