Poliomyelitis: what it is, how it manifests itself and how it is prevented

Poliomyelitis: what it is, how it manifests itself and how it is prevented

1948. A team of researchers led by John Franklin Enders, at Children’s Hospital Boston, succeeds in successfully cultivating in the laboratory the human poliovirus. For this research, Enders himself, along with Thomas Huckle Weller and Frederick Chapman Robbins, received the Nobel Prize for Medicine in 1954. Then in a few years, we get to the vaccine. First the Salk, then the Sabin. Two effective vaccines. And the WHO reports that it is necessary to propose vaccination to those who are not protected. Even in Italy, after Italy was declared Polio-free in 2000, we talk about this infection again. And remember how vaccination is the most effective preventive tool we have at our disposal, in the face of a virus that has never been eradicated on the planet.

How the disease develops and what are the symptoms

The infection is caused by a particular virus, called poliovirus, which causes an acute infectious disease that can attack the nervous system. The virus in fact affects nerve cells and, in the most serious forms, can even induce a total paralysis. Poliovirus is extremely contagious: it can be transmitted through feces, therefore with contaminated water and vegetables, or even more easily through saliva or coughing.

It should be remembered that the virus can also lodge in subjects who are healthy carriers, therefore without any symptoms, as well as obviously in sick people. Once the virus has entered the body, it reproduces rapidly in the digestive system and from there it can reach the central nervous system. When it affects motor neurons it can result in paralysis. These phenomena can appear in a variable time between one and three weeks, since viral incubation is very variable.

Polio is often asymptomatic

It should also be said that the infection can go on without causing any problems in most people. And this, while it may seem strange, can be a problem. These subjects, while not having any signs of disease, can in fact become healthy carriers of the virus and pass it on in feces.

In about 4-8 percent of cases, however, the poliovirus infection is particularly subtle and resembles the picture of a normal flu. There are fever, sore throat, digestive symptoms such as nausea, vomiting and stomach pains. Generally the picture resolves itself in a few days, without the diagnosis of polio being reached. The most serious forms are instead characterized by the involvement of the nervous system: more or less in 3 percent of cases a form of meningitis develops linked to the passage of the virus in the central nervous system, which manifests itself with pain in the neck and back, vomiting, lethargy and sore test. Finally, the classic flaccid paralysis that was also seen in Italy in the 1950s, before the advent of the vaccine, is rarely observed.

Symptoms can last 2 to 3 days and there are different forms of infection: the most common is that which leads to paralysis affecting mainly the legs, but there may also be pictures with involvement of the cranial nerves (manifested for example with facial nerve palsy) or mixed forms. In short: the infection does not leave results in the most common forms, completely asymptomatic or flu-like. On the other hand, heavy aftermaths can manifest themselves for a few days or even become permanent: in the most serious forms, the infection can leave results that strongly penalize the ability to carry out normal movements.

How the vaccine defends us

In Italy, the last case of clinically detectable infection in a resident was registered in 1983, after a progressive decrease in the number of cases without any rise. We have therefore eradicated polio before other countries, considering that Europe became “polio free” in 2000.

The Sabin vaccine, certainly very valid for the type of response it produces, over time it has proved, albeit very rarely, to be able to induce cases of vaccine polio. In the meantime, research has made efforts to improve the Salk vaccine, which became available again in its revamped and safer version in the early 1990s. For this reason, the vaccine used for several years has been the Salk or IPV vaccine containing the three killed (inactivated) poliomyelitis viruses, administered by injection intramuscularly or subcutaneously. The complete course of polio vaccination involves the administration of 4 doses. A fifth dose is given to adolescents to impart lasting protection. The vaccine is available in single formulation or in combination with other vaccines.

The great Italian vaccination campaign

In our country polio it caused about 3000 cases a year of severe disability and in 1958 there was a great epidemic with about 8500 people affected. The strategy that led to the campaign in 1964 took into account all children between 6 months and 14 years, because it was thought that above this threshold the population was immunized against the virus thanks to natural infection.

The Ministry of Health organized a great campaign with a formidable effort that involved all the national centers, also because the vaccine had to be stored frozen before administration. The campaign took place on three dates: in March he was vaccinated against Polio 1, in April for Polio 3 and in May for Polio 2. Protection against this strain was kept last, as it had proved less virulent. and above all it could interfere with the responses to other viruses. Finally, a booster was scheduled using a dose of trivalent vaccine.

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