Questions and Answers About Smallpox Disease

What should I know about 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. In 1980, the disease was declared eradicated following worldwide vaccination programs. However, in the aftermath of the events of September and October, 2001, the U.S. government is taking precautions to be ready to deal with a bioterrorist attack using smallpox as a weapon. As a result of these efforts: 1) There is a detailed nationwide smallpox response plan designed to quickly vaccinate people and contain a smallpox outbreak. This plan includes the creation of smallpox health care teams that would respond to a smallpox emergency and the vaccination of members of these teams. 2) There is enough smallpox vaccine to vaccinate everyone who would need it in the event of an emergency.

What are the symptoms of smallpox?
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 three weeks, leaving a pitted scar.

Is smallpox fatal?
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.

Is there any treatment for smallpox?
There is no proven treatment for smallpox disease. Prevention is achieved through vaccination. For purposes of controlling a smallpox outbreak, smallpox vaccine and antivirals can be used.

How is smallpox spread?
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.

When are cases of smallpox infectious?
A person with smallpox is sometimes contagious with onset of fever (prodrome phase), but the person becomes most contagious with the onset of rash. The infected person is contagious until the last smallpox scab falls off.

If people had smallpox previously and survived, are they immune from the disease?
Yes. If they had smallpox before and survived, they are immune to the disease.

What if I had been exposed to smallpox previously, but did not contract the disease? Am I immune from the disease?
Just because you were exposed to smallpox does not mean that you were necessarily exposed and infected. The only way that one becomes immune to the disease is by natural disease (development of rash) and by successful vaccination, although the vaccination does not provide life-long immunity.

If someone is exposed to smallpox and is vaccinated within 3 days of exposure, how can this overcome the variola that may be replicating, when it takes 2-3 weeks to build up immunity?
The incubation period of smallpox averages 12 days. Antibodies begin to be produced following vaccination in about a week. It is likely that vaccine-induced antibodies neutralize variola virus before it can cause significant illness. Many observational studies during the eradication program showed that vaccination within 3 or 4 days of exposure could abort or significantly reduce the severity of smallpox disease, whatever the immunology may be.

Is the rash in generalized vaccinia, progressive vaccinia similar to the rash in smallpox?
Generalized vaccinia is a breakout of lesions that looks similar to smallpox. It is the result of the systemic spread of virus from the vaccination site. Despite the appearance of the lesions, it is usually a mild complication after someone gets the vaccine for the first time. Before the eradication of smallpox, the rash of generalized vaccinia had been confused with smallpox. Typically, the rash of generalized vaccinia will evolve and remit more quickly than that of smallpox.

How serious is the smallpox threat?
The deliberate release of smallpox as an epidemic disease is a remote possibility, and the United States is taking appropriate precautions. 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.

How do we expect a smallpox attack to occur, if one happens?
The deliberate release of smallpox as an epidemic disease is now regarded as a possibility. We can’t say with certainty how an attack might occur, but we do know how smallpox is normally transmitted. Transmission most often occurs through person-to-person contact, more rarely through contact with materials contaminated with the smallpox virus, rarely through airborne contagion in enclosed settings. Because an attack could have such serious consequences, every effort is being made to prepare for such a possibility even though it is unlikely to ever occur. These preparedness efforts therefore include use of the best way to prevent smallpox: vaccination.

Page last reviewed: March 13, 2009