SMALLPOX (Variola virus) FACT SHEET

What is smallpox?

Smallpox is caused by variola virus.  Smallpox infection was eliminated from the world in 1977.

How is smallpox transmitted?

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.

What is the incubation period?

The period is about 12 days (range: 7-17 days) following exposure.

What are the symptoms of smallpox?

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.

What is the period of communicability?

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.  Disease is most often transmitted from the time the ill person first develops rash until the time when rash has resolved (all scabs have fallen off).

Can I go to my doctor and request the smallpox vaccine?

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 the vaccine is not commercially available at this time.

The United States currently has a supply of smallpox vaccine for emergency use, if needed.

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.

Can smallpox be treated?

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