The first type was developed by Jonas Salk and first tested in 1952. Announced to the world by Salk on April 12, 1955, it is an injection of inactivated (dead) poliovirus. The second type was an oral vaccine developed by Albert Sabin, using attenuated poliovirus. An attenuated virus is a much less harmful strain of the same virus. Human trials of Sabin's vaccine began in 1957 and it was licensed in 1962.
There is no long term carrier for poliovirus (carriers are people who carry the virus but have no symptoms of the disease), and polioviruses have no non-primate reservoir in nature. The virus cannot survive in the open environment for a long time. Therefore, interruption of person to person transmission of the virus by vaccination is the key step in removing polio entirely. The two vaccines have eliminated polio from most countries in the world. Polio worldwide has dropped from about 350,000 cases in 1988 to 1,652 cases in 2007.
References[change | change source]
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- "Wild Poliovirus Weekly Update". Global Polio Eradication Initiative. 2008-11-25. Archived from the original on 2008-06-16. Retrieved 2008-11-29. CS1 maint: discouraged parameter (link)