The Sky Is Falling, The Sky Is Falling

(CBS/AP) World Health Organization officials urged governments on Wednesday to act swiftly to control the spread of the bird flu, warning that the world is in grave danger of a deadly pandemic triggered by the virus.

The bird flu has killed 45 people in Asia over the past year, in cases largely traced to contact with sick birds, and experts have warned the H5N1 virus could become far deadlier if it mutates into a form that can be easily transmitted among humans. A global pandemic could kill millions, they say.

"We at WHO believe that the world is now in the gravest possible danger of a pandemic," Dr. Shigeru Omi, the WHO's Western Pacific regional director, said Wednesday.

He said the world is "now overdue" for an influenza pandemic, since mass epidemics have occurred every 20-30 years. It has been nearly 40 years since the last one.

Speaking at the opening of a three-day bird flu conference in Ho Chi Minh City, Omi said it is critical that the international community better coordinate its fight against the virus.

In recent outbreaks, bird flu has become more deadly than the strain found in 1997 in Hong Kong, making the situation more urgent, he said.

The mortality rate among identified patients who contract the disease from chickens and ducks is about 72 percent, says Dr. Julie L. Gerberding, head of the U.S. Centers for Disease Control and Prevention. She adds that her agency was preparing for a possible pandemic next year.

"What we don't know yet," she continues, "is whether or not there (others) with very mild illness who aren't coming to our attention, or even people who aren't actually sick but have been exposed and developed immunity to the virus."

Last year, notes The Early Show medical correspondent Dr. Emily Senay, the bird flu spread to ten countries in Asia, and hundreds of millions of chickens and ducks have been slaughtered in an effort to contain the virus. But, despite the precautions, bird flu continues to infect both birds and humans.

"We have the ideal circumstances for the flu virus to evolve," Gerberding cautions. "If it evolves in a direction that allows it to be more successfully transmitted to humans and then from one human to another, we have the setup for a very serious flu outbreak, or even a pandemic."

So far, Senay points out, the bird flu in Asia doesn't appear to spread easily from person-to-person. But health officials are preparing for the day they may have to face a more dangerous disease.

"There is certainly a statistical probability that this could evolve into something that would pose an imminent threat to people's health," Gerberging says. "There's no evidence of that yet, but we have to stay on top of it, and we can't be complacent. We really do need to be prepared."

In the U.S., Senay notes, the CDC is helping to monitor the spread of the bird flu and to analyze new strains that surface, and researchers are getting a headstart on developing vaccines against strains of bird flu that have already been identified. Two million doses of vaccine that would protect against the known strains of Avian flu have been ordered, and anti-viral medications to treat the flu have been stockpiled.

But, Senay adds, the worst-case scenario would see the the bird flu mutating into a new human strain of influenza that we have no immunity or vaccine for. Such a disease could be very dangerous and spread quickly around the world, causing a pandemic, or global disease. A similar influenza strain in 1918 killed tens of millions of people around the world.