Though the controversy surrounding the nationwide decision to reinstate the smallpox vaccine is recent, the history of the virus and its vaccine is extensive.

Today, as in the past, vaccination is effectively the only way to control smallpox, which has no cure, said Steven Keating, instructor in biochemistry and molecular biology.

After the virus has been contracted, "either your immune system wins, or the virus wins," he said. "You get rid of it with your own immune system, or you die."

The smallpox vaccine was the first vaccine ever developed, said Michael Teng, assistant professor of biochemistry and molecular biology.

In the late 1700s, physician Edward Jenner noticed that milkmaids tended to be protected from smallpox, Teng said. Jenner found that they were actually immune because they commonly contracted cowpox, a close cousin of smallpox.

Their subsequent immunity to this far less dangerous disease also protected them from the lethal smallpox, Teng said. This knowledge allowed Jenner to create the first smallpox vaccine.

Through the process of vaccination, smallpox became effectively eradicated in 1980, and vaccination was discontinued in 1972, Teng said. The last known case of smallpox occurred in 1977.

The smallpox vaccine is a live one, said Andrea Mastro, professor of microbiology and cell biology. As with any live vaccine, patients are injected with a weakened version of the disease itself.

Because of this, there is a small risk that the vaccine will make people sick, she said.

"As with any vaccine, there's always some chance it will cause some sort of reaction," she said.

Teng said these side effects can be very serious for approximately one or two out of a million people, and can even prove fatal.

It is for this reason that vaccination was discontinued in the first place, and why many authorities are reluctant to reinstate the vaccine, he said.

Some of the symptoms of smallpox include fever, headache and rash, he said.

In addition, the characteristic manifestation of smallpox is a pox, which is the appearance of red, raised pustules on the skin, he said.

These pustules appear most often on the face and extremities, Keating said.

If the victim recovers, these areas will often scab over and result in scarring, he said.

One of the main ways smallpox, which is highly contagious, is transmitted is when these pustules form on the inside of the throat, he said. When the victim coughs, he or she spreads droplets loaded with the smallpox virus into the air.

"The most common way it is spread is coughing [these droplets] into the air," he said.

There are different opinions as to what actually causes a smallpox death, he said.

Some people believe that death is ultimately caused by organ failure. Others think it is a result of an overreaction of the immune system, while still others believe death is eventually caused by pneumonia, the filling of the lungs with fluid.

In any case, the disease is quite deadly. It has up to an 80 percent mortality rate, Teng said.

"It is something that used to kill a very large percentage of the population," Keating said. "It's always been a significant killer, even in the 20th century."

Though there currently is no cure for smallpox, there are antiviral drugs under development now, Keating said. However, it is difficult to test these drugs, because smallpox is unique to humans and generally cannot be studied in other species.

"Naturally, it only affects humans, which is a problem for research. Where are you going to test your drug?" he said.

Researchers face other problems as well, he added.

"The problem is, there's no way to directly test this in humans because nobody has smallpox," he said.

So for now, vaccination remains the only answer.

"It's the defense we know would work," he said.