A Cautionary Tale  pg. 3

While the global press has latched on to potential bioterrorism agents like smallpox and anthrax, experts in virology have warned that the next great pandemic, or worldwide outbreak, most likely will be an influenza. “In many ways flu is the scariest disease there is,” says Edwards. “In contrast to AIDS, where you have to exchange blood or some sort of secretions, flu you get by what you breathe. It’s respiratorally spread, and in a moment a virus that’s in a pig lot in China can suddenly be in Los Angeles—and then all over the country.”

One of the most devastating pandemics of all time was the 1918-19 flu, which killed 500,000 people in the United States and over 20 million worldwide. The greatest death toll was among healthy young adults. An accepted theory is that the pandemic was caused by the movement of troops during World War I, but Peter Wright, M.D., former head of Vanderbilt’s Pediatric Infectious Diseases division, believes the answer may not be that simple. “The pandemic occurred equally in women,” he explains. “And I had occasion to look at the public health records in Iceland, and the same pattern of deaths occurred in Iceland, which was pretty isolated from the effects of World War I.”

Depending on a population’s level of immunity to a particular strain and to subtle changes that occur in a virus’ makeup, he says, influenza has a capacity to be more or less virulent and more or less deadly. Influenza virus types A, B, and C are classified based on the antigenic differences between two surface glycoproteins, H and N—hemagglutinin, which facilitates entry of the virus into host cells, and neuraminidase, which assists in the spread of infection. To illustrate just how insidious these antigenic changes can be, the 2003-04 vaccine contained protection against the H3N2 Panama-A strain, but not against its noxious H3N2 Fujian-A cousin that emerged too late to be included in doses manufactured for the season.

Most of the flu viruses that are emerging today originate in China and areas of the Far East where crowded, open air, poultry and meat markets create a prime breeding ground for viruses found in fowl and other animals including civets, small mammals that have been linked to SARS. These viruses constantly reassort and recombine their genes, creating new strains, some of which are pathogenic to humans. If influenza’s surface proteins were as stable as mumps or rubella’s, for example, one vaccine would offer lifetime protection. Instead, flu strains mutate quickly and unexpectedly, and antibodies against one strain don’t necessarily provide immunity to the next year’s outbreak. Public health officials, under the aegis of the World Health Organization and the National Institutes of Health, meet annually in Geneva to evaluate which pathogens are appearing on the scene, and to commit to developing vaccines for the upcoming crop of viruses. In other words, getting a good flu vaccine in any given season is like shooting a moving target.