A DNA vaccine designed to stop the spread of the H5N1 virus -- known as avian flu -- is being tested in people, the National Institutes of Health said in a news release.

Unlike many vaccines, which inject a weakened form of a virus, this treatment does not contain any infectious material. Just a part of the DNA of the virus is used to get the body to produce antibodies to the potential invader.

Dr. Gary Nabel, who is directing the study, has shown that the technique has promise against other viruses such as HIV, ebola, SARS and West Nile.

The NIH said that 261 cases of avian flu have been confirmed in people. Half of them died.

While the virus is highly fatal and easily transmittable in birds, it has not shown much ability to move person-to-person.