21. For years, researchers had believed that all SV40-contaminated Salk vaccine made between 1955 and 1963 had been used or discarded. 22. An estimated 90 million Americans received Salk vaccine injections and as many as 30 million were exposed to the virus. 23. In short, the Internet has been a combination of the hydrogen bomb, the Salk vaccine for polio and Mother Teresa. 24. In this country, the Salk vaccine soon ended the yearly threat of epidemics and the toll of paralysis and death. 25. The introduction of the Salk vaccine in the 1950s and the Sabin vaccine in 1961 brought hope of controlling the virus. 26. In the end, even Salk's doubters concede that they don't know exactly how the Salk vaccine will function in long-term testing. 27. Of the changes, the return last month of the Salk vaccine for polio, given by injection, has created the most controversy. 28. Because of this, the computer modem is way bigger than the Salk vaccine or even Olestra as far as I'm concerned. 29. Hattox said he contracted polio at 16 months of age, before the Salk vaccine that has made the disease a rarity. 30. Until 1955, when the Salk vaccine was introduced, polio was considered one of the most frightening public health problems in the world.
