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On the famous photograph that immortalized the Yalta agreements, in February 1945, Stalin, Churchill and Roosevelt are sitting on a bench, a little dynamic posture for personalities who come to take important decisions for the future of Europe. But there is a good reason: Roosevelt is paralysed in both legs. It cannot stand alone, and a disabled person cannot represent the world's power. It is in 1921, at the age of thirty-nine years, the Roosevelt was reached by what diagnosed as poliomyelitis (but who in fact proved to be a rare neuromuscular disease). Its financial and political support will be crucial in the development of two vaccines against polio still used today.

Atrophy of muscles

Now that polio has disappeared from developed countries, it is difficult to imagine the media event that was, on April 12, 1955, the announcement that the vaccine developed by Jonas Salk was effective. It must be remembered that in the most severe epidemics, as that of 1952, were recorded up to mental new cases, including 3,000 died and some 21.300 retained sequelae of paralysis.

Since 1908, known polio of viral origin, but must await the end of the 1930s that we find the mode of contamination. The polio virus enters the body through the mouth and multiplies in the intestine, from which it spreads throughout the body. Is it enters the central nervous system-1 à 2-, he is destroyed responsible mobility neurons, resulting in paralysis, and muscles atrophy. But most of those infected, there is only an atypical infectious episode, or even no symptoms, and after to be multiplied in the intestine, the virus are excreted and can then be transmitted to other individuals.

The first available vaccine, Jonas Salk, is based on inactivated virus, i.e. death. Injectable, it triggers the production of antibodies in the blood, but not immunizes the intestine. If the vaccinated individual is protected, on the other hand, the cycle of transmission of the virus is not interrupted. It is a second vaccine, oral, and developed by Albert Sabin, who succeed. This doctor uses, not fragments of virus inactivated as Jonas Salk, but attenuated live virus, i.e. having lost its virulence. He is still able to infect the body, but not the central nervous system and therefore causes paralysis. Closely mimicking the real infection, it triggers an immune response identical to the one caused by a real virus. Finally, as in natural infection, after a few weeks, attenuated virus is totally eliminated from the body by excretion.

The benefits of this vaccine quickly have the tool of choice against the disease. If, in Europe, continued to use the injectable vaccine, it produced more than the oral vaccine in the United States, at the end of the 1960s. And who, building on its success in the eradication of smallpox, committed in 1988 in the same operation for polio, using oral vaccine. With some success. Currently, America, Europe, and Western Pacific areas are declared "liberated polio." But in Asia and Africa, residual outbreaks of the disease persist. Local conflicts hinder systematic immunization campaigns, when this is not the refusal of certain subgroups of people for religious reasons.

Full substitution

But another problem, linked to the vaccine itself, also made its appearance. The repeated passage of the attenuated virus from one individual to the other multiplies its opportunities to deploy, so become virulent. Five cases of paralysis associated with oral polio vaccine-derived poliovirus strains have thus been listed during the winter of 2001-2002 in Madagascar. Aware of the problem, who therefore recommended in May 2008 to stop the use of the oral Sabin Vaccine as soon as possible after detection of the last natural case of polio. However, a full substitution of the injectable vaccine would not be without problems, both in terms of production capacity and mode of administration, with the risk of harming the overall coverage. Thus, the prospects for a total eradication of polio away, making the pursuit of immunization in areas liberated from the disease, more necessary than ever because of population movements.

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