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Because most cases of polio are asymptomatic, the virus can circulate among a population for some time before it is known that there is polio in the community. While those who exhibit no symptoms may not be aware they are infected, they can still carry and transmit the virus to others, who may then develop symptoms themselves. If a person does develop some sort of symptoms, whether paralytic or not, then at least the period of contagion can be estimated; polio is generally most contagious in the ten days before and after symptoms occur. One in ever 200 polio infections results in a case of paralysis, so polio may circulate in the community for some time before it becomes apparent, for in abortive and non-paralytic cases of polio the patient is often presumed to just have the flu. Sadly, polio is usually not recognized as polio until a case of paralysis occurs.

The scourge of polio began to be put to an end in the 1950s with the development of the polio vaccine. Two vaccines were developed: one by Jonas Salk, perhaps the best-known vaccine, was made from an inactive polio virus and administered through injection, and then an oral vaccine was developed by Albert Sabin using a weakened form of the polio virus. Both of these vaccines became widely used as soon as they were developed, since they came right at the height of the polio outbreak of the 20th century. Because of these vaccines, polio has been nearly eradicated from today's industrialized countries. And, because of a push from the World Health Organization, polio is well on its way to being eradicated in other parts of the world.

Because of its lower cost, the oral Sabin vaccine is the one most commonly used in developing countries. This vaccine has had a tremendous positive effect in controlling polio outbreaks and stopping new ones from emerging in developing countries. When administered, it produces rapid intestinal immunity in a person (Murdin, Barreto, & Plotkin, 1996). Because of this, it is also the preferred vaccine for polio outbreaks. However, because the vaccine is made with a live virus, there is a danger of a paralytic polio infection developing from taking the vaccine, and there are, in fact, between 250 and 500 cases of this happening each year (James, 1995). Industrialized countries use the Salk vaccine, which provides individual protection against polio and is quite effective, though not as effective as the Sabin vaccine. However, because the Salk vaccine is made with a killed virus, there is no chance of a paralytic polio infection developing from being given it.

Polio has been with the human race for nearly its entire history. Ancient Egyptian hieroglyphs exist that depict the withered appearance of paralytic polio patients ("Polio," n.d.). While not a scourge for much of its history, this changed in the early 20th century, causing such widespread horror that vaccines were developed and quickly put into use. Because of their effectiveness and a worldwide push to eradicate polio, polio is well on its way to becoming a thing of the past.

Bibliography

Black, Katherine. (1996). In the Shadow of Polio: A Personal and Social

History. New York: Addison-Wesley.

James, Walene. (1995). Immunization: The Reality Behind the Myth.

New York: Bergin & Garvey.

Klein, Joel. (2005) Polio. Kids Health for Parents.

Iron Lung. (2005) Wikipedia.

Murdin AD, Barreto L, Plotkin S. (1996) Inactivated poliovirus vaccine:

past and present experience. Vaccine: 14:735-46

Polio. (n.d.) Polio.Com.