By Bruce Kennedy
CNN Interactive

For the first time in history, mankind has apparently won out over a widespread and lethal disease -- and is closing in on another ancient scourge. But the new century is expected to bring new challenges for immunization specialists.

Just 20 years ago, after a massive international vaccination campaign, the World Health Organization declared it had eradicated smallpox, a disfiguring disease that has a 30 percent fatality rate.

Health officials have now set their sights on polio and hope to have it eradicated within the next several years. Polio may have faded out of the modern public consciousness in much of the world, but for those who lived through the epidemics of the 1940s and '50s, the disease still holds an emotional impact.

Epidemic proportions

Poliomyelitis, also known as infantile paralysis, is a virus that lives in the human digestive system, and most often enters its human host via the mouth. In its mildest form, polio may cause no more than a fever and sore throat, and those infected recover completely. But in about 1 percent of those infected, polio can destroy or cripple muscles needed for movement, swallowing or breathing.

Polio epidemics have swept across the United States several times this century. The first major outbreak was in 1916, when 27,000 people suffered paralysis and 6,000 died. The worst was in 1952, when 58,000 cases were reported and more than 3,000 people died.

Parents, knowing that young children were among those most vulnerable to the disease but not knowing how it was spread, kept their sons and daughters away from playgrounds, pools and other public places. Some parents made their children stay indoors all summer, when polio appeared to be in season.

The media of the time reported and tracked cases of polio the way newspapers now list crime victims. Images of children unable to breathe on their own and encased in so-called "iron lung" respirators added urgency to efforts to find a cure for polio.

'Polio pioneers'

The National Foundation for Infantile Paralysis, which came to be known as the March of Dimes, was founded in the 1930s. Private contributions to the foundation helped finance research that led to the development of a vaccine by Jonas Salk. The vaccine, using killed polio virus, was put to the test on a scale that is unimaginable today.

In 1954, a year after a successful test with a small control group, nearly 2 million U.S. schoolchildren ages 6 to 9 years in 44 states became "polio pioneers."

They were inoculated with either the polio vaccine or a placebo. There had been rumors before the field test that the vaccine was actually fatal. The foundation had to rush out press releases discounting those rumors. There also were fears that Salk and the foundation had moved too quickly with the vaccine.

But on April 12, 1955, after the tests had proved successful, The Associated Press released a bulletin: "The Salk polio vaccine is safe, effective and potent, it was announced today."

90 percent decline

Mass vaccination campaigns followed. In 1957, only 5,000 cases of polio were reported in the United States. In 1961, the introduction of an oral polio vaccine developed by Dr. Albert Sabin further reduced the incidence of polio.

By 1981, only six polio cases were reported in the United States.

On a global scale, polio still exists. But reports of polio fell by almost 90 percent in recent years -- from 350,000 confirmed cases in 1988 to about 35,000 cases in 1997. Polio epidemics still occur and were reported recently in Angola and the Democratic Republic of Congo.

"To summarize it briefly, 150 to 160 countries are polio-free," says Bob Keegan, deputy director of the polio eradication program at the Centers for Disease Control and Prevention, "and we're actively working to get polio eradicated in the last 50 countries."

War and civil unrest, which prevent nationwide vaccination programs from taking place, are the main obstacles to eradicating polio, Keegan says.

Comparisons to AIDS

The conquering of polio has had an unintended side effect, according to some observers.

"Because of the huge success of the polio vaccination program, there's a widespread assumption that AIDS and anything else will be cured by some unknown 'them' who will say, 'Line up, we have the vaccine,'" says Jane S. Smith, author of Patenting The Sun: Polio and the Salk Vaccine. "They forget how much public effort has to go into ending a disease."

As for AIDS, Smith notes certain similarities.

"Each was a disease that seemed to come out of nowhere and achieved epidemic proportions," she says. "Similarly there was a long period of confusion about what caused the disease."

"What may be different between public perceptions of polio and AIDS," notes Keegan, "is that people thought they could control who would get AIDS because it was associated with specific behaviors. With polio, people thought it couldn't be controlled; that anybody, including President Franklin D. Roosevelt, could get the disease. There was a perception that polio was a more random event, and everyone was at risk."

Before his death in 1995 at the age of 80, Salk was actively involved in the search for an AIDS vaccine.

"It's somewhere out there in nature," Salk once said of a possible answer to AIDS. "We just don't know yet what question to ask."

Bioterrorism, plagues pose threat

But some scientific circles are not as optimistic, especially when it comes to mankind's inevitable next brush with an epidemic -- including a possible man-made crisis.

A paper recently issued by the Center for Civilian Biodefense Studies at Johns Hopkins University warns that smallpox, "because of its high case-fatality rates and transmissibility, now represents one of the most serious bioterrorist threats to the civilian population."

"It is possible that smallpox virus fortifies the arsenals of terrorist groups or some nations," the British medical journal The Lancet notes in a May 8, 1999, editorial. "Some experts fear that the release of smallpox virus into the population, whether by mistake or intent, may be only a matter of time."

Live samples of smallpox are now known to exist in only two laboratories -- the Centers for Disease Control and Prevention in Atlanta, and the Russian State Center for Research on Virology and Biotechnology in Koltsovo.

An international controversy has been brewing over whether those centers should destroy their stocks -- or hold on to the samples for future research. In May 1999, the World Health Organization voted to delay destruction until 2002 at the latest.

Dr. Donald A. Henderson, director at the Johns Hopkins center, also warns of future plagues by as-yet-undetermined biological threats.

"We are regularly detecting new viruses, new organisms," he says. "There's a constant process of mutation and change. Because of travel, people moving rapidly, penetrating areas they haven't been before, the large, huge cities people now live in -- there are all sorts of reasons for all sorts of diseases to emerge."