For centuries, epidemics of smallpox — an infection caused by the variola virus — affected people all over the globe, and the disease was often serious. But in 1796, British doctor Edward Jenner discovered a way to protect people from getting smallpox, which led to the development of the first smallpox vaccine.

The vaccine worked so well that the United States stopped vaccinating the general population against smallpox in 1972 because the disease was no longer a threat (the last U.S. case of smallpox was in 1949).

The world's last known case of smallpox was reported in Africa in 1977. In 1980, the World Health Organization (WHO) announced that smallpox was wiped out — the first (and only) time in history that an infectious disease was declared eliminated from the planet.

Worries About Smallpox

Although smallpox infection was wiped out many years ago, samples of the variola virus that causes smallpox were saved in laboratories. Some people have expressed concern that terrorists could try to get access to these stored virus samples with the aim of spreading smallpox infection.

Despite talk about the possibility of terrorists spreading smallpox as a biological weapon, the reality is that this probably wouldn't happen for a couple of reasons. First, terrorists would need access to the virus samples, and the few research laboratories that keep them have security measures to guard them. Also, it would be extremely difficult for a group to take the time to produce a large amount of the variola virus without being detected.

The smallpox vaccine also would prevent the spread of disease because it can:

• prevent people from becoming infected if they're vaccinated quickly after exposure to the virus
• make the illness less severe in people who do become infected if they're vaccinated within a few days

Vaccines Could Halt an Outbreak

After the September 11, 2001, terrorist attacks and the anthrax scare that same year, the U.S. government took the precaution of asking several companies to begin making smallpox vaccine again. Today, there's enough vaccine on hand to protect the American people in the event of a smallpox outbreak.

Public health officials have a rapid response plan ready to vaccinate anyone exposed to the disease, as well as people who come into contact with them. So although a person doesn't need to get vaccinated at the moment, the vaccine is there in case it's needed.

Given that the vaccine can stop the spread of the disease, experts believe it's unlikely that terrorists will go to the trouble of producing and using smallpox as a biological weapon — it would take too long and have little effect.

Smallpox Infections

If someone becomes infected with smallpox, it may take anywhere from 7 to 17 days for symptoms to develop. At first a person may have flu-like symptoms such as high fever, fatigue, headaches, and backaches.

Within 2 to 3 days after symptoms start, a rash develops that typically affects the face, legs, and arms. It starts with red marks that become filled with pus and crust over. Scabs develop and then fall off after about 3 to 4 weeks.

Smallpox is very contagious, particularly during the first week a person has the rash. It is most commonly spread in infected drops of saliva when people cough or sneeze. Someone is contagious until after all the scabs have fallen off.

What Works Against Smallpox?

Antibiotics don't work against viruses — they're only effective against bacteria — so taking them won't help someone with smallpox. Vaccination is the only effective weapon against the spread of smallpox. Immunization successfully wiped out smallpox before and, should it become necessary, can help stop any future outbreaks. Researchers are also working to develop other treatments, too.

It's very unlikely that you or your child will ever be exposed to the virus that causes smallpox. But if you're worried about it, talk to a medical professional, who can help you find the answers to any questions you may have.

Reviewed by: Steven Dowshen, MD
Date reviewed: January 2013