The Science of Smallpox

The smallpox virus is a bomb. Variola major is large, spiky, and brick-shaped. Like all viruses, it needs to grow inside a host cell, which, unfortunately, humans provide. Other animals also have pox viruses, including cowpox, monkeypox, and even insectpox.

Smallpox is very contagious, and that's why it is considered a “Category A” bioterrorist threat by the Centers for Disease Control and Prevention (CDC) in Atlanta, GA. You could get it by just standing next to somebody who has it. It's that dangerous! But don't worry—smallpox has been eradicated from the human population. However, it has not been wiped off the Earth. The virus has been stored in deep-freezers in America and Russia and probably other countries, too. It could be a potent biological weapon.

The Biology of Smallpox

Smallpox is spread when a person breathes it in…and out. The virus gets inside the cells lining the throat and hijacks the cellular machinery to make millions more smallpox viruses. The cells explode, releasing smallpox “bombs.” Those virus particles go on to infect other cells in the body. After a week, the person gets a high fever. Then comes the rash—red, itchy spots that grow into blisters. After another week, the blisters dry and crack and turn into scabs. A month later, the scabs fall off, leaving deep pits in the skin. The good part is that the person will never suffer from smallpox again—if he or she survives.

The bad part is that the infected person can die. How? From all those exploding cells. Remember that your body is an organized collection of different types of cells. If one cell is damaged, that's not a problem. But when millions of cells are damaged and entire organs are destroyed, you fall apart from the inside out. And that's exactly what happens in the most severe cases of smallpox. It's a gruesome way to die.

Unfortunately, the smallpox virus doesn't die with the death of its host. Blood carries the virus to its next victim. The scabs of victims are full of virus. The victim's clothes and beds are infectious for days or even months.

The Fight Against Smallpox

People noticed that survivors of smallpox never got it again. So some deliberately tried catching a milder version of smallpox called Variola minor. This process was called variolation and protects the person from getting the more severe form of the disease. Although it saved many lives, this practice also kept the virus in the population.

Edward Jenner was an English country doctor in the late 1700s who knew his patients well. He was a kind and caring man who took the trouble to listen to his patients. A milkmaid once told Jenner that she did not fear smallpox because she already had had cowpox. This idea stayed with Jenner for a long time. He talked about it with several doctors, but they didn't want to believe some old wives' tale about cows and milkmaids.

A decade later, when there was a simultaneous outbreak of cowpox and smallpox, Jenner decided to test the hypothesis that an infection of cowpox could prevent smallpox. Sarah Nelmes, a milkmaid, came down with cowpox. Jenner collected some of the pus from the blister and “vaccinated” James Phipps, a boy of eight. He used the term “vaccination” to distinguish it from “variolation,” because “vacca” is “cow” in Latin. A couple of months later, he tried inoculating the boy with the mild form of smallpox. The boy resisted it—he did not get smallpox!

Jenner published his findings from numerous cases, but people didn't believe him. They were afraid of vaccination. They thought that a blister from a cow could turn them into a cow. Others saw it as tampering with nature. Ultimately, people saw that vaccination was safe, and in the early 1800s the practice spread all over Europe and eventually the world.

The Eradication of Smallpox

In 1967, the World Health Organization (WHO) took it upon itself to rid the world of smallpox. Instead of trying to vaccinate everybody, they used a method of vaccination combined with isolation. That is, when they found someone with smallpox, they vaccinated everybody who had or could come in contact with that person. In addition, they isolated the sick person until that person was no longer infectious. This method worked.

We won the war on smallpox. In 1980, WHO declared “the world and its people” free from smallpox. The virus had one fatal flaw: It could use only one host—humans. Once the chain of infection was broken, there was nowhere that the virus could hide.

The Demon in the Freezer

Smallpox remains in freezers—for research purposes. And, for deadly purposes. Throughout history, smallpox was used as a weapon. Today, most of us have no experience with pox viruses. We are now like the Aztec or Inca long ago. If someone were to unleash one upon us, most of us would die.

In light of the terrorist attacks on September 11, 2001, the U.S. government is preparing for a possible smallpox attack. Large quantities of vaccines are being made. Our military troops and frontline medical teams that would respond in an attack have been vaccinated. Doctors are learning to recognize smallpox. If there is an outbreak, you and your family will have to make tough decisions. Will you get vaccinated? Will you be willing to be isolated if you catch the disease? Will you give up your civil liberties for the greater good of this world?

Let us hope that those decisions will not be necessary. Let us hope that no one will undo one of the great achievements of science and humanity.


  • biological weapon: A biological agent, such as a virus, used in an attack.
  • eradicated: To have gotten rid of.
  • immunity: The ability to resist disease.
  • replicate: To make identical copies.

Back to Top


  1. The article talks about the development and use of vaccinations for smallpox. In order to attend most schools, a student must have received a certain set of vaccinations. Find out what vaccinations your school or district requires. Have you received any vaccinations in addition to the ones required by your school or district? Write down the name of each vaccination you have received.
    [anno: Answers should include a list of vaccinations required by the school or district and any additional vaccinations received by the student.]
  2. What do you think would happen if students weren't vaccinated against certain diseases? What if a student came to school with a case of the measles? Think about the physical environment at school. Write a sentence or two explaining what you think might happen if students weren't vaccinated against certain diseases and an infected student came to school.
    [anno: Answers may vary but could include that if a student is infected with a highly contagious disease and attends school, that student could put many other students at risk for catching the disease since students are often in close proximity with one another.]