Smallpox & Bioterrorism

Smallpox is a bioterrorist threat.

Smallpox & Bioterrorism

Smallpox, because of its high case-fatality rates and transmissibility, now represents one of the most serious bioterrorist threats to the civilian population. Smallpox is considered a category A biological disease. Category A biological diseases are considered high-priority agents that include organisms that pose a risk to national security because they:

  • can be easily disseminated or transmitted person-to-person; 
  • cause high mortality, with potential for major public health impact; 
  • might cause public panic and social disruption; 
  • and require special action for public health preparedness. 

Smallpox is one of these such organisms. Here are some facts about smallpox you should know.

Smallpox infection was eliminated from the world in 1977.

Smallpox is caused by variola virus. The incubation period is about 12 days (range: 7 to 17 days) following exposure. Initial symptoms include high fever, fatigue, and head and back aches. A characteristic rash, most prominent on the face, arms, and legs, follows in 2-3 days. The rash starts with flat red lesions that evolve at the same rate. Lesions become pus-filled and begin to crust early in the second week. Scabs develop and then separate and fall off after about 3-4 weeks. The majority of patients with smallpox recover, but death occurs in up to 30% of cases.

Smallpox is spread from one person to another by infected saliva droplets that expose a susceptible person having face-to-face contact with the ill person. Persons with smallpox are most infectious during the first week of illness, because that is when the largest amount of virus is present in saliva. However, some risk of transmission lasts until all scabs have fallen off.

Routine vaccination against smallpox ended in 1972. The level of immunity, if any, among persons who were vaccinated before 1972 is uncertain; therefore, these persons are assumed to be susceptible.

Vaccination against smallpox is not recommended to prevent the disease in the general public and therefore is not available.

In people exposed to smallpox, the vaccine can lessen the severity of or even prevent illness if given within 4 days after exposure. Vaccine against smallpox contains another live virus called vaccinia. The vaccine does not contain smallpox virus.

The United States currently has an emergency supply of smallpox vaccine.

There is no proven treatment for smallpox but research to evaluate new antiviral agents is ongoing. Patients with smallpox can benefit from supportive therapy (intravenous fluids, medicine to control fever or pain, etc.) and antibiotics for any secondary bacterial infections that occur.



  1. MedicineNet


Medically reviewed by John A. Daller, MD; American Board of Surgery with subspecialty certification in surgical critical care August 1, 2017

Provided with the kind permission of the Centers for Disease Control.

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