New vaccine may beat bird flu before it starts

WASHINGTON (Reuters) - Researchers studying bird flu viruses said on Thursday they may have come up with a way to vaccinate people before 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.

"If we can define what changes need to be made to make that jump then we can target the immune system to that spot on the virus," Nabel said in a telephone interview.

"It gives us a chance to develop vaccines or monoclonal antibodies ... to really work in a preemptive way to be prepared."

Monoclonal antibodies, often used against cancer, are engineered immune system proteins that specifically attack proteins on a tumor or, in this case, on the flu virus.

"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," National Institutes of Health Director Dr. Elias Zerhouni said in a statement.

LEARNING FROM DISASTER

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 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 an antibody that could neutralize both types of H5N1 -- H5N1 adapted to birds, and an engineered form that would in theory prefer humans.

"It delivers a powerful blow against this virus and really hits it where it lives," Nabel said.

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

A monoclonal antibody could be used to treat people who were already infected, he added.

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

Nabel said his team was working on some possible vaccines using the new approach.