The anthrax vaccine can also be used, along with medication, after an exposure. In this case, three doses are given under the skin. The second and third doses are given two and four weeks after the first dose. But the schedule could change depending on the situation, such as if there was a mass casualty event and vaccine was in short supply. Hopefully, we will never find ourselves in this situation.

The disease

What is anthrax and how do you catch it?

Anthrax is caused by the bacterium, Bacillus anthracis. The spores of this bacterium live in the soil and are consumed when animals (such as cattle, sheep, goats, camels and antelopes) eat grass. 

People get anthrax when they come in contact with infected animals or contaminated animal products. Those most likely to get anthrax work in slaughterhouses. Anthrax is not spread from person to person.

Symptoms depend on how people were exposed to the bacteria. People can be exposed in three main ways:

• Direct contact — Most cases of anthrax occur when bacteria enter the skin through a cut or wound while the person is handling contaminated meat, wool, hides, leather or hair products from infected animals. Symptoms typically appear about two to seven days after exposure. The first symptom is often a small red area on the skin that progresses to a blackened, painless ulcer. Soon, the person’s lymph glands begin to swell, and they may have a fever, tiredness and a headache. About 1 of 5 people will have trouble breathing and develop a bloodstream infection that causes death. If the person receives antibiotic treatment, they are much less likely to die. Only about 2 of 100 people die if they get timely treatment. This is called cutaneous anthrax.
• Eating contaminated meat — People who eat contaminated meat can have fever, chills, swollen glands, sore throat, difficulty breathing, nausea, vomiting, diarrhea, stomach pain, and flushed face or red eyes. Symptoms usually begin two and seven days after exposure. Typically, people will have some of the symptoms listed here, depending on what part of their intestine is affected. This is called gastrointestinal anthrax.
• Breathing in the bacterial spores — People infected by inhaling the spores can have trouble breathing as well as have coughing, chest discomfort, confusion, nausea or vomiting, stomach pain, sweating or dizziness. Even with treatment about 4 or 5 of 10 people infected by this route will die. This is why anthrax is considered as a potential bioweapon that could result in a mass casualty event. The U.S. has prepared for this possibility by developing response plans and stockpiling medication and vaccines in the event of such an attack. This is called pulmonary anthrax.

A fourth and quite rare way of getting anthrax is through injection of heroin. This is called injection anthrax. It is thought that anthrax spores may be introduced if the drug is wrapped in animal skins during transport or if animal products, such as bone meal, are added during preparation. However, because cases are rare, the exact source is uncertain. A person infected in this way may experience swelling at the injection site, nausea, vomiting, and sweating. They may also develop severe lesions of the skin and soft tissues at or near the injection site.

Anthrax is rare in the U.S. At the beginning of the 20th century, it was estimated that about 130 cases of anthrax occurred every year. Now, because of improved testing and handling of animals and vaccination of livestock, anthrax has virtually disappeared. Cases in people do occur sporadically, often in or near an area of the U.S. referred to as the “Anthrax Triangle.” This area includes eight counties in Texas. Here, as well as in parts of Colorado, North Dakota, South Dakota and Montana, the acidity of the soil provides a good environment for survival of anthrax spores. As animals graze on the land, some get infected with the bacteria, and on occasion, the spores spread to people handling the animals. About 10 cases occurred in people in the U.S. between 2006 and 2025.

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. As the bacteria reproduce, they release several harmful proteins, called toxins, into the surrounding broth. These toxins are responsible for disease. The toxins are collected and inactivated with formaldehyde, which makes them harmless. The anthrax bacteria are filtered out of the vaccine. 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 many studies on the effectiveness of the anthrax vaccine. However, 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. About 92% of the people who got the vaccine developed antibodies. More importantly, a chance occurrence provided further evidence that the vaccine worked. During the study, an outbreak of inhalational anthrax occurred. Inhalational anthrax would be likely if anthrax were used as a biological weapon by releasing a large quantity of spores into the air. Five people in the study got anthrax disease after breathing in the anthrax spores — none of the five had received the vaccine. This was important for understanding how the vaccine would work should a bioterrorist situation occur.

Does the anthrax vaccine have side effects?

People who get the anthrax vaccine can have some side effects:

• Mild pain, redness and swelling at the injection site (1 of 10 people)
• Severe pain and swelling at the injection site (1 of 100 people)
• Short period of fever, chills, body aches or nausea (4 of 7,000 people)
• Severe allergic reaction (called anaphylaxis) that includes difficulty breathing, hives or lowered blood pressure (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. It was called Gulf War syndrome (GWS). Some people suggested that GWS was caused by the anthrax vaccine. A study was performed to check whether that claim was true. Blood was taken from anthrax-vaccinated people who complained of symptoms of GWS and from those who did not. Both groups had similar numbers of people with antibodies against anthrax, suggesting that the anthrax vaccine did not cause GWS. 

Do antibiotics treat anthrax?

Yes. Some antibiotics, such as penicillin, doxycycline and ciprofloxacin, have been found to kill anthrax bacteria and are used to treat patients with anthrax.

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

The vaccine is of value for a couple of reasons.

First, antibiotics 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 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.

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

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, they could be inhaled by a large percentage of the population in a relatively short period of time.
• Anthrax spores, more so than spores from other bacteria, are stable for long periods of time in the environment.
• When anthrax spores are inhaled, they are quite deadly — about 95 of 100 people who inhale enough spores will die if they are not immediately treated with antibiotics. While development of symptoms usually takes a couple of days to a week, if a person inhales enough spores, the time from exposure to symptoms 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 the U.S. The U.S. military is particularly at risk of such an attack. Anthrax is a frightening agent in biological warfare because it is easily sprayed over a large area. Once inhaled, if untreated with antibiotics, anthrax spores can often cause a 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 for people considered to be at high risk. 

On the other hand, the anthrax vaccine has side effects similar to vaccines routinely recommended for children, such as the pertussis or whooping cough vaccine. Also, studies don’t support an association between anthrax vaccine and long-term side effects, such as Gulf War syndrome. 

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

Orenstein W, Offit PA, Edwards K, and Plotkin SA. Anthrax Vaccines in Vaccines, 8th Edition. 2024, 157-171.

Reviewed by Paul A. Offit, MD, on October 24, 2025