Published: 7:40PM BST 29 Jun 2009

A patient who had been in direct contact with a person suffering from the new H1N1 influenza strain was given a dose of Tamiflu as a preventative measure.

But she still contracted the virus
after her body resisted the treatment leading doctors to give her another type of medication, Relenza, made by GlaxoSmithKline, the British pharmaceutical company.

The Danish national is no longer suffering from the illness and is not displaying symptoms, the Danish Institute of Serology said in a statement.

"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.

A spokesman for the Swiss company Roche, which manufactures Tamiflu, said the patient's resistance was likely to be an individual case.

David Reddy, Roche's pandemic task force leader, said the case was within the 0.5 per cent rate of case resistance to Tamiflu that had been established in clinical trials.

The World Health Organisation declared an influenza pandemic earlier this month and advised governments to prepare for a long-term battle against an the 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 under way.