Thousands of years ago, smallpox virus, also known as variola virus, emerged from an unknown origin and began causing illness and deaths in human populations, with outbreaks of the virus occurring from time to time. It was one of the world's most devastating diseases known to humanity. The last known natural case was in Somalia in 1977. It was declared eradicated in 1980 following a global immunization campaign led by the World Health Organization.

The clinical definition of smallpox is an illness with acute onset of fever equal to or greater than 38.3 °C (101 °F) followed by a rash characterized by firm, deep seated vesicles or pustules in the same stage of development without other apparent cause.

Before smallpox was eradicated, it was a serious infectious disease caused by either of variola major or variola minor viruses. Variola virus is a member of the orthopoxvirus family.

Smallpox is thought to date back to the Egyptian Empire around the 3rdcentury BCE (Before Common Era), based on a smallpox-like rash found on three mummies.

Transmission of Smallpox

How it spreads:

By blood products (unclean needles or unscreened blood).

By airborne respiratory droplets (coughs or sneezes).

By skin-to-skin contact (handshakes or hugs).

By saliva (kissing or shared drinks/toothbrush).

Before smallpox was eradicated, it was mainly spread by direct and fairly prolonged face-to-face contact between people. Smallpox patients became contagious once the first sores appeared in their mouth and throat. They spread the virus when they coughed or sneezed and droplets from their nose or mouth spread to other people. They remained contagious until their last smallpox scab fell off.

These scabs and the fluid found in the patient’s sores also contained the variola virus. The virus can spread through these materials or through the objects contaminated by them, such as bedding or clothing.

Rarely, smallpox has spread through the air in enclosed settings, such as a building.

Smallpox can be spread by humans only. Scientists have no evidence that smallpox can be spread by insects or animals.

Once a person is infected with the virus, 7 to 17 days can pass before they have any symptoms. During this time, the person isn’t contagious and can’t spread the virus to others.

An infected person is most contagious once they start having symptoms. He can spread smallpox to others until he is completely symptom-free.

What are Smallpox Signs and Symptoms?

The first symptoms of smallpox usually appear 7 to 17 days after you're infected. During the incubation period of 7 to 17 days, you look and feel healthy and can't infect others.

Following the incubation period, a sudden onset of flu-like signs and symptoms occurs. These include:

  • Fever

  • Overall discomfort

  • Headache

  • Severe fatigue

  • Severe back pain

  • Vomiting, possibly

A few days later, flat, red spots appear first on your face, hands and forearms, and later on your trunk. Within a day or two, many of these lesions turn into small blisters filled with clear fluid, which then turns into pus.

Scabs begin to form eight to nine days later and eventually fall off, leaving deep, pitted scars.

Lesions also develop in the mucous membranes of your nose and mouth and quickly turn into sores that break open.


Chickenpox was commonly confused with smallpox in the immediate post-eradication era. Chickenpox and smallpox can be distinguished by several methods. Unlike smallpox, chickenpox does not usually affect the palms and soles. Additionally, chickenpox pustules are of varying size due to variations in the timing of pustule eruption: smallpox pustules are all very nearly the same size since the viral effect progresses more uniformly. A variety of laboratory methods are available for detecting chickenpox in evaluation of suspected smallpox cases.

In contrast to the rash in smallpox, the rash in chickenpox occurs mostly on the torso, spreading less to the limbs.

When smallpox was common, experienced clinicians made the diagnosis simply by looking at the rash and examining the patient.

Any case that occurs now will likely be a result of bioterrorism or biological warfare and in any of such events, misdiagnosis or delays in diagnosis could cause the infection to spread. Thus, it is still important for clinicians to be able to diagnose smallpox.

Even one confirmed case of smallpox would be considered an international health emergency. The Centres for Disease Control and Prevention can do definitive testing using a tissue sample taken from one of the lesions on the skin of the infected person.


There is no proven treatment for smallpox disease, but some antiviral drugs may help treat it or prevent it from getting worse. Treatment would focus on relieving symptoms and keeping the person from becoming dehydrated. Antibiotics might be prescribed if the person also develops a bacterial infection in the lungs or on the skin.

There also is a vaccine to protect people from smallpox. If there were a smallpox outbreak, health officials would use the smallpox vaccine to control it.

The smallpox vaccine

Smallpox can be prevented by the smallpox vaccine.

If you get the vaccine:

  • Before contact with the virus, the vaccine can protect you from getting sick.

  • Within 3 days of being exposed to the virus, the vaccine might protect you from getting the disease. If you still get the disease, you might get much less sick than an unvaccinated person would.

  • Within 4 to 7 days of being exposed to the virus, the vaccine likely gives you some protection from the disease. If you still get the disease, you might not get as sick as an unvaccinated person would.

Once you have developed the smallpox rash, the vaccine will not protect you.

Currently, the smallpox vaccine is not available to the general public because smallpox has been eradicated, and the virus no longer exists in nature.


Most people with smallpox recovered, but about 3 out of every 10 people with the disease died. Many smallpox survivors have permanent scars over large areas of their body, especially their faces. Some are left blind.

How to Avoid Getting Smallpox

To lower your risk of getting sick if terrorists release smallpox virus on purpose:

  • Stay informed. Listen to the news to learn how the emergency is affecting your community and what actions SFDPH recommends people take.

  • If you were exposed to a suspicious substance or if you were in an area thought to contain smallpox virus, it may help to wash your skin and hair thoroughly with soap and water. It may also help to change and wash your clothing or to put them in a plastic bag to keep them separate from your other things.

  • Stay away from, and keep your children away from, anyone who might have smallpox.

  • Avoid being in enclosed areas with others who may be sick, such as buses and trains.

  • Do not touch the skin area where someone had a smallpox vaccine placed.

  • Wash your hands regularly and avoid touching your eyes, nose, and mouth.

If you were vaccinated as a child

Immunity or partial immunity after a smallpox vaccine may last up to 10 years, and 20 years with revaccination. If an outbreak ever occurred, people who were vaccinated as children would still likely receive a new vaccination after direct exposure to someone with the virus.

Smallpox Facts
  • Smallpox is a contagious disease caused by the variola virus.

  • Smallpox was the first disease to be eliminated from the world through public-health efforts and vaccination.

  • Smallpox still poses a threat because existing laboratory strains may be used as biological weapons.

  • Smallpox causes high fever, prostration, and a characteristic rash. The rash usually includes blister-like lesions that occur everywhere on the body.

  • Approximately one-third of people with smallpox died from the disease. Survivors were scarred for life. If the eye was infected, blindness often resulted.

  • There are new experimental medications that might be effective in smallpox, but these have not been tested in human cases since the disease has been eradicated.

  • The smallpox vaccine contains a live virus called vaccinia. It is administered by dipping a pronged piece of metal into the vaccine and then pricking the skin.

  • The vaccine has uncommon side effects that may be fatal, including infection of the heart and brain with the vaccinia strain. Serious side effects are more common with the initial vaccine and are uncommon with second doses.

  • The vaccine is currently only given to selected military personnel and laboratory workers who handle the smallpox virus.

Smallpox research continues and focuses on the development of vaccines, drugs, and diagnostic tests to protect people against smallpox in the event that it is used as an agent of bioterrorism or biological warfare.

....making effort to "STAY WELL"



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