Scientists have discovered a new strain of bird flu that appears to sidestep current vaccines.

It's infecting people as well as poultry in Asia, and some researchers fear its evolution may have been steered by the vaccination programs designed to protect poultry from earlier types of the H5N1 flu.

The discovery by Yi Guan of the University of Hong Kong and colleagues is reported in Tuesday's issue of Proceedings of the National Academy of Sciences.

The new variant has become the primary version of the bird flu in several provinces of China and has spread to Hong Kong, Laos, Malaysia and Thailand, the researchers report. It is being called H5N1 Fujian-like, to distinguish it from earlier Hong Kong and Vietnam variants.

"We don't know what is driving this," report co-author Dr. Robert G. Webster of St. Jude's Children's Research Hospital in Memphis, Tenn., said in a telephone interview.

New vaccines will have to be developed, Webster said.

Many scientists are going to think the vaccination program encouraged the virus to evolve resistance, he added, but high-quality vaccines can reduce the level of illness and prevent emergence of variants.

While the new virus has infected people, there is no evidence that it can pass easily from person to person, Webster said. However, he added, "this virus is continuing to drift."

No sign of increased risk, WHO official says

Dr. Michael L. Perdue, of the World Health Organization's Global Influenza Program in Zurich, Switzerland, said the new variant doesn't indicate any increased risk for people "other than the fact it seems to be pretty widespread." The virus is continuing to change, he added.

Perdue, who was not part of Webster's research team, said WHO is working with the Chinese Ministry of Health to develop a vaccine for the new form of the virus.

The H5N1 flu has devastated poultry in China and several Southeast Asian countries and also has claimed more than 150 human lives. Most of the people affected lived close to flocks of chickens or other poultry.

Public health authorities fear that the virus will mutate into a form that can spread easily among people, raising the potential for a worldwide pandemic like the one that killed millions in 1918.

That worry has spurred efforts to develop vaccines for the virus as well as to test migrating wildfowl in an effort to detect movement of the disease.

Studding the virus's surface are two proteins called hemagglutinin — the H in H5N1 — and neuraminidase, the N. There are 16 known hemagglutinin versions and nine neuraminidases.

They trigger the immune system to mount an attack, particularly hemagglutinin, the protein the body aims for when it makes flu-fighting antibodies.

The research was funded by the Li Ka Shing Foundation, a Hong Kong group that supports medical, educational and cultural work, and the U.S. National Institute of Allergy and Infectious Disease.