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Another factor scientists do not understand is the superspreader, a person who appears to pass the disease on with extraordinary efficiency. Part of the explanation may be in the individual's genetics. "We don't know what those genetic factors are yet," says Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases (NIAID), "but they're not necessarily related to how sick the person is." Some experts suspect that superspreaders might have a more virulent strain of coronavirus or be co-infected with other microbes. Having multiple infections may, these scientists speculate, increase one's chance of passing on the disease.
The risk of death from SARS, meanwhile, may have less to do with a particular strain of the virus and more to do with the body's reaction to it. "The immunological and inflammatory response of the body," says Fauci, "could be contributing significantly to the damage in the lungs." But nailing that down, along with questions of whether survivors become immune to further infection and whether the disease is permanently with us, like AIDS, will take more research.
So will the search for a vaccine. The biotech company GenVec announced plans last week to collaborate with NIAID to insert portions of the coronavirus genome into a weakened cold virus. If the proteins generated by these snippets are powerful enough to trigger an effective immune response, then the resulting vaccine might be successful. NIAID is also coordinating separate U.S. government efforts to develop vaccine candidates. And the U.S. Army Medical Research Institute for Infectious Disease is screening thousands of compounds to see if any might slow or stop the disease.
--WILL IT BREAK OUT HERE?
With any luck, SARS won't hit the U.S. hard until some of these loose ends are tied up. Airlines have handed out more than 500,000 yellow health-alert cards from the CDC that tell passengers arriving from SARS-prevalent areas what symptoms to be alert for and whom their doctors can call; the CDC has also posted on its website detailed information for health-care workers.
But that may only put off the inevitable. While the U.S. is better equipped than most countries to detect and contain epidemics, it's pure luck that it has not been hit harder. So far, none of the handful of people who have carried the virus to the U.S. from Asia have been superspreaders. And health-care workers in the U.S. have not yet made any of the mistakes that tripped up the Canadians: a patient transferred from an affected hospital to an unaffected one, lax enforcement of isolation orders, hospital workers who may not have been vigilant enough with protective gear.
The more time that passes, the better the U.S. can learn from the experience of other countries. But as long as there are even small pockets of infection lingering anywhere in the world, an outbreak is always a threat. In a world as interconnected as ours, it may just be a matter of time before SARS strikes in the U.S. the way it has elsewhere. "It's too soon to count our chickens," says Fauci. "This is an evolving epidemic, and we need to take it very seriously." --Reported by Steven Frank and Daffyd Roderick/Toronto, Matthew Forney/Guangzhou and Susan Jakes and Huang Yong/Beijing