Vaccine protects mice against deadly 1918 virus

WASHINGTON, Oct 18 (Reuters) Researchers trying to find quicker and better ways to make flu vaccines said they had formulated a vaccine that protected mice against the deadliest influenza virus known -- the one that caused the 1918 pandemic.

Their research also helped them find ways to predict how well a vaccine protects against a particular flu strain -- a key step in making vaccines against diseases that are not yet widely circulating.

''Understanding why this influenza virus was so deadly is an extremely important question,'' said Dr. Anthony Fauci, head of the U.S. National Institute of Allergy and Infectious Diseases (NIAID) yesterday, which conducted the study.

''This knowledge will help further our continued efforts to develop treatments and vaccines to protect us against another deadly flu pandemic.'' The 1918 flu killed anywhere between 40 million and 100 million people, depending on the estimate. Researchers have resurrected the virus by digging up the frozen graves of victims and using preserved tissue samples.

On average, influenza pandemics hit three times a century and vary in their severity. The last one was in 1968 and killed about a million people, and experts believe the world is overdue for another.

A likely risk is from H5N1 avian influenza, which has spread around much of the world, killing or forcing the slaughter of more than 200 million birds. It rarely infects humans but has been verified in 256 people and has killed 151 of them in nine countries.

Researchers use the 1918 flu as an example to see how difficult it would be for an avian virus to mutate into a form that easily infects and passes from human to human.

Writing in the Proceedings of the National Academy of Sciences, Dr. Gary Nabel of NIAID and colleagues described how they made a DNA vaccine against the 1918 virus and tested it in mice.

PAST PANDEMICS PREDICT FUTURE ''What we learn about the H1N1 virus that caused the 1918 pandemic is pertinent to other pandemic viruses and to the development of effective and universal vaccines,'' Nabel said in a statement.

Nabel, Terrence Tumpey of the U.S. Centers for Disease Control and Prevention and colleagues immunized the mice and then infected them with their reconstructed 1918 virus.

All 10 vaccinated mice survived, they reported.

They also found that transferring antibody-rich immunoglobulin -- a blood product -- from immunized mice to non-immunized mice helped protect the unvaccinated mice against the virus, too.

Eight of 10 mice given antibodies from the immunized mice survived infection with the 1918 virus while none of the 10 untreated mice did.

''By using an existing pandemic flu strain, this research will provide the basis for design of alternative vaccines against influenza viruses with enhanced virulence,'' Tumpey said.

Government and corporate labs are rushing to make vaccines against H5N1 and other avian influenzas. But flu vaccines must closely match the strain that is circulating and no one knows what the next pandemic flu strain might look like.

Last week, U.S. researchers reported that people immunized with a vaccine based on a 1997 strain of H5N1 were twice as likely to have a strong immune response to a later vaccine than those never immunized before.

That suggested that giving two doses of vaccine, even over a period of years, might protect people better and that it might be possible to start vaccinating people before a pandemic strain of flu even emerges.

Reuters DKA DB0921