UPDATE 2-Japan finds first case of H1N1 resistant to Tamiflu

(Updates throughout)

*Patient recovered after treatment with rival drug Relenza

*Both drugs recommended against influenza

By Yoko Kubota

TOKYO, July 2 (Reuters) - Japan has confirmed its first case of a genetic mutation of the new H1N1 flu virus that shows resistance to Tamiflu, the main antiviral flu drug, a health ministry official said on Thursday.

But they said the mutated virus does not appear to be spreading and they see no immediate threat to public health.

They found the drug-resistant virus in a patient who was given Tamiflu to prevent infection but who developed symptoms anyway, the health ministry's Takeshi Enami said.

The World Health Organisation has declared a pandemic is under way from the virus, known as swine flu.

One of the biggest fears is that it will change into a form that resists the effects of the two main antiviral drugs, Tamiflu, made by Switzerland's Roche AG (ROG.VX) and GlaxoSmithkline's (GSK.L) Relenza.

Seasonal flu is no longer affected by older flu drugs and certain strains resist Tamiflu's effects, leaving doctors with fewer options for protecting the most vulnerable patients.

Enami said it was not clear if Tamiflu would have helped the patient, whose age and sex were not given.

The patient was given Relenza and recovered, and does not appear to have infected anyone else.

Kyodo News Agency reported that the patient is a female teacher in her 40s.

Tamiflu, known generically as oseltamivir, and Relenza, known generically as zanamivir, can be used to prevent infection if given early enough. Both can treat flu but Tamiflu is often preferred because it is a tablet, while Relenza must be delivered using an inhaler.

"As of now, we have decided that this does not have a great impact in terms of public health," Enami said.