The revisions are based on data from Canada, China, Hong Kong, Singapore and Vietnam, the U.N. agency said. Until now the agency had put the rate at 6-10 percent, although a study earlier this week of patients in Hong Kong said the death rate was around 20 percent.
"The likelihood of dying from SARS in a given area has been shown to depend on the profile of the cases, including the age group most affected and the presence of underlying disease," the health agency said in a statement on its Web site.
WHO also Thursday extended its SARS warning on travel to Taiwan and to two more regions of China.
People planning travel to Taiwan, Tianjin or Inner Mongolia should "consider postponing all but essential travel," said a statement by the U.N. agency.
WHO communicable diseases chief Dr. David Heymann said there were outbreaks of the respiratory disease in those regions, "and we are not able to do the assessments to ensure these areas are safe."
The organization has already issued travel warnings for Hong Kong, Beijing and China's Guangdong and Shanxi provinces.
The death rate from the disease is below 1 percent for people aged 24 or younger, rising to 6 percent for those aged 25 to 44, 15 percent in those aged 45 to 64 and more than 50 percent for those aged over 65.
WHO said studying only those cases where the patient has died or made a full recovery could skew the figures while the outbreak is still continuing because the average time from illness to death is shorter than the average time from illness to recovery.
Its method takes account of the length of time for which patients have survived — looking at the risk of dying in the first week of illness, the risk in the second week, and so on. WHO said this gave a death rate of 14 percent in Singapore and 15 percent in Hong Kong.
In Vietnam, where the outbreak is apparently under control, the death rate was 8 percent. "One explanation for this is the large number of total cases that occurred in younger, previously healthy health care workers," WHO said.
There has been debate for weeks about the true death rate for SARS. It has risen from below 5 percent in the weeks that SARS was first spreading around the globe to a level as high as 15 percent in Canada.
The U.S. Centers for Disease Control and Prevention so far puts the death rate at 6.6 percent.
WHO said the figures only cover those who were sick enough to be admitted to hospitals, not those who recovered at home or who had no symptoms, said WHO communicable diseases expert Dr. Nigel Gay.
"It depends on what you define SARS to be. This is 'severe' acute respiratory syndrome. It's not a case fatality rate for coronavirus infection," he said.
WHO said it also has reviewed the incubation period — the time from exposure to the onset of disease — and continues to conclude that the maximum period is 10 days.
"The incubation period can vary from one case to another according to the route by which the person was exposed, the dose of virus received and other factors including immune status," WHO said.
It said it based its findings on cases in Singapore, Canada and Europe because patients in badly hit areas like Hong Kong and China could have been exposed to the virus on multiple occasions, making it impossible to establish the incubation period.
The study in Hong Kong said that the incubation period could be as long as 14 days. WHO said it would be looking at that in more detail.
If the incubation period is truly longer than 10 days, people who are being quarantined because they have been in close contact with a SARS patient may not be in isolation long enough.
Worldwide, at least 507 people have died from SARS, and more than 7,000 infected.
Meanwhile, China's anti-SARS team has a new member -- NBA star Yao Ming.
The Houston Rockets center plans to host a telethon Sunday in his hometown of Shanghai to raise money for SARS research. His agent, Eric Zhang, says the Shanghai branch of the Chinese Red Cross will accept donations from callers.
Other NBA stars, as well as Chinese soccer and film stars, plan to make videotaped appearances.
The Houston Chronicle reports NBA players Shaquille O'Neal, Allen Iverson, Tim Duncan and Tracy McGrady are sending videotaped messages.