Fewer doses of anthrax vaccine comparable to current dosing regimen

HOUSTON -- (September 30, 2008) -- Three injections of anthrax vaccine given into the muscle stimulate comparable antibody responses and cause fewer adverse reactions than four doses given under the skin, said a consortium of researchers that included those from Baylor College of Medicine in a report in the current Journal of the American Medical Association.

"We expect that reducing the number of adverse reactions will lead to a higher level of acceptability of the vaccine," said Dr. Wendy Keitel, professor of molecular virology and microbiology at BCM and director of the Vaccine Treatment and Evaluation Unit at BCM. "And reducing the number of times the vaccine is given will reduce the cost and complexity of delivering the entire program."

Eliminating second dose

Anthrax vaccine is primarily given to people who are at risk for repeated exposure to anthrax spores, such as military personnel deployed to areas where they face an increased risk of infection with the bacteria and people who work with the organism in the laboratory. Eliminating the second dose of the currently recommended schedule would make it easier to fully vaccinate someone, said Keitel.

Researchers studied the ability of a reduced dose schedule to stimulate immune responses and reactions at the vaccine injection site in 1,005 healthy adults between the ages of 18 and 61 years who had not previously received the anthrax vaccine. Study participants were placed at random into one of six groups. Some groups received four scheduled doses at weeks 0, two and four weeks and six months; some groups received placebo as the second dose at two weeks; and some received only placebo injections.

Muscle vs. under the skin

Researchers evaluated antibody responses to the vaccine in the study participants seven months after they received the first dose and found that giving fewer injections into the muscle was comparable to the usual schedule of four given under the skin. They also noted fewer and milder side effects in those who received injections into the muscle rather than under the skin.

Other BCM researchers contributing to the study are Dr. Hanaa El Sahly, assistant professor of molecular virology and microbiology, Nanette Bond, P.A.C., study coordinator, and staff from the Vaccine Research Center. Contributing institutions include University of Alabama at Birmingham, Walter Reed Army Institute for Research, Mayo Clinic, and Emory University School of Medicine.

The study was funded and sponsored by the Centers for Disease Control and Prevention. The CDC was responsible for the development, study protocol and for statistical analyses.

The study can be found at www.jama.ama-assn.org/.