The anthrax vaccine is not currently recommended for the general population anywhere in the world. However, because anthrax spores were sent via the mail with criminal intent in the U.S. following Sept. 11, 2001, any presumed incidents related to bioterrorism in the future would almost immediately cause a re-evaluation of the current recommendations. In all likelihood, revised recommendations for receipt of the anthrax vaccine would only target groups considered to be at high risk of exposure based on the situation.

The risk for exposure to anthrax in the United States is low. Currently, the anthrax vaccine is only recommended in the United States for military personnel, lab personnel, and handlers of animals or animal products who are at the highest risk for exposure to 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, and annually or every three years thereafter, depending on risk.

The disease

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 or contaminated animal products. The people most likely to get anthrax are those who work in slaughterhouses. Anthrax is not spread from person to person.

Most cases of anthrax occur when bacteria enter 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 2 percent of infected persons will die.

If people eat infected meat, they may experience fever, chills, swollen glands, sore throat, difficulty breathing, nausea, vomiting, diarrhea, stomach pain, and flushed face or red eyes. Typically, patients will have some, but not all of these symptoms, depending on what part of the digestive tract is most affected.

People can also be infected by inhaling, or breathing in, anthrax spores. When this happens, they can experience difficulty breathing, coughing, chest discomfort, confusion, nausea or vomiting, stomach pain, sweating or dizziness. Even with treatment about 4 or 5 of 10 people will die.

On occasion, people can be infected with anthrax through injection of heroin. When this happens, they may experience swelling at the injection site, nausea, vomiting, and sweating.

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 reported in 1992. In 2001, members of the media and postal workers were infected by anthrax following distribution of letters containing anthrax spores.

The vaccine

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?

At least 95 of 100 people given at least two 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 in the study got anthrax disease after breathing in the anthrax spores — none of the five had 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 ten 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 experience a short period of 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.

Other questions you might have

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 anthrax-vaccinated 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 did not cause GWS.

Do antibiotics treat anthrax?

Antibiotics such as penicillin, doxycycline and ciprofloxacin have all been found to kill anthrax bacteria and can be used effectively in the treatment of patients with anthrax.

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

The problem with antibiotics is that they can kill anthrax bacteria, but they don’t kill anthrax spores. In the event of a bioterrorist attack, spores would be released into the air and inhaled. Antibiotics would prevent the development of anthrax disease, but they would not necessarily kill all of 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 inhaled spores 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.

Why is anthrax considered to be a potential bioterrorist threat?

Anthrax bacteria have been manufactured as an agent of biological warfare. 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, with widespread distribution, inhaled by a large percentage of the population.
• Anthrax spores, more so than spores from other bacteria, are stable for long periods of time in the environment.
• Anthrax spores, when inhaled, are phenomenally deadly — about 95 of 100 people who inhale enough spores, and are not quickly treated 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.

Relative risks and benefits

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 (i.e., occasional pain, redness, and tenderness at the site of injection; rarely, fever, chills, body aches and nausea).

No evidence supports an association between receipt of anthrax vaccine and long-term side effects. Therefore, for military personnel and others at high risk of exposure to anthrax spores, the benefits of the anthrax vaccine outweigh the risks.

Disease risks

• Easily spread via biological warfare
• Antibiotics don't always work
• Disease can be fatal

Vaccine risks

• Pain, redness and swelling at the injection site (1 in 10 people)
• Severe pain and swelling (1 in 100 people)
• Fever, chills, body aches, and nausea (4 in 7,000 people)

Reference

Plotkin SA, Orenstein W, Offit PA, and Edwards K. Anthrax Vaccines in Vaccines, 7th Edition. 2018, 134-148.