What is smallpox?

Smallpox is an acute, contagious, and sometimes fatal disease caused by the variola virus (an orthopoxvirus), and marked by fever and a distinctive progressive skin rash. The name smallpox is derived from the Latin word for “spotted” and refers to the raised bumps that appear on the face and body of an infected person. In 1980, the disease was declared eradicated following worldwide vaccination programs. However, in the aftermath of the events of September and October, 2001, the US government is taking precautions to be ready to deal with a bioterrorist attack using smallpox as a weapon. As a result of these efforts, there is a detailed nationwide smallpox response plan designed to quickly vaccinate people and contain a smallpox outbreak and that includes the creation of smallpox healthcare teams that would respond to a smallpox emergency and the vaccination of members of these teams. Also, there is enough smallpox vaccine to vaccinate everyone who would need it in the event of an emergency.

There are 2 clinical forms of smallpox. Variola major is the severe and most common form of smallpox, with a more extensive rash and higher fever. There are 4 types of variola major smallpox: ordinary (the most frequent type, accounting for 90% or more of cases); modified (mild and occurring in previously vaccinated persons); flat; and hemorrhagic (both rare and very severe). Historically, variola major has an overall fatality rate of about 30%; however, flat and hemorrhagic smallpox usually are fatal. Variola minor is a less common presentation of smallpox, and a much less severe disease, with

The majority of patients with smallpox recover, but death may occur in up to 30% of cases. Many smallpox survivors have permanent scars over large areas of their body, especially their face. Some are left blind.

At the moment, the smallpox vaccine is not available for members of the general public. In the event of a smallpox outbreak, however, there is enough smallpox vaccine to vaccinate everyone who would need it.

Smallpox can be prevented through use of the smallpox vaccine. There is no proven treatment for smallpox, but research to evaluate new antiviral agents is ongoing. Early results from laboratory studies suggest that the drug cidofovir may fight against the smallpox virus; currently, studies with animals are being done to better understand the drug's ability to treat smallpox disease (the use of cidofovir to treat smallpox or smallpox reactions should be evaluated and monitored by experts at NIH and CDC). Patients with smallpox can benefit from supportive therapy (e.g., intravenous fluids, medicine to control fever or pain) and antibiotics for any secondary bacterial infections that may occur.

The symptoms of smallpox begin with high fever, head and body aches, and sometimes vomiting. A rash follows that spreads and progresses to raised bumps and pus-filled blisters that crust, scab, and fall off after about 3 weeks, leaving a pitted scar. After exposure, it takes between 7 and 17 days for symptoms of smallpox to appear (average incubation time is 12 to 14 days). During this time, the infected person feels fine and is not contagious.

High fever (more than 101 degrees Fahrenheit), fatigue, headache and backache begin approximately 12 days after exposure to smallpox virus (range of time for symptom onset is 7-17 days after exposure). One to 4 days after the first symptoms, a rash develops first on the face and arms, followed by the legs and trunk. The rash starts as flat, red spots, and over the next several days, the spots fill with fluid and then pus. The rash begins to form a crust early in the second week of illness, then forms scabs which fall off after about 3-4 weeks. The majority of persons with smallpox recover, but death occurs in up to 30% of cases.

Many smallpox survivors have permanent scars over large areas of their body, especially their face. Some are left blind.

After exposure, it takes between 7 and 17 days for symptoms of smallpox to appear (average incubation time is 12 to 14 days). During this time, the infected person feels fine and is not contagious.

Vaccination within 3 days of exposure will completely prevent or significantly modify smallpox in the vast majority of persons. Vaccination 4-7 days after exposure likely offers some protection from disease or may modify the severity of disease.

Smallpox normally spreads from contact with infected persons. Generally, direct and fairly prolonged face-to-face contact is required to spread smallpox from one person to another. Smallpox also can be spread through direct contact with infected bodily fluids or contaminated objects such as bedding or clothing. Indirect spread is less common. Rarely, smallpox has been spread by virus carried in the air in enclosed settings such as buildings, buses, and trains. Smallpox is not known to be transmitted by insects or animals.

The smallpox vaccine is the only way to prevent smallpox. The vaccine is made from a virus called vaccinia, which is another “pox”-type virus related to smallpox but cannot cause smallpox. The vaccine helps the body develop immunity to smallpox. It was successfully used to eradicate smallpox from the human population.

Routine vaccination of the American public against smallpox stopped in 1972 after the disease was eradicated in the United States. Until recently, the US government provided the smallpox vaccine only to a few hundred scientists and medical professionals who work with smallpox and similar viruses in a research setting. After the events of September and October, 2001, however, the US government took further actions to improve its level of preparedness against terrorism. For smallpox, this included updating a response plan and ordering enough smallpox vaccine to immunize the American public in the event of a smallpox outbreak. The plans are in place, and there is sufficient vaccine available to immunize everyone who might need it in the event of an emergency. In addition, in December of 2002, the Bush Administration announced a plan to better protect the American people against the threat of smallpox attack by hostile groups or governments. This plan includes the creation of smallpox healthcare teams that would respond to a smallpox emergency. Members of these teams are being vaccinated against smallpox. The plan also included vaccination of certain military and civilian personnel who are or may be deployed in high threat areas.

Because the risk of a smallpox outbreak is low and because the smallpox vaccine has serious side effects, including death, smallpox vaccine is not recommended or available for the general public at this time.

An infection occurs when the smallpox virus gets into the mouth, nose, throat, lungs, or eyes. Exposure to smallpox can occur by direct contact with droplets from the respiratory tract (saliva) when an infected person talks, coughs, or sneezes, from direct contact with the smallpox rash, scabs, or drainage from the sores, or by indirect contact when handling objects that have been contaminated by smallpox virus. Persons with smallpox are most contagious when the rash first develops. At this stage the infected person is usually very sick and not able to move around in the community. The person remains contagious until the scabs have disappeared.

The last case of smallpox in the United States was in 1949. The last naturally occurring case in the world was in Somalia in 1977. After the disease was eliminated from the world, routine vaccination against smallpox among the general public was stopped because it was no longer necessary for prevention.

The deliberate release of smallpox as an epidemic disease is now regarded as a possibility, and the United States is taking precautions to deal with this possibility. Public Health, hospitals, and other area health care providers and state and local government are actively working together to prepare and test plans for detecting and responding to smallpox cases. When smallpox is reported to Public Health an immediate and intensive investigation will result. If a smallpox case is likely or confirmed, vaccine will be requested from the federal government to protect persons who have been exposed.

Smallpox is classified as a Category A agent by the Centers for Disease Control and Prevention. Category A agents are believed to pose the greatest potential threat for adverse public health impact and have a moderate to high potential for large-scale dissemination. The public is generally more aware of category A agents, and broad-based public health preparedness efforts are necessary. Other Category A agents are anthrax, plague, botulism, tularemia, and viral hemorrhagic fevers.

One confirmed case of smallpox is considered a public health emergency. The smallpox virus is fragile. In laboratory experiments, 90% of aerosolized smallpox virus dies within 24 hours; in the presence of ultraviolet (UV) light, this percentage would be even greater. If an aerosol release of smallpox occurs, 90% of virus matter will be inactivated or dissipated in about 24 hours.

Smallpox outbreaks have occurred from time to time for thousands of years, but the disease is now eradicated after a successful worldwide vaccination program. The last case of smallpox in the United States was in 1949. The last naturally occurring case in the world was in Somalia in 1977. After the disease was eliminated from the world, routine vaccination against smallpox among the general public was stopped because it was no longer necessary for prevention.

The smallpox virus is fragile. In laboratory experiments, 90% of aerosolized smallpox virus dies within 24 hours; in the presence of ultraviolet (UV) light, this percentage would be even greater. If an aerosol release of smallpox occurs, 90% of virus matter will be inactivated or dissipated in about 24 hours.

People can find more information about smallpox on this page: Smallpox Information