By Maggie Fox, Health and Science Editor

WASHINGTON, Aug 9 (Reuters) - Researchers studying bird flu viruses said on Thursday they may have come up with a way to vaccinate people ahead of a feared influenza pandemic.

Experts have long said there is no way to vaccinate people against a new strain of influenza until that strain evolves. That could mean months or even years of disease and death before a vaccination campaign began.

But a team at the National Institute of Allergy and Infectious Diseases in Maryland and the Emory University School of Medicine in Atlanta said they may have found a short-cut.

The vaccine might protect people against the mutation that would change the H5N1 avian flu virus from a germ affecting mostly birds to one that infects people easily, the NIAID's Dr. Gary Nabel and colleagues report in Friday's issue of the journal Science.

"What Dr. Nabel and his colleagues have discovered will help to prepare for a future threat," NIH Director Dr. Elias Zerhouni said in a statement.

"While nobody knows if and when H5N1 will jump from birds to humans, they have come up with a way to anticipate how that jump might occur and ways to respond to it."

H5N1 remains mainly a virus of birds, but experts fear it could mutate into a form easily transmitted from person to person and sweep the world. It has occasionally infected people, killing 192 people out of 319 known cases since 2003, according to the World Health Organization.

To better try and understand the threat, researchers have studied various strains of H5N1 and compared them to the worst known flu virus ever -- the H1N1 virus that killed anywhere between 50 million and 100 million people in 1918 and 1919.

They found a tiny mutation that makes one strain of the H1N1 virus more easily infect birds, and another one prefer humans. It lies in the part of the virus that attaches to cells in the respiratory tract.

They then made the same alteration in an H5N1 virus, and vaccinated mice with some of this genetically engineered H5N1 DNA.

They found one immune system protein called an antibody that could neutralize both types of H5N1 -- H5N1 adapted to birds, and an engineered form that would in thery prefer humans.

If a vaccine could be designed to protect people against viruses with this mutation, it might be used to vaccinate populations before a pandemic even started, the researchers said.

"Now we can begin, preemptively, to consider the design of potential new vaccines and therapeutic antibodies to treat people who may some day be infected with future emerging avian influenza virus mutants," NIAID director Dr. Anthony Fauci said in a statement. "This research could possibly help to contain a pandemic early on."

Companies are already making human vaccines against H5N1, but they are designed using the current strain of the virus, which does not easily infect people. Scientists fear they are a poor match for any form of the virus that may eventually infect people.

AlertNet news is provided by