Will SARS Strike Here?

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Mild cases would also act like natural vaccines, conferring immunity on the patients. When 70% or so of a population has immunity — what epidemiologists call herd immunity — a virus is considered burned out: it can't spread further because there is almost no one left to infect. In the meantime, hospitals are trying to prevent the disease from taking root by isolating patients and religiously using gowns, masks, goggles and gloves — techniques that so far have proved extremely effective at preventing transmission.

Still, although the number of new cases in such hot spots as Singapore and Hong Kong finally began to drop last week, nobody is prepared to say that this outbreak is even close to being over, especially considering that many residents of Hong Kong's Amoy Gardens apartments fled before officials could arrive to take them into quarantine. "I don't want to give anybody a false expectation that this is under control," says Ostroff. "This is still a very fluid situation."

So while public-health officials stay on high alert for any new cases, researchers are trying to erase any lingering uncertainty about the ultimate cause of SARS. Several kinds of diagnostic tests are nearly ready. A vaccine against the coronavirus is already under development. And epidemiologists in Asia, Europe and North America are piecing together the natural history of SARS. That last effort should be made a lot easier with the Chinese government's decision last week to finally let a WHO team into Guangdong. Medical detectives may have already found the very first recorded victim — patient zero — a man in the city of Foshan who passed the virus on to four people before he recovered.

Even if all these measures fail to eliminate SARS quickly or completely, they should at least minimize the danger. "People should be concerned," says Ostroff. "But I don't think they should be alarmed." The minuscule murderer in Dr. Nicholls' microscope sights is still potentially deadly. But it no longer looks like the monster it appeared to be just a few weeks ago.