Anthrax vaccine makeover

New regimen eases some side effects that have hampered acceptance

Less is better for the much-maligned anthrax vaccine, a new study suggests. People getting a slightly different kind of injection had less pain but no diminished protection against the disease, even when they got fewer shots, researchers report in the Oct. 1 Journal of the American Medical Association.

The study reports on the first seven months of a multiyear test of this new technique and dosing. Researchers expect to assess the full results next year. Meanwhile, the findings might raise hopes that the vaccination regimen, routinely given to military personnel as a defense against biological warfare, will help the vaccine gain more widespread acceptance and lessen the fear of side effects.

An independent advisory panel and federal regulators will make the ultimate decision on whether to change the standard vaccine regimen.

“Will this make it more acceptable?” asks Conrad Quinn, a microbiologist at the Centers for Disease Control and Prevention in Atlanta and coauthor of the new study. “One would anticipate that if you can improve the side-effect profile … that that would encourage a greater level of confidence in the vaccine.”

That confidence level has taken a beating since the current vaccine course was devised in the 1960s. With the increased risk of biological warfare in recent decades, the Department of Defense began to vaccinate personnel. But many complained of nausea, fatigue and other symptoms, and others refused the vaccine — even at the risk of a court-martial. Meanwhile, more recent terror attacks underscored the need for having a protective stock of effective and safe vaccine against an anthrax-based bioterror attack.

The anthrax vaccination regimen currently approved for use requires six shots over 18 months with annual boosters thereafter. It uses subcutaneous injections that enter the skin at an angle and deposit the vaccine in the layers of tissue underneath. The delivery tested in the new study uses an intramuscular shot that is more direct and goes deeper.

Quinn and his colleagues recruited 1,005 military and civilian volunteers and randomly assigned them to get a series of subcutaneous or intramuscular anthrax vaccine shots. A control group received saline injections. Over seven months, volunteers who got three vaccine shots generated an immune response that was just as potent as that made by volunteers getting four. A separate analysis comparing the intramuscular to subcutaneous shots also showed equal potency.

Anthrax vaccination engenders the manufacture of antibodies that neutralize the toxin made by the anthrax bacterium, Bacillus anthracis. Scientists measured antibody levels to verify the vaccine’s effectiveness. The placebo group didn’t generate an antibody response.

Overall arm pain from injections was 50 percent lower in the intramuscular group compared with the subcutaneous group, as measured per shot. Also, people getting only three injections had commensurately less pain and discomfort than those getting four. The participants reported their reactions at clinic visits and in diaries kept during the trial.

Women had significantly more skin irritation and pain at an injection site than men and were more likely to report fatigue, headache and muscle ache after vaccination.

As part of the long-term study, the researchers are halving the 18-month vaccine dosage from six shots to three in some volunteers, Quinn says. If successful, that would double the available vaccine supply.

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