UPDATE 1-UK investigates spread of drug resistant swine flu

(Adds details and reaction)

* Five H1N1 patients resistant to Tamiflu

* Possible person-to-person spread of resistant strain

LONDON, Nov 20 (Reuters) - British health officials are investigating the likely person-to-person spread of a drug-resistant strain of swine flu, the Health Protection Agency said on Friday.

There have been five confirmed cases in Wales of patients infected with H1N1 resistant to oseltamivir -- the generic name of Roche AG ROG.VX and Gilead Sciences Inc's GILD.O antiviral drug Tamiflu, the agency said.

Four other patients are infected with H1N1 with the same genetic mutation but one was helped by Tamiflu and the status of three others is not clear. Another antiviral, GlaxoSmithKline GSK.L and Biota Inc's BTA.AX Relenza, was effective in the patients, the HPA said.

The patients had serious conditions that suppressed their immune systems, which can give the virus a better than usual opportunity to develop resistance, the HPA added.

“Although further epidemiological investigation is underway, it would seem likely that transmission of oseltamivir-resitant H1N1 virus has taken place,” it said in a statement. “At present we believe the risk to the general healthy population is low.”

John McCauley of the Medical Research Council said the patients involved were in an at-risk group.

“It is well established that patients with immunodeficiency do have problems with eliminating virus, giving it a greater chance to acquire resistance,” he said in a statement.

The World Health Organisation has reported 57 cases of Tamiflu resistance worldwide. There have not yet been any confirmed cases of person-to-person transmission, although a possible case in the United States is under investigation.

The British government launched a national pandemic flu service in July to allow people to get a diagnosis and prescription online or over the phone without visiting a doctor.

It said on Friday it was taking the development of a Tamiflu-resistant strain seriously but it would continue to offer the antiviral to all patients.

“Our strategy to offer antivirals to all patients with swine flu is the right one, to help prevent complications and reduce the severity of the illness,” the Department of Health said in a statement.

British officials have confirmed the H1N1 virus has killed 214 people, but experts note that most people who are made sick by the virus are not tested.

A nationwide vaccination programme began last month, initially targeting those considered high risk, such as pregnant women and front-line healthcare workers.

Norwegian health authorities reported a mutation of H1N1 in some patients with severe disease but other officials noted quickly that other patients infected with the same mutant have had mild disease. [ID:nLK669768] (Reporting by Kylie MacLellan; editing by David Stamp)