For Sabin, the problems were three: safety, efficacy, and practicality. Early on, Sabin held that one particular strain Salk had used–a highly virulent strain called Mahoney – would be hard to kill and thus dangerous. The question of efficacy was whether any killed-virus vaccine could produce lifelong immunity. And finally, even though the vaccine did stimulate production of antibodies, three shots were necessary, plus a later booster. Sabin put the point most succinctly: “The need for inoculating large amounts and the need for repetition are bad.” In contrast, an oral vaccine with a small dose of the attenuated versions of each of the three strains, administered once, would give lifelong immunity.
Then came the shock of the Cutter incident. On April 24, 1955, just days after the Salk vaccine went into use, polio broke out among children who had received shots from a batch made by Cutter Laboratories in California. Eleven died. It is usually asserted that the Cutter incident was caused by particular lots of vaccine that still contained live polio virus, but the presence of the live virus has never been satisfactorily explained. Joshua Lederberg, who received a Nobel Prize in 1958 for his work in bacterial genetics, was involved in polio-virus research in the early 1950s. Lederberg told me in March 2002 that the Cutter incident is “still a little bit of a mystery.” The virus strains in the Salk vaccine were inactivated with formaldehyde. Lederberg said that the chemistry of the formaldehyde-virus interaction has never been adequately studied. “It is my opinion that under some conditions, it is a reversible reaction,” he said. “In fact I know that it is.” He went on, “The question is [with] what reagents or under what conditions a formaldehyde will come off the inactivated complex and thus restore its infectivity.” And so, Lederberg said, because nobody understood the reasons for the “Cutter catastrophe,” research continued into alternatives to the Salk vaccine. (After the Cutter incident, production methods were changed. No further safety problems with the vaccine have been reported.)
The force behind Salk and his vaccine was the National Foundation for Infantile Paralysis – later rechristened the March of Dimes – and in particular its president, Basil O’Connor, who was not a scientist. In an interview in 1984, Salk said, “I would say that the fact that the vaccine became available in 1955 was attributable to the existence of Basil O’Connor, that without him the story would have been quite different….He had it within his power to cause almost anything to happen.” As Sabin dug deeper into his vaccine research, he began openly to oppose the foundation, for he believed it ignored important scientific conclusions and was unrealistically pushing for a quick solution.
Sabin was particularly critical of O’Connor, charging that he was biased. In a letter dated June 25, 1955, he asked O’Connor, “Would it not be better if you as President of the National Foundation of Infantile Paralysis observed a more impartial attitude regarding the scientific work and contributions of all scientists whose work is supported by the donations from the American people through the Foundation which you so ably lead?” On August 1, in another letter, Sabin attacked O’Connor’s interpretation of safety: “A killed-virus vaccine for poliomyelitis must be safe without qualifications. If it is admitted that it can be made safer, then it is not sufficiently safe.” He referred to the Cutter incident: “When such a tragedy occurs you do not continue operations as usual.”