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, Reuters quoted the World Health Organisation as saying today. 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. Pregnant women, children under the age of 2 and people with respiratory problems and other diseases are at highest risk of the extreme effects of swine flu, which can take hold as soon as one week after infection by the highly contagious virus. "The window of opportunity is very narrow to reverse the progression of the disease," Shindo said. "The medicine needs to be administered before the virus destroys the lungs." The new clinical guidelines also recommend that people outside the at-risk group who have "persistent or rapidly worsening symptoms," such as problems breathing or a high fever for more than three days, should take antivirals. These should be administered by a doctor, and are not needed by people who have only a typical cold, Shindo stressed.