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Salk and Sabin

Brass Tacks

By Peter Cummings

In January, 1955, Albert B. Sabin inoculated 30 volunteers at Ohio's Chillicothe Reformatory, with a weakened strain of live polio virus. Just three months later, Jonas E. Salk announced that he had successfully tested his dead polio virus vaccine on 440,000 elementary school students, and the United States Public Health Service (PHS) licensed six companies to produce the Salk vaccine. Since then U.S. polio cases, both paralytic and non-paralytic, have fallen from 28,985, in 1955, to 650 reported in 1962.

"Live" vs. "dead" vaccine has been an object of medical interest and debate for over a decade. While the United States began to eradicate poliomyelitis in 1955, Dr. Sabin went on with his studies, sending his virus strains for field trials abroad where they would not interfere with the results of the Salk program. At the end of 1959, almost half the U.S. population had received a Salk shot, and already the occurrence of polio had dropped 80%. By the same time, Merck, Sharp, and Dohme Research Laboratories had shipped Sabin's live virus doses to Mexico, Czechoslovakia, Poland, Malaya, Singapore, and the U.S.S.R. Over ten million people were vaccinated in these countries, while in the Belgian Congo 2.2 million took another live virus vaccine, developed by Dr. Herald R. Cox of the Lederle Labs. Still a third live-type preparation was being developed by Dr. Koprowski of the Wistar Institute.

Salk, Sabin, and other authorities and organizations had disagreed on the relative merits of the vaccines, but the dispute remained subdued until the AMA House of Delegates state, in March, 1961, that "the persistence of immunity induced by the oral [Sabin] vaccine may be of much longer duration than is the case with Salk vaccine and, in fact, the persistence of immunity may conceivably approach that induced by natural infection in type, degree, and duration." And while the AMA urged wider use of Salk injections until Sabin was licensed, it noted that the Sabin protects against both paralytic and non-paralytic polio, whereas the Salk only prevents the former, that Sabin oral vaccine is easier to administer than the Salk needle type, and finally that Salk treatment is "80% or more" effective, rather than the "90% or more" which Dr. Salk and the PHS claim.

Sabin Type Declared Safe

Salk protested the AMA statement, accusing it of "misinformation and misleading references," and when he asked why he was not consulted in the matter, the AMA replied that it "wanted experts who were not protagonists." Salk expressed the fear that Sabin protection would simply reintroduce the live virus into the human environment, but Dr. Spring, secretary of the House of Delegates, rejoined that "everyone should get them as extra protection... In our opinion, the more vaccination the safer you are. This does not imply that the Salk vaccine is useless, but it is not perfect and at present a booster shot should be given annually." Although the Salk-AMA exchange ended here, the issue was far from settled.

On August 17, 1961, after over six years of tests, the PHS licensed Pfizer and Co. to produce Type 1 Sabin vaccine and purchased over one million emergency epidemic doses for cold storage at Atlanta's Communicable Disease Center. In March, 1962, the final Type III Vaccine was approved by the government. Then, in September, Canada suddenly suspended its use of the vaccine because four cases of polio had appeared among the 4,000,000 inoculated, and the PHS wished to check the possibility that the Sabin virus had caused the disease. In the U.S. eleven such cases were reported after 38,000,000 inoculations, and the victims had all exhibited symptoms after the use of Type III vaccine. In 1955 a similar situation occurred with 67 polio outbreaks after Salk treatment. Subsequent investigations revealed faulty production of "dead" virus by Cutter Laboratories. (Cutter later had to pay over a million dollars in damages.)

In view of the potential danger, however small, the PHS recommended that communities withhold Type III from adults, yet at the same time urged that all types be given to children. But many Communities decided to stop all Sabin activities and allowed their vaccination programs to flounder despite PHS pleas for more inoculations. These events elicited remarks from Dr. Salk in praise of his vaccine, protests from Sabin, a statement from New York Health Commissioner Hilleboe that he would only permit use of the Salk preparation, and a remark from Dr. Eichenwald of Cornell's New York Hospital insisting that oral vaccine "is safer and more effective against polio than Salk vaccination." Finally a government committee met in mid-December and Surgeon General Terry announced that "because potential risks of [oral] vaccination are believed by some to exist in adults, especially above the age of thirty, vaccination should be used for adults only with the full recognition of its very small risk." In effect this pronounced Type III safe.

A Needle or a Bonbon

In order to properly appraise the value of the two vaccines, one should examine their differences. Both are made from live polio viruses, cultured in test tubes on monkey kidney tissue. In the Salk process, the viruses are heated in formalin, killing them and making them safe for injection into the human blood stream. Fourteen days after the first shot, antibodies appear in the blood, giving a slight amount of protection against all three types of polio virus. Then a booster shot is administered and seven months later another booster, both raising the antibody level. A year later a fourth injection furnishes even more protection, and some authorities urge a booster every year in order to remain safe.

Sabin vaccine is made from "attenuated" live virus, virus which has been bred from selected strains of weak virus. The question has been raised as to the possibility that the weakened virus might mutate back to its wild, virulent state, regaining its deadly ability to attack the human nervous system. It is this question that forced Sabin to prolong his field tests, but today it seems clear that his strains are genetically stable and therefore safe, as now proven in over 140 million vaccinated persons.

The Sabin live virus is taken orally, mixed with a syrup, on a sugar cube, or in a bonbon. Within one day it multiplies in the intestines, preventing the entry of the natural virus and protecting against non-paralytic polio, neither of which the Salk vaccine can do. Although one does of oral vaccine immunizes indefinitely against any one type of virus, three doses are needed for Types I, II, and III. The live virus, while too weak to attack the nerve tissue or produce symptoms of disease, causes the human host to produce the necessary antibodies. Furthermore, the virus retains its capacity to spread contagiously. Thus the inoculation of part of a community can eventually cause the spread of immunity to the entire populace, at the same time preventing the immune person from carrying or spreading the wild virus. Finally, the Sabin vaccine is at least ten times cheaper than the Salk type.

All this means that Sabin vaccine costs little, is easy to administer, immunizes swiftly, protects thoroughly, and provides "hear-immunity." It is for these reasons that Brazil changed from Salk to Sabin vaccine when the U.S. made the latter available. For these reasons the Soviet Union orally inoculated over 90 million people before the United States even licensed the vaccine. Ceylon, Japan, Czechoslovakia, and other nations have bought vaccines from both the U.S. and the U.S.S.R., and as Dr. Sabin testified before Congress, the "live" vs. "dead" dispute "has entered into the field of competition for favor in uncommitted nations." Now that United States production of Sabin type has begun, the under-developed countries will have every cause to prefer the oral vaccine to the Salk preparation.

While many doctors will continue to apply dead virus shots, the PHS noted that, despite the Salk campaign,...outbreaks and even some severe epidemics still occur.... [even] among individuals who have had 3 or 4 doses of the vaccine." Thus, even in the United States, the final end of polio may come only with the use of oral vaccine.

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