Fifty years ago, a worldwide polio epidemic was in full swing. More than 58,000 cases were reported in the United States alone in 1952, primarily among children. Fear of this highly infectious and crippling disease was spreading panic through communities across the country.

John Brown remembers being scared. When he was six years old, his little brother was taken away. Two weeks later, he was taken to Municipal Hospital in Pittsburgh and put into a bed beside his brother. The two had polio, and so did the dozens of other children in the ward. No visitors were allowed to see the children. Starved for affection, John Brown remembers a dark-skinned ward attendant named Mrs. Moore. "She was probably the nearest thing to an angel that I will ever see," he says. "I remember that she would call us her precious babies, and would tell us how much our parents loved us." The two boys spent months alone in the hospital. Groups of doctors often came through the ward. Some of the children got to visit their laboratory on another floor. John was not one of them. "We were told that there was a floor in the hospital that was full of monkeys and that we were acting just like the monkeys."

Jonas Salk was the doctor in charge of that upstairs laboratory. He says his team grew the polio virus in tissue culture and then injected it into monkeys. "It started small: First in a few animals, then more animals, then in a few people, and then in more people," he says. "And eventually there was a large-scale field trial that was carried out by Dr. Thomas Francis, Junior at the University of Michigan in 1954 and completed in 1955, involving 1,800,000 children."

None of those children contracted polio. So, on April 12, 1955, it was announced that there was a safe, effective and potent polio vaccine. As it became available worldwide, the number of polio cases plummeted. The vaccine helped stop the virus in its tracks, in the United States and in much of the world.

Gary Nabel, director of the Vaccine Research Center for the National Institutes of Health, says Dr. Salk and his team carefully and systematically investigated the virus. The researchers used an inactive polio virus to create the vaccine. "It was really that mimicry of the virus that caused the disease, [in] a form of it that was not lethal," he explains, "that allowed the vaccine to succeed." The Salk team also had to figure out which strains of the virus were relevant and which were not. One researcher - John Enders - developed a technique to propagate polio virus in embryonic cells. He would later receive a Nobel Prize in medicine for the work.

In addition to stopping the polio epidemic in its tracks, Mr. Nabel says the Salk vaccine also demonstrated that medical research could provide a critical tool that might one day rid the world of some of its most terrible diseases. "It ... really showed us how powerful a vaccine can be as a tool for promoting public health, not only for diseases like polio, but for all kinds of other pathogens that threaten us," he says. "So I think that probably the two major legacies are the fact that we don't have to worry about a disease that was truly a scourge, and two, it provided an example to guide us to the same place for other diseases."

The last case of polio in the United States was reported in 1979. The U.N. Children's Fund, UNICEF, reports that worldwide, only 64 cases remain, mostly in Africa. A massive U.N.-led program to eradicate polio is underway across the continent and is expected to immunize as many as 100 million African children.