President Bush on Friday gave federal health officials authority to quarantine Americans sick with the highly contagious new mystery illness. Officials said there were no immediate plans to use the emergency powers.

In an executive order signed Friday, Bush added severe acute respiratory syndrome, or SARS, to the list of diseases for which health authorities have authority to hold Americans against their will.

It's the first time a new disease has been added to the list in two decades.

"If spread in the population," the order says, SARS "would have severe public health consequences."

Several diseases have long been on the list for which quarantine may be used: cholera, diphtheria, infectious tuberculosis, plague, smallpox, yellow fever and several viral hemorrhagic fevers.

Also Friday:

-- Federal researchers said they are beginning work toward a vaccine that could eventually help control SARS. They are already courting private pharmaceutical companies that might manufacture the treatments down the road.

-- In China, officials issued an extraordinary apology for not doing a better job of informing people about SARS. U.S. Secretary of Health and Human Services Tommy Thompson said he spoke with his counterpart in China and they pledged to cooperate in battling the outbreak.

-- Investigation into the disease's origins continued. International health officials were seeking the first person believed infected with SARS, a man in the hard-hit southern province of Guangdong.

SARS, whose symptoms include fever, aches, cough and shortness of breath, has killed at least 85 people in Asia and Canada and sickened at least 2,300 in more than a dozen nations as infected travelers spread the disease. In the United States, 115 cases in 29 states have been reported.

About 4 percent of the victims have died from the disease, though none of them in this country. There's no cure yet, but most sufferers are recovering with timely hospital care.

While U.S. authorities described the executive order as a precautionary measure, quarantine has been used in other nations fighting SARS. In Hong Kong, authorities used barricades and tape to seal 240 people inside their infected apartment building, and the next night, they were put in quarantine camps.

In Ontario, anyone with symptoms, anyone who has been in contact with SARS patients or anyone who visited two hospitals where the illness first turned up were asked to quarantine themselves at home for 10 days.

And in Singapore earlier this week, authorities ordered the men's and women's rugby teams to quarantine themselves at home for at least a week after they returned from the Hong Kong Sevens tournament.

Asked about actions abroad, Secretary of Health and Human Services Tommy Thompson said Tuesday that such measures didn't yet appear warranted in the United States.

"If there is a virus that is explosive ... and the only way to control it is by quarantine, we have to consider it," he said. "But we're not there yet."

Legally, quarantine involves restricting the movement of healthy people who may have been exposed to an infectious disease and may be carrying it. It's almost always done voluntarily, and usually for only a short period of time, Dr. Julie Gerberding, director of the Centers for Disease Control and Prevention, said this week.

Quarantine might be used, for instance, while someone is being treated, she said.

"It's very important to move away from the understanding of quarantine that we had a century ago, which was really something that was ... often very unfair and very difficult for the people who were involved in it. That is not the kind of quarantine that we're talking about in the 21st century," she said. "We're talking about public health tools that simply serve to protect people or to protect themselves or others from a communicable disease."

Isolation, a related but less severe action, involves separating people who are known to be infected from others. It is usually voluntary and occurs frequently in hospitals.