Questions & Answers
Anthrax - The Anthrax Vaccine
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Anthrax Vaccine-Effectiveness

  1. Why do we think the anthrax vaccine will protect people if anthrax inhalation occurs? What scientific evidence do we have?
    This vaccine prevents anthrax regardless of route of exposure. Based on human and animal data, the National Academy of Sciences’ Institute of Medicine concluded in March 2002 that anthrax vaccine is “an effective vaccine for the protection of humans against anthrax, including inhalational anthrax, caused by all known or plausible engineered strains of Bacillus anthracis.” The original Brachman and CDC studies of anthrax vaccine in textile workers proved that the vaccine protected against anthrax. The calculations performed in that study combined the cutaneous (skin) and inhalational forms of anthrax infection that occurred. No inhalational anthrax occurred among the vaccinated workers, while five cases of inhalational anthrax occurred among workers who had not been vaccinated. The total number of inhalation cases was judged too few to show statistically conclusive proof of protection by itself. However, results from several animal studies provide additional evidence that the vaccine protects against anthrax challenge with hundreds of times the lethal dose of anthrax by inhalation. This information coupled with the encouraging results of the effectiveness and immune response in humans assures us that the vaccine will greatly increase the chances of soldiers surviving exposure to inhalational anthrax. When full immunization is combined with proper use of protective masks, detection devices, surveillance and post-exposure treatment with antibiotics, the threat is even further reduced.

  2. I heard that the vaccine used in the 1962 Brachman study isn't the same as the vaccine used today. Is that true?
    Yes, it is true that the current vaccine has more protective antigen (PA) in it than Brachman's vaccine formula, and also that the current vaccine is more highly purified than the vaccine used in the Brachman study. Between the time of the Brachman study and the licensing of the vaccine produced in Lansing, the conditions under which the anthrax bacteria were cultured were changed. These changes resulted in a purer, more potent vaccine. Government authorities were aware of and approved the changes at that time the license application was considered in 1970. The independent, civilian review panel advising the FDA was aware of the changes, and described them in its 1985 report. Both vaccine formulas are based on protective antigen (PA), the key protein common to all strains of anthrax.

  3. What will happen if personnel are exposed to anthrax before they gain immunity through vaccination?
    Personnel will be treated with antibiotics if there is a known exposure to anthrax before gaining immunity through vaccination. Antibiotics are effective in treating animals, including primates, exposed to inhalational anthrax, but only if started before symptoms develop. This would usually mean starting antibiotics in the first 24 hours after exposure. Unfortunately, servicemembers may not know they have been exposed until symptoms develop; by then, the infection is nearly always fatal within a few days, whether antibiotics are given or not. The best protection to counter inhalational anthrax is the use of the anthrax vaccine combined with the appropriate Mission Oriented Protective Posture (MOPP), including protective clothing and detection equipment.

  4. If you receive all the shots, are you 100% protected?
    No medication, no vaccine is 100% effecticve. The antibodies that result from any vaccine theoretically could be overwhelmed if one is exposed to extremely large doses of any pathogen. Even if vaccinated, one may not be completely safe if one is close to the point of release of the biologic agent. Antibiotics for such people will offer additional protection. That's why vaccination is only one part of force health protection efforts, which also includes protective gear and detection equipment. For continued protection, annual booster doses are required.

  5. Does anthrax vaccine protect against disease if someone inhales anthrax spores?
    The original studies of anthrax vaccine showed 93% fewer anthrax infections (combining both cutaneous and inhalational cases of anthrax) among vaccinated people, compared to unvaccinated people. In those original studies, no cases of inhaled (inhalation) anthrax occurred among vaccine recipients, while five cases of anthrax occurred among unvaccinated or incompletely vaccinated people. This difference involved too few people to be statistically conclusive, although the trend is obvious. It is unethical to intentionally expose human beings to inhaled anthrax to test the vaccine. Instead, anthrax vaccine was tested on rhesus monkeys. After 65 animals received one or two doses of vaccine, 95% survived aerosol challenge in full health. One animal died from anthrax exposure two years after the second dose of vaccine. This illustrates the importance of annual booster doses of anthrax vaccine. These data lead us to expect that anthrax vaccine would be quite effective in preventing inhaled anthrax.

  6. How long does it take after the first shot before protection begins?
    Antibodies begin to develop within a week or two after the first dose of vaccine. Protection levels increase as shots in the series are given, like walking up a set of stairs. The entire sixshot series is needed for full protection as licensed by the Food & Drug Administration.

  7. Will this anthrax vaccine protect soldiers from all forms of anthrax, including the ones reportedly developed in Russia?
    Every disease-causing strain of Bacillus anthracis causes anthrax disease via the same protein. The vaccine produces antibodies that neutralize that protein. The National Academy of Sciences’ Institute of Medicine concluded in March 2002 that “it is unlikely that either naturally occurring or anthrax strains with bioengineered protective antigen could both evade AVA [the U.S. anthrax vaccine] and cause the toxicity associated with anthrax.” DoD is aware of the Russian research effort recently reported in a British scientific journal. Russian scientists reported using technology to introduce two foreign genes into anthrax. The potential for a genetically altered virulent organism is of concern to us and we are anxious to learn more about this organism. Hamsters, vaccinated with the Russian live attenuated anthrax vaccine were not resistant to challenge with their engineered strain. There are substantive scientific questions about this report. First, the validity of the animal model that the Russians used needs to be addressed, because hamsters may not be predictive of results in other animals (including humans). Second, the strain produced may not be stable, a fact the Russians admit. An unstable organism would not be a candidate for weaponization. There have been ongoing efforts by OSD Cooperative Threat Reduction Program, the National Academy of Sciences, and the International Science and Technology Center to evaluate the possibility of a potential threat from genetically modified strains, and to ensure that our vaccine is effective against them. We believe that the current anthrax vaccine would be effective against altered genetic strains based on the biologic principles of the U.S. vaccine, which is different from the Russian vaccine.

  8. Is the anthrax vaccine licensed for use against biological agents?
    The anthrax vaccine is licensed for people at risk for exposure to anthrax spores. Biological weapons are designed to deliver aerosolized anthrax spores that will result in inhalational anthrax. The FDA concurs that the use of the anthrax vaccine to protect against inhalational anthrax is consistent with indications for use of the vaccine.

  9. For More Information:

    Brachman PS, Friedlander AM, Grabenstein JD. Anthrax. In: Plotkin SA, Orenstein WA, Vaccines, 4th ed. Philadelphia: W. B. Saunders, 2003.

    Brachman PS, Gold H, Plotkin SA, Fekety FR, Werrin M, Ingraham NR. Field evaluation of a human anthrax vaccine. American Journal of Public Health 1962;52:432-45.

    Advisory Committee on Immunization Practices. Use of anthrax vaccine in the United States. MMWR-Morbidity & Mortality Weekly Report 2000;49(RR-15):1-20.

    Food & Drug Administration. Biological products; Bacterial vaccines and toxoids; Implementation of efficacy review. Federal Register 1985;50:51002-117.

    Franz DR, Jahrling PB, Friedlander AM, McClain DJ, Hoover DL, Bryne WR, Pavlin JA, Christopher GW, Eitzen EM Jr. Clinical recognition and management of patients exposed to biological warfare agents. Journal of the American Medical Association 1997;278(Aug 6):399-411.

    Hambleton P, Carman JA, Melling J. Anthrax: The disease in relation to vaccines. Vaccine 1984;2:125-32.

    Inglesby TV, O'Toole T, Henderson DA, Bartlett JG, Ascher MS, Eitzen E, Friedlander AM, Gerberding J, Hauer J, Hughes J, McDade J, Osterholm MT, , Parker G, Perl TM, Russell PK, Tonat K, Working Group on Civilian Biodefense. Anthrax as a biological weapon, 2002: Updated Recommendations for Management. Journal of the American Medical Association 2002;287:2236- 52.

    Ivins BE, Fellows PF, Pitt MLM, Estep JE, Welkos SL, Worsham PL, Friedlander AM. Efficacy of a standard human anthrax vaccine against Bacillus anthracis aerosol spore challenge in rhesus monkeys. Salisbury Medical Bulletin 1996;87(Suppl): 125-6.

    Ivins BE, Pitt MLM, Fellows PF, Farchaus JW, Benner GE, Waag DM, Little SF, Anderson GW Jr., Gibbs PH, Friedlander AM. Comparative efficacy of experimental anthrax vaccine candidates against inhalation anthrax in rhesus macaques. Vaccine 1998;16:1141-8.

    Pitt MLM, Ivins BE, Estep JE, et al. Comparison of the efficacy of purified protective antigen and MDPH to protect non-human primates from inhalation anthrax. Salisbury Medical Bulletin. 1996;87:130.

    Sidell FR, Takafuji ET, Franz DR. Medical Aspects of Chemical & Biological Warfare. Washington, DC: Department of the Army, 1997.

    Turnbull PCB. Guidelines for the Surveillance and Control of Anthrax in Humans and Animals, 3rd ed., WHO Report WHO/EMC/ZDI/98.6.

  10. What is FDA's position about the effectiveness of anthrax vaccine?
    For years, FDA has held that anthrax vaccine prevents anthrax infection regardless of the route of exposure. On December 15, 2005, the Food and Drug Administration released a Final Rule and Final Order for anthrax vaccine. After reviewing extensive scientific evidence and carefully considering comments from the public, the FDA determined that anthrax vaccine is safe and effective in preventing anthrax disease regardless of route of exposure, including inhalation anthrax.