Vaccine Education Center

A Look at Each Vaccine: Anthrax Vaccine

The anthrax vaccine is recommended for military personnel likely to be exposed to anthrax spores during a bioterrorist attack. The vaccine was also recommended for postal workers who served areas that were the target of letters that contained anthrax spores. The vaccine is given as a series of five shots. After the first shot, the vaccine is given four weeks, six months, 12 months, and 18 months later.

What is anthrax and how do you catch it?

The disease, anthrax, is caused by the bacterium, Bacillus anthracis. The spores of this bacterium live in the soil and are eaten by grazing livestock (such as cattle, sheep, goats, camels, antelopes and other herbivores). People get anthrax when they come in contact with infected animals. The most likely people to get anthrax are those who work in slaughterhouses.

Most cases of anthrax occur when the bacteria enters the skin through a cut or abrasion in people who are handling contaminated meat, wool, hides, leather or hair products from infected animals. About seven days after exposure, symptoms of anthrax begin. The disease begins as a small red area on the skin and progresses to a blackened, painless ulcer. Soon lymph glands begin to swell and the patient may have fever, fatigue and headache. About 20 percent of those infected will develop difficulty breathing and a bloodstream infection that causes death. If treated with antibiotics, less than 1 percent of infected persons will die.

Anthrax is very rare in the United States. At the beginning of the 20th century it was estimated that about 130 cases of anthrax occurred every year. But now, with improved conditions for the testing and handling of animals, anthrax has virtually disappeared. The last case of natural anthrax in the United States was in 1992. In 2001, members of the media and postal workers were infected by anthrax following distribution of letters containing anthrax spores.

Why should military personnel be vaccinated?

Anthrax bacteria have been manufactured as an agent of biological warfare and members of the military would be at greatest risk during a bioterrorist attack.

Anthrax is considered one of the most dangerous and lethal agents for a bioterrorist attack for several reasons. Anthrax spores can be easily sprayed into the air, and, because everyone breathes, taken up by a large percentage of the population. Also anthrax spores, more so than spores from other bacteria, are very stable for long periods of time in the environment. Finally, anthrax spores, when inhaled, are phenomenally deadly — about 95 percent of people who inhale enough spores, and are not treated quickly with antibiotics, will die. Although not typical, the time from exposure to anthrax spores to symptoms of anthrax disease can be as short as one day!

How is the anthrax vaccine made?

The anthrax vaccine is made by taking a strain of the bacterium, Bacillus anthracis, and growing it in the laboratory. The bacteria release several harmful proteins, called toxins, into the surrounding broth. These toxins are responsible for disease in those infected with the anthrax bacteria. The toxins are then inactivated with formaldehyde so that they can no longer cause disease. The anthrax bacteria are filtered out of the vaccine. Therefore, the anthrax vaccine is made in a manner similar to the "acellular" pertussis vaccine.

Does the anthrax vaccine work?

More than 95 percent of people given three doses of the anthrax vaccine will develop high levels of antibodies against anthrax in their blood. Unfortunately, there are not a lot of studies on the effectiveness of the anthrax vaccine, but one study, published in 1962, was interesting. In this study, mill workers at high risk of getting anthrax were given either vaccine or no vaccine. The effectiveness of the vaccine was about 92 percent. What was of interest in this study was that, during the study, an outbreak of "inhalational" anthrax occurred. "Inhalational" anthrax occurs when large numbers of anthrax spores are released in the air and is exactly analogous to what would happen if anthrax were used as a biological weapon. Five people got anthrax disease after breathing in the anthrax spores — all five people had not received the vaccine.

Therefore, the anthrax vaccine appears to be effective in preventing "inhalational" anthrax (the type of anthrax expected in a bioterrorist attack).

Does the anthrax vaccine have side effects?

About one of every five people who receive the anthrax vaccine will develop mild pain, redness, and swelling at the site where the vaccine was given. And about one out of every 100 given the vaccine will develop severe pain and swelling.

In addition, four of every 7,000 people who get the anthrax vaccine will have fever, chills, body aches or nausea after receiving the vaccine. A severe allergic reaction (called anaphylaxis) that includes difficulty breathing, hives or lowered blood pressure is extremely rare.

Does the anthrax vaccine cause Gulf-War Syndrome?

A long-lasting disease that included muscle pain, fatigue and headaches was significantly associated with deployment of military personnel to the Gulf War. Some suggested that Gulf War Syndrome (GWS) was caused by the anthrax vaccine. To determine whether anthrax vaccine caused GWS, a study was performed. Blood was taken from people who complained of symptoms of GWS and from those who did not. The percentage of people who had antibodies to anthrax was not different between the two groups. Therefore, the anthrax vaccine does not appear to be the cause of GWS.

Do antibiotics treat anthrax?

Antibiotics such as penicillin, doxycycline and ciprofloxacin all have been found to kill the anthrax bacteria and can effectively treat patients with anthrax.

If antibiotics treat anthrax, why do military personnel need a vaccine?

The problem with antibiotics is that they can kill the anthrax bacteria, but they can't kill the anthrax spores. If there were a bioterrorist attack, spores would be released into the air and inhaled. Antibiotics would prevent the development of the disease, anthrax, but would not necessarily kill all the spores. If someone took antibiotics for several weeks, or even several months, and then stopped the antibiotics, the spores could reawaken (i.e., germinate) and cause disease. It is unclear exactly how long one should treat with antibiotics before it is certain that all the spores inhaled will not germinate.

Also, not all people with anthrax who are treated with antibiotics survive. As with all diseases in medicine, prevention is always better than treatment.

For these reasons, the vaccine is of value.

Do the benefits of the anthrax vaccine outweigh the risks?

Anthrax bacteria could be used in an attack against military personnel in the United States during a conflict. Anthrax is a frightening agent in biological warfare because it is easily sprayed over a large area. Once inhaled, and if untreated with antibiotics, the anthrax spores can cause a uniformly fatal infection. Because not all people with anthrax who are treated with antibiotics survive, and because the length of treatment for someone who has inhaled spores is unclear, the anthrax vaccine is of value. On the other hand, the anthrax vaccine has a side effect profile similar to vaccines routinely recommended for children. No evidence supports an association between the receipt of the anthrax vaccine and long-term side effects. Therefore, for military personnel, the benefits of the anthrax vaccine outweigh the risks.

Reviewed by: Paul A. Offit, MD
Date: June 2010