U.S. Not Ready for Fast-Spreading Bird Flu, Study Finds

John Roach
for National Geographic News

April 3, 2006

Scientists have used a sophisticated computer model to predict how a deadly flu virus might spread through the United States, and how the disease might respond to efforts to contain it.

The results suggest that the U.S. is prepared to contain a virus with low transmissibility but perhaps not one that spreads more quickly.

Another team of scientists has also reported that it has developed a preliminary human vaccine against bird flu. But the team acknowledges that more work is needed before the vaccine could successfully contain an outbreak.

Many scientists believe the threat of a bird flu pandemic is real. Researchers are particularly concerned that the virus currently spreading around the world—the highly pathogenic avian flu strain H5N1—might mutate, allowing it to be transmitted between humans.

If such a mutation were to occur, the result could be a global pandemic similar to that of the 1918 "Spanish flu," which killed an estimated 20 to 40 million people worldwide.

"It's still up in the air how readily H5N1 can become human-to-human, but almost certainly there will be another pandemic at some point," said Timothy Germann, a chemical physicist at the Los Alamos National Laboratory in New Mexico.

Germann led the team that developed the computer model.

Christian Sandrock, an infectious-disease expert at the University of California, Davis, said pandemics have historically occurred about every 20 to 30 years.

He said another pandemic is a question of when, not if. The unknown is what the virus will look like. (Read National Geographic magazine's "Tracking the Next Killer Flu.")

"We have no idea what will come out of the gate when it happens," he said.

"Whether it is H5N1 or something totally different is hard to predict."

Computer Model

The computer model developed by Germann's team combines information about influenza transmission with U.S. population and transportation data to study how a virus could spread.

The model assumes a human-transmissible virus will be introduced to the U.S. via international air travel.

The model's findings include these projections:

• Due to the high frequency of domestic travel, the virus could be seeded in communities nearly simultaneously across the country once it arrives in the U.S.

• Given how humans interact in their homes, schools, places of work, shopping malls, and on the occasional long-distance trip, a highly transmissible strain would create a pandemic within 24 days.

• A containment strategy that included travel restrictions, widespread vaccinations, and the development of a vaccine targeted to the specific strain could limit the number of people infected to less than 10 percent of the U.S. population.

• While restrictions such as school and airport closures would not by themselves limit the number of people infected, such measures could buy researchers time to develop a specific vaccine based on the pandemic virus.

Exactly what measures should be taken will depend on the transmissibility of the virus, Germann said. This factor cannot be determined until an outbreak occurs, and even then it is difficult to gauge.

"How [transmissibility] is determined is still somewhat controversial," he said.

In addition, he added, before officials can put a vaccine plan in place, the U.S. needs to stockpile a so-called best-guess vaccine for the most common flu strains, and must develop the capacity to produce targeted vaccines rapidly once an outbreak occurs.

Neither precaution currently exists in the U.S. for a highly transmissible strain, Germann said.

Without any vaccines or interventions such as travel restrictions in place, he said, the U.S. would need 182 million courses of the antiviral drug oseltamivir (sold under the trade name Tamiflu) to combat a virus with the same transmissibility of the virus that caused the 1918 pandemic.

The current national stockpile of Tamiflu stands at about 5 million courses.

The results of the computer-model study appear in this week's issue of the Proceedings of the National Academy of Sciences.

Sandrock, who was not involved in the study, said the model does a "good job" at representing the virus spread and potential containment strategies.

But, he cautioned, "nothing is uniform in life as compared to a mathematical model."

Vaccine Development

A second team reports that there is some promise for the development of a bird flu vaccine.

According to a study in last week's New England Journal of Medicine, scientists have developed an experimental bird flu vaccine for humans that protected about half the people vaccinated.

But the vaccine requires a dose up to 12 times larger than a regular flu shot. At that dosage, the vaccine is too difficult to mass-produce, the team said.

"We have a long way to go," Anthony Fauci, director of the National Institute of Allergy and Infectious Disease (NAID), told reporters in a telephone conference last week, according to news reports.

NAID, a division of the U.S. National Institutes of Health, funded the research.

Lead investigator John Treanor of the University of Rochester in New York and his colleagues are now attempting to stretch the vaccine with an adjuvant, a substance that enhances the response of the immune system.

NAID is also looking at ways to speed the vaccine manufacturing process, as well as new ways to deliver vaccines.

According to Sandrock, the pandemic response system as a whole is not yet ready. But, he said, "We are getting there."

Free Email News Updates
Sign up for our Inside National Geographic newsletter. Every two weeks we'll send you our top stories and pictures (see sample).