Some People May Be Immune to Bird Flu, Mouse Study Suggests

By John Lauerman

Feb. 12 (Bloomberg) -- Some people already may have at least partial protection to the deadly bird flu spreading in Asia, possibly because of getting seasonal flu shots, scientists said today.

The conclusions, published online today by researchers from St. Jude Children's Research Hospital in Memphis, Tennessee, are based on a study of mice that were protected against the deadly virus after gaining immune proteins found in many people.

The findings open a window into how the body gains immunity against influenza, a highly contagious virus that kills about 36,000 Americans annually and causes deadly pandemics a few times each century. It also might give an unexpected boost to the use of seasonal flu shots, made by Sanofi-Aventis SA and other companies, for the strains that spread around the world annually.

``This makes seasonal immunization more important because it might provide some partial protection,'' said William Schaffner, a Vanderbilt University infectious disease specialist in Nashville, Tennessee, who didn't participate in the study. The study may become ``an additional argument to get people to line up and get immunized either by inoculation or nasal spray.''

Countries and companies have stepped up their anti-influenza efforts as a deadly bird flu has spread through Asia, Africa, the Middle East and parts of Europe. Scientists say the disease might kill millions if it becomes contagious in people.

H, N Proteins

Sanofi, GlaxoSmithKline Plc, Novartis AG and other drugmakers design new vaccines annually to find and destroy two constantly changing proteins, called ``H'' and ``N'' for short, on the surface of the flu virus. Vaccine specialists have long considered the more important of these two to be hemagglutinin, the ``H'' protein that attaches the virus to the surface of human cells, Schaffner said.

The St. Jude's research team, led by virologist Richard Webby, focused on immunity to the other surface protein, called ``N,'' or neuraminidase. Similar versions of the neuraminidase, known as ``N1,'' sit on the outside of both H5N1 bird flu and another influenza strain, called H1N1, that has been circulating among people for decades.

Webby's group wanted to see if immunity to the N in H1N1 would also protect against the deadly H5N1 bird flu. About half of animals with genes programmed to give immunity to H1N1's ``N'' protein survived H5N1 infection; every animal in a comparison group died.

``It's very weak protection,'' Webby said, ``but I was surprised we saw any protection at all because of the differences in the neuraminidase proteins.''

Descendants of H1N1

The most deadly pandemic known in history, the 1918 Spanish flu that killed about 50 million people worldwide, was caused by a virus in the H1N1 family.

Since then, descendants of that virus have circulated widely in people, and vaccines against different versions of H1N1 are included in seasonal vaccines. Mice who were given human serum, a blood component that contains immune cells, also gained some protection against H5N1.

Statistics released last week by the World Health Organization showed that 90 percent of people infected with H5N1 since 2003 are less than 40 years old. At least 272 people have been sickened by the virus, and 166 of them have died, WHO said Feb. 6.

The findings, published today in the Public Library of Science, Medicine, may explain why H5N1 bird flu infections have been so rare, particularly in older people, researchers said. Years of exposure to annual outbreaks and vaccines may have given people antibodies that protect against the N1 protein.

``This could be a matter of considerable relief,'' said David Fedson, a former vaccine developer for Aventis Pasteur, a unit of Paris-based drugmaker Sanofi-Aventis SA.

Mice, Ferrets, Humans

Still, results in mice don't always predict what will happen in humans, Fedson and other scientists said. Ferrets are thought to mimic more closely the human response to influenza and vaccines, said Arnold Monto, a University of Michigan School of Public Health epidemiologist.

``The proof of the pudding is going to be in whether this can be replicated in other testing systems,'' he said in a telephone interview. ``We need to see if it works in other animals like ferrets.''

The real answer won't be known until when and if H5N1 begins spreading in people, Fedson said.

``To think that we know from lab tests all we need to know about this virus would be risky,'' he said.

To contact the reporter on this story: John Lauerman in Boston at .


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