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Researchers at St. Louis U. expand anthrax vaccine trial

By Tina Hesman Saey

Researchers at St. Louis University will expand clinical trials for a new anthrax vaccine after promising results from the first phase of testing.

The researchers, led by Dr. Geoffrey J. Gorse at St. Louis University, reported the initial results of clinical trials with the new vaccine in the journal Vaccine.

The first phase of the trial was to test the safety of the vaccine and to see whether it could be effective in fewer doses than the vaccine used by the military.

The military vaccine is made from culture medium in which anthrax grows and might contain toxins and other bacterial proteins that cause side effects. The side effects include pain, swelling and hardening of tissues at the injection site, fever, flulike symptoms, and swelling lymph nodes.
People must get six injections of the military vaccine over 18 months and annual booster shots to induce immunity to anthrax.

"That's cumbersome," Gorse said.

The U.S. government contracted VaxGen Inc. of Brisbane, Calif., to develop an anthrax vaccine for civilian use.

The new vaccine contains a purified protein from the anthrax bacterium called recombinant Protective Antigen.

The researchers tested the new vaccine at four medical centers, including SLU, Baylor College of Medicine in Houston, Emory University in Atlanta and Johns Hopkins University in Baltimore. Volunteers were divided into five groups of 20. One group got two injections of the old vaccine. Each of the other groups got three injections of the new vaccine.

The researchers tested four different doses of the new vaccine. People who got the two highest doses of the new vaccine produced antibodies at a level that could protect against anthrax infection.

Volunteers who got the investigational VaxGen vaccine had a headache after the first injection more often than people who got the old vaccine, Gorse said. The headache wasn't severe and didn't come back after the second or third injection, he said.

The study contained too few volunteers to determine the frequency of other potential side effects, he said.

The researchers are expanding the study to include 400 volunteers in a Phase II clinical trial. The purpose of the new study is to determine how the vaccine should be formulated.