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Experimental Trials for the Salk Polio Vaccine

• Reference: Freedman, Pisani, and Purves, Statistics, Third Edition, W. H. Norton, 1998.

• The first polio epidemic struck the United States in 1916.

• Polio caused paralysis in hundreds of thousands of victims, especially children for forty years.

• Several polio vaccines had been developed by 1950; the one Jonas Salk developed was the most promising.

• Why not just give the vaccine to large numbers of children and see if the incidence of polio drops?

• What issues can you think of that complicate the situation?
  The number of polio cases dropped by half from 1952 to 1953 with no vaccine.

  Very few of the persons exposed to polio actually get the disease.

  Children from wealthy families are more likely to get polio than children from poor families. This is because childrem from poor families grew up in non-hygenic surroundings so they developed a partial immunity to polio.

  Some parents thought that the vaccine was dangerous and would not give their consent. Such parents were more likely to come from poor families than from wealthy ones.

  People that are vaccinated may behave differently than those who are not.

  The vaccine might have dangerous side effects that were not noticed in small scale trials. The vaccine can actually cause polio in some cases.

• Two clinical trials were conducted to test the effectiveness of the vaccine. One by the National Foundation for Infantile Paralysis (NFIP, otherwise known as the March of Dimes).

• Another study was conducted by Dr. Thomas Francis of the University of Michigan.

• Here are the results. The rate is polio cases per 100,000.

  	NFIP Study		Francis Study
  	Size	Rate	Size	Rate
  Treatment	225,000	25	200,000	28
  Control	725,000	54	200,000	71
  No Consent	125,000	44	350,000	46

• For the NFIP study, grades 1 and 3 were the control group, grade 2 was the treatment group; this study was neither randomized, nor double blind.

• For the Francis study, all children in grades 1, 2, and 3 were asked if they wanted to participate in the study. Of those whose parents gave consent, half were randomly assigned to the treatment group, the other half to the control group; this study was randomized and double-blind.

• Here are some additional references:
  Timeline Development of the Salk Polio Vaccine at the University of Pittsburgh

  "A Calculated Risk": The Salk Polio Vaccine Field Trials of 1954