UPDATE 2-Antivirals can prevent pandemic flu deaths - WHO

* U.N. agency changes recommendations for treating flu

* Antivirals urged for sick pregnant women, young children

* Can avert severe pneumonia and deadly complications

(Recasts with details of changed recommendations, fresh quotes)

By Laura MacInnis

GENEVA, Nov 12 (Reuters) - Antiviral medicines can prevent H1N1 flu deaths and should be given quickly to pregnant women, very young children and people with underlying medical problems who fall ill, the World Health Organisation said on Thursday.

Announcing a change of its guidance to doctors, the United Nations health agency said the drugs should be administered even before tests conclude that an at-risk patient has the pandemic virus and not something else.

"We have updated our clinical guidance to emphasise that seeking early medical attention can save lives," Nikki Shindo of the WHO's global influenza programme told journalists on a teleconference.

The H1N1 strain, which the WHO declared a global pandemic in June, can cause severe pneumonia in previously healthy people. It has killed more than 6,000 people and spread to 199 countries since its discovery in North America earlier this year.