The World Health Organization has warned doctors to brace for a possible wave of very sick H1N1 swine flu patients.
The U.N. health agency said Friday the virus can cause life-threatening viral pneumonia that may be particularly dangerous to otherwise healthy young people.
Health officials urged doctors to treat suspected cases quickly with antiviral drugs.
The warning comes as U.S. health officials announced deliveries of swine flu vaccines will be delayed. The Centers for Disease Control and Prevention says there will only be 28 million to 30 million doses of the vaccine available by the end of October instead of a projected 40 million.
The CDC says there is wide spread flu activity in 41 U.S. states, an unprecedented level for this time of year. They say for the first week this fall, the level of influenza and pneumonia mortality in the U.S. is above the epidemic threshold.
The WHO has declared the swine flu outbreak a pandemic. The agency says more than 4,700 deaths attributed to H1N1 influenza have been reported worldwide.