In the largest study ever conducted of an anthrax vaccine, researchers found they could achieve the same level of immune response, with fewer side effects, by giving the vaccine in the muscle rather than under the skin and by giving fewer doses.
The results, which are published in the October 1 issue of JAMA, will help optimize the way in which anthrax vaccine adsorbed (AVA), the only currently licensed anthrax vaccine, is administered. In 1998 the Department of Defense made the vaccine mandatory for all military personnel, affecting 2.4 million people in the United States.
The Centers for Disease Control and Prevention led the study. Emory University was one of five study sites, along with Mayo Clinic, Walter Reed Army Institute of Research, University of Alabama, Birmingham and Baylor College of Medicine.
"It was important to conduct this study to evaluate alternative methods of anthrax vaccine administration to decrease local pain on injection," says Harry Keyserling, MD, professor of pediatrics (infectious diseases) at Emory University School of Medicine and principal investigator of the Emory arm of the study.
The licensed AVA vaccine regimen is administered by injection under the skin (subcutaneously) at 0, 2, and 4 weeks and 6, 12 and 18 months, followed by annual boosters.
In the randomized clinical study, participants received AVA either by subcutaneous or intramuscular injection at 0, 2, and 4 weeks and 6 months, or at a reduced 3-dose schedule. A control group received saline injections at the same time intervals.
The researchers found that after seven months all groups had antibody responses that were as good as the licensed regimen. The group receiving intramuscular injections had fewer adverse events including pain, warmth, tenderness, itching, abnormal redness of the skin, swelling and arm motion limitation. Also, in the intramuscular group, pain immediately after injection was reduced by half. Women benefited even more than men from reduced side effects.
The study is continuing in order to evaluate whether any of the booster injections at 12, 18 and 30 months could be dropped.