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Prevention
By Mayo Clinic staff
Smallpox vaccine
In 1967, the World Health Organization (WHO) launched a global immunization campaign to eradicate smallpox. The WHO's efforts were remarkably effective, and the last naturally occurring case of smallpox was reported in 1977. In 1980, smallpox vaccinations were discontinued worldwide.
The vaccine today
The United States currently has enough smallpox vaccine to vaccinate all Americans. The CDC has provided public health officials with a contingency plan to quickly inoculate every American should the need arise.
Such a decision would not be undertaken lightly because the smallpox vaccine also has the small but real potential to cause serious harm. Unlike many other vaccines, the smallpox vaccine contains a live vaccina virus — a pox-type virus related to smallpox, but milder than smallpox. The vaccine can't cause smallpox, but because it's live, care must be taken of the vaccination site to keep the virus from spreading. Touching the vaccination site before it's healed, or touching bandages or clothing contaminated with the virus, can cause it to spread to other parts of your body or to other people.
Experts in virology say the vaccine causes a fatal complication in about 1 of every 1 million people who receive it. That means that if the entire American population were to be vaccinated, 300 people would be expected to die of complications from the vaccine. Many others who are vaccinated might develop painful sores and severe scars, and others would likely have residual brain damage from encephalitis — a potentially fatal brain inflammation.
Who should not receive the vaccination
Because of the risk of severe and sometimes fatal reactions, the CDC and WHO recommend that the general public not be vaccinated. But because military personnel and some health care workers continue to be vaccinated, it's important to know who should not receive the vaccine.
You should not receive the smallpox vaccine if you:
- Have certain skin conditions. This includes eczema, a history of eczema or other chronic skin conditions, or sharing a household with someone with eczema, a history of eczema or skin conditions such as impetigo.
- Are pregnant. The vaccine is not known to cause birth defects, but in rare cases it may cause infection of the fetus, leading to stillbirth or death soon after delivery.
- Have impaired immunity. You shouldn't have a vaccination if you have a disease or are undergoing treatment that suppresses your immune system. This includes people with cancer, people with organ transplants, and those undergoing radiation therapy or treatment with drugs that suppress the immune system.
- Have AIDS or are HIV-positive. The human immunodeficiency virus (HIV) wasn't identified before the end of routine smallpox vaccination, so it's not known what effect the vaccine might have on people with the disease. Currently, the CDC recommends that HIV-positive people not be vaccinated.
- Are allergic to any of the ingredients in the vaccine. This includes the antibiotics polymyxin B sulfate, streptomycin sulfate, chlortetracycline hydrochloride and neomycin sulfate.
- Have underlying heart disease. You also shouldn't be vaccinated if you have three or more known risk factors for heart disease, including high blood pressure, diabetes, high cholesterol and smoking, or a parent or sibling of someone with heart disease.
If you were vaccinated before 1972
Many people may have never been vaccinated against smallpox. Others received the vaccine more than 25 years ago. It's not known how long immunity lasts, although it's likely the vaccine is most effective for about three to five years, with immunity decreasing after that. Partial immunity may last much longer. People who are revaccinated appear to have increased immunity, although one recent study indicates that recent or multiple vaccinations aren't essential for maintaining antibodies that protect against the disease.
- Smallpox. Centers for Disease Control and Prevention. http://www.bt.cdc.gov/agent/smallpox/index.asp. Accessed June 17, 2009.
- Hildreth C. Smallpox. Journal of the American Medical Association. 2009;301:1086.
- Friedman HM, et al. Smallpox. http://www.uptodate.com/home/index.html. Accessed June 17, 2009.
- Smallpox. World Health Organization. http://www.who.int/mediacentre/factsheets/smallpox/en/. Accessed June 17, 2009.
- Taub D, et al. Immunity from smallpox vaccine persists for decades: A longitudinal study. The American Journal of Medicine. 2008;121:1058.
- Rotz L, et al. Smallpox and bioterrorism. In Mandell, Bennett, & Dolin: Principles and Practice of Infectious Diseases. 6th ed. Philadelphia, Pa: Elsevier; 2005. http://www.mdconsult.com/das/book/body/143878763-2/0/1259/0.html. Accessed June 17, 2009.
- Varicella disease questions & answers. Centers for Disease Control and Prevention. http://www.cdc.gov/vaccines/vpd-vac/varicella/dis-faqs-gen.htm. Accessed June 18, 2009.
