Smallpox is a contagious viral illness caused by the variola virus. The virus can spread from an infected person through the air when there is fairly prolonged (1-3 hours) direct contact. It can also spread via body fluids, either by direct contact with fluids from an infected person or by touching objects that have been contaminated by infected body fluids. The last documented case of smallpox disease occurred in 1977. However, smallpox is still considered a possible biological threat.
An infected person usually begins to experience symptoms 12 to 14 days after exposure. Smallpox disease results in a fever and viral-like symptoms, followed by a rash that progresses from papules to pustules. Eventually the pustules form scabs and the scabs fall off. People with smallpox can spread the virus to others beginning when their fever is 101°F until all their scabs fall off.
There is no proven cure for smallpox. Historically, death has occurred in about 30% of cases. Giving smallpox vaccine soon after exposure to the virus can help to reduce the effects of smallpox disease. Vaccine given within 3 days after exposure can help prevent death. Vaccine given within 7 days after exposure can result in a less severe (modified-type) smallpox illness.
There is only one smallpox vaccine available in the United States. It is a live, attenuated vaccine made from vaccinia virus. Vaccinia virus is closely related to variola virus, which is the virus that causes smallpox. Immunity against vaccinia virus also provides protection against variola virus. It is administered using a bifurcated needle that is jabbed into the surface of the skin.
To reduce the chance of spreading the vaccine virus to other body parts or other people, please follow these recommendations:
Mild reactions include swelling and tender lymph nodes that can last two to four weeks after the blister heals. Most people develop itching, headache, fatigue, muscle aches, pain, or chills after smallpox vaccination, usually about eight to 12 days later. Some individuals may have rashes that last two to four days. These side effects are usually temporary and self-limiting, meaning they go away on their own or with minimal medical treatment, for example aspirin and rest.
If the vaccination is successful, a red and itchy bump develops at the vaccine site in three or four days. Then, in the first week, the bump becomes a large blister and fills with pus. During the second week, the blister begins to dry up and a scab forms. The scab falls off in the third or fourth week, leaving a small scar. People who are being vaccinated for the first time have a stronger reaction than those who are being revaccinated.
If someone does not get the expected vaccination site response, they need to be revaccinated. If someone has a question or concern about the smallpox vaccination site they should contact their primary-care manager, medical department representative or their healthcare provider.