Next April 12th may be a day of special convergence, between the past and the future. Historically, it will mark the 50th anniversary of the Salk polio vaccine—specifically, the announcement at the University of Michigan that the vaccine worked. Randall Kerr, a second-grader in Fairfax, VA, was the first person in that clinical trial; 1.8 million children later, the results for safety and efficacy were in, and the rejoicing began. For the future, the same day may be the date when poliomyelitis ceases to exist as a wild type human disease. World health authorities have whittled away the outbreak areas until only a few in Africa remain. Polio is gone from the Amazon's jungles, New Guinea's highlands, and India's remotest village. A few cases have arisen from the live virus, oral vaccine (Sabin) among people with diminished immune systems, but because most of humanity has been immunized, the virus has nowhere to spread. As with the eradication of smallpox, when the last afflicted person is found, eradication has reached the beginning of the end. After a few years of continued vaccination, close surveillance, and no further cases, poliomyelitis will be finished—having existed since the times of the Pharaohs.

Already, polio is mostly forgotten. Young people today have no memory of iron lungs, swimming pools closed because of the epidemic, or the paralyzing fear that swept neighborhoods when a child came down with the disease. Actually, polio was not terribly virulent. At its worst, in 1952, polio's mortality rate was only thirteen per 100,000 population (cancer mortality, today, by comparison is 167.8 per 100,000). While the virus spread widely, 95% of those infected showed no signs, and of the 5% who did present symptoms, only a small number became paralyzed or died. On the other hand, about 20,000 serious cases annually in the early 1950's outnumbered our "9/11" atrocity, and because the disease crippled far more than it killed, the patient population accumulated year after year during the early phase of the "baby boom." Polio-survivors, by 1990, were a driving force behind the Americans with Disabilities Act. Every community with side walks now has a "monument" to polio in its curb cuts.

Jonas Salk (1914-1995) and Albert Sabin (1906-1993) are the polio story's best-known heroes. Neither of them referred to their vaccines by their own names—those were the monikers journalists bestowed—"Salk" for the killed virus vaccine, and "Sabin" for the weakened live-virus vaccine. Both donated their discoveries for the public good.

Because Jonas Salk used formaldehyde to denature polio virus there was little risk of his vaccine causing the disease if it was manufactured properly. Its disadvantage was that only people who received an injection were protected. Albert Sabin, like Louis Pasteur, grew the virus in a succession of animals, thereby weakening it for infecting people. But because Sabin's oral vaccine lived for about two weeks in a child's intestines, where it shed into diapers with a good possibility of reaching other people, vaccination spread in the same manner as the disease. Fear that the live virus vaccine might cause polio prevented Sabin from conducting a large scale clinical trial in the United States; so he organized a massive trial in the Soviet Union and Poland (115 million people, at the height of the Cold War). This experiment abroad opened the way for oral polio vaccine use in the United States after 1962. The vast majority of humanity has been immunized with Sabin's vaccine, but now, with the last few cases, safer Salk's vaccine is doing the mopping up. Polio eradication would not have been conceivable without both.

Neither Salk nor Sabin won the Nobel Prize for their vaccines. That may have been partly due to the extreme animosity between them and their camps. From a scientific standpoint, though, the vaccines were afterthoughts—something the Nobel committee could have assumed would happen after researchers learned how to grow the virus in sufficient quantity to make either vaccine. The Nobel Prize for Physiology or Medicine for growing polio virus went to the Harvard team of John Enders, Thomas Weller and Frederick Robbins in 1954, a year before results of the Salk vaccine clinical trials were known.

When Enders, Weller and Robbins first carried out their prize-winning research, they were investigating chickenpox virus, attempting to grow it in human embryonic tissue. With "left-over" skin and muscle from an abortus of four months gestation, which was terminated because of rubella in the third month, Weller recorded using it to grow polio virus on March 30, 1949. It was not illegal to use human embryonic tissue in medical research at that time, though abortions were illegal; Robbins said, however, they had no trouble acquiring embryonic tissue from several hospitals in Boston. Technically, the advantage of using embryonic tissue was the low risk of contamination from other viruses, which then might naturally recombine with the virus being grown and cause unforeseen complications. Once they found polio virus grew in embryonic tissue, they then succeeded with growing it in human kidney (removed from children suffering with hydrocephalus), and finally with embryonic monkey kidney tissue which opened a way for mass vaccine production.

In the first instance, the example of polio is that Enders, Weller and Robbins had no idea of where their research with embryonic tissue would lead. They did not know if their experiment would work until they tried. Once they realized polio virus grew, they did not know how or why. Genomic and proteomic knowledge came a generation later. They may have foreseen the vaccine potential, but they could hardly have imagined global eradication—though Weller, who lives in Needham, MA today—may see that incredible accomplishment. Ultimately, the example of polio is that human embryo research is the only medical technology, besides using cowpox virus to cross immunize against smallpox, which has benefited every human being alive today, through either vaccination against the disease or from living in a polio-free world. The example should not be forgotten.