o put this progress in perspective, it is helpful to recall that it took about four years to identify HIV as the cause of AIDS and several more years to delineate and implement the infection control procedures preventing its spread. Two decades after identifying HIV, there still is no effective vaccine.
For all these accomplishments, SARS was a wake-up call about the possibility of another deadly worldwide pandemic. For decades, public health officials have worried about a repeat of the Great Influenza Pandemic of 1918-1919, which killed 20 million to 40 million people. In the United States alone, some 675,000 people died, more than all the American soldiers killed in wars during the 20th Century. Several things were remarkable about the 1918-1919 pandemic. It had an incredibly high death rate and, even more worrisome, it killed rapidly. People who were healthy one day were dead the next. And most concerning of all, its victims were not only the elderly and immune compromised, but the young and otherwise healthy.
Initially, concerns about SARS intensified when it was realized that the virus was potentially much more deadly than the 1918-19 flu virus. Approximately 11 percent of all known SARS patients died, and among the elderly the figure was 50 percent. Fortunately, SARS turned out to be a near miss and the epidemic burned out over the summer of 2003. It infected an estimated 8,422 people and left 916 dead in 29 countries. The happy ending of our first meeting with SARS can be attributed to a combination of intense public health control efforts and to the virus' poor ability to spread.
Nevertheless, the SARS epidemic taught us at least four key lessons.
First, SARS emphasized that the real pandemic threat is likely to be a combination of a highly infectious respiratory virus and the global transport infrastructure. Because respiratory viruses are spread by breathing, coughing and touching, they can infect hundreds and thousands of people much more easily and rapidly than viruses spread by sex or contact with blood. With today's extensive global transport of people and goods by air and sea, a virus can spread widely before anyone notices.
Second, SARS, like pandemic influenza, HIV and other deadly viruses, seems to originate in animals, and then for mysterious reasons mutates and jumps to humans. Therefore, we need to focus more research on animal infections and on the surveillance of novel epidemics among animals.
Third, certain public health interventions work and others don't. SARS taught us about the damage that can be done by trying to hide information. For months, China hid its outbreak of pneumonia. Earlier action might have avoided the global outbreak of SARS. The outbreak also emphasized the need to strengthen early warning systems for tracing the spread of viruses, and the apparent effectiveness of "old-fashioned" disease control measures, such as isolation and quarantine.
Most important, SARS reminded us of the need for global cooperation on health and research. Globalization means the health of other countries affects us. Improving the infrastructure of housing, health care and public health in developing countries is going to be key to combating emerging infections. If we are not moved by the suffering of the world's poor to help, then at least self-interest should motivate us to improve their living conditions and health care, otherwise we risk dying of their infections.
This winter we will need vigilance until we are sure that SARS or some other deadly respiratory virus will not return with the cold weather. Public health officials and hospitals worldwide will have to be on their toes to detect new viruses among a sea of "flulike" illnessesIf we succumb to the urge to move on and ignore the lessons of SARS, we will increase the risks and harms of the next great pandemic.