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Inhaled anthrax vaccine promising in early studies

By Anthony J. Brown, MD

NEW YORK (Reuters Health) - An experimental anthrax vaccine that is administered intranasally, rather than by intramuscular injection, can protect against exposure to lethal amounts of Bacillus anthracis, the bacteria that causes anthrax, the results of an animal study show.

The anthrax vaccine currently in use, which was developed over 30 years ago, requires multiple injections and is associated with various side effects. This limits the usefulness of this vaccine in response to emergencies, such as a biological attack with the microbe, researchers point out in the journal Infection and Immunity.

Dr. James R. Baker, from the University of Michigan in Ann Arbor, and colleagues describe the development and testing of a new intranasally administered anthrax vaccine in mice and guinea pigs.

The vaccine consists of a B. anthracis protein that triggers immune protection. This is mixed in a nontoxic water-in-oil nanoemulsion that serves as an "adjuvant," an agent that improves the effectiveness of a vaccine or treatment. This adjuvant enhances penetration of the mucus membranes in the nasal passages to deliver more of the active portion of the vaccine, and avoids the inflammatory side effects seen with the older vaccine.

The researchers found that the experimental vaccine induced bronchial and blood antibodies against B. anthracis in mice and guinea pigs. Further analysis indicated high blood levels of neutralizing antibodies against the anthrax toxin.

The vaccinated guinea pigs were protected against B. anthracis exposure, while all of the unvaccinated animals died within 96 hours of exposure, the report indicates.

The immunity provided by the vaccine appeared to be long lasting as well. In comments to Reuters Health, Baker noted that the "animals were protected for 6 months after second administration" of the vaccine.

He added that "studies need to be performed in humans to confirm the findings" and that these "should begin within a year."

The fatality rates of anthrax are based on the route of transmission, which may be through an opening on the skin, such as a cut (cutaneous); through ingestion, if the bacteria contaminate food; or by inhalation.

Anthrax fatality rates also vary depending on whether the patient receives treatment, which may be successful if started early; but most patients aren't diagnosed until the infection is more advanced.

The mortality rates for untreated and treated infections range from 1 percent to 20 percent for cutaneous transmission and 25 percent to 60 percent for gastrointestinal transmission, respectively. However, the fatality rate for inhalation anthrax is very high -- 75 percent -- with or without treatment.

Symptoms include flu-like symptoms, fever, cough, sore throat, and a sore on the skin that starts as a bump and develops into a painless ulcer with a black area in the center.

SOURCE: Infection and Immunity, August 2007.