Cold, Flu, & Cough Health Center

Bird Flu Threat Rises

Killer Flu Pandemic: What Could Happen?

The H5N1 bird flu virus could, theoretically, become a pandemic flu virus overnight. That could happen if a person or animal were infected with a human flu virus and the bird flu virus at the same time. In that case, the viruses could "reassort" -- that is, swap genes.

On the other hand, what seems to be happening is that the H5N1 virus is only gradually learning how to pass more easily from human to human. That, Stöhr says, is giving us time to prepare. But when the virus does learn this trick, it's going to be hard to stop.

This last happened in 1968, when a new human flu virus appeared in Asia. It took six to nine months to reach the U.S. Today, it would probably take only three months.

Right now, the world has only 2 million doses of a new vaccine against H5N1 bird flu -- all in the U.S. Safety tests aren't yet complete. And it's not even clear whether the vaccine will really work against the strain of flu that eventually emerges.

Although the bird flu virus is extremely deadly to humans, it's likely that it would become less virulent if it adapted for human-to-human spread. But it could easily be as deadly as the worst flu virus yet: the pandemic flu of 1918 that killed 50 million people worldwide -- half of them young, healthy adults.

So what might happen? Michael T. Osterholm, PhD, MPH, is director of the Center for Infectious Disease Research at the University of Minnesota. He sketched out a likely scenario in the May 5 issue of The New England Journal of Medicine.

Osterholm notes that with current technology, it would take at least six months to start producing a vaccine -- and two doses would be needed for protection. And as Stöhr notes, the virus would reach the U.S. within three months.

If the bird flu started a pandemic now, Osterholm wrote:

"We would be facing a 1918-like scenario. ... We would have no surge capacity for health care, food supplies, and many other products and services. ... We have no detailed plans for staffing the temporary hospitals that would have to be set up in high-school gymnasiums and community centers -- and that might need to remain in operation for one to two years. ... We have no way of urgently increasing production of critical items such as antiviral drugs, masks for respiratory protection, or antibiotics for the treatment of secondary bacterial infections. ... Nor do we have detailed plans for handling the massive number of dead bodies that would soon exceed our ability to cope with them."

The WHO expert panel underscores this concern. They note that the H5N1 virus already has resulted in the death -- or culling -- of 100 million chickens and ducks. To date there have been 97 confirmed human cases and 53 deaths in Vietnam, Thailand, and Cambodia. Many more cases undoubtedly have gone unreported.

"H5N1 viruses have the potential to cause far greater harm if they evolve and gain the ability to easily infect and transmit among people," the panel's report notes. "An H5N1 virus with this ability could lead to a global pandemic and many millions of deaths worldwide."