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On July 21, the New York State Department of Health announced to have detected a case of poliomyelitis in Rockland County, which is part of the New York metropolitan area, in the United States. This infectious disease was not reported in the United States for nine years: it would be a person who has contracted a strain of poliovirus resulting from the oral vaccine probably in a foreign country. The authorities instruct health workers to monitor the situation e recommend polio vaccination: the subjects most at risk, in fact, are people who have not been vaccinated and those who have not completed the vaccination cycle.
One disease, two vaccines
It was 2013 when the Centers for disease control and prevention (CDC) detected the last – non-native – case of polio in the United States (but since 1979 there have been no natural cases recorded in the American territory): since then, for as many as nine years, there have been no new infections of this viral diseasecaused by three different strains of poliovirus, a type of virus that is transmitted through the ingestion of contaminated food or with the direct contact among infected people. Symptoms are usually mild and flu-like (such as tiredness, fever, headache, stiffness, muscle pain, vomiting), but in some cases poliomyelitis can lead to paralysis or be fatal. Once present in the intestine of the infected person, in fact, the poliovirus invades the cells of his nervous system in a short time, causing the permanent damage to neurons And irreversible paralysis, including to the muscles involved in breathing, which can ultimately lead to death. There are no specific treatments for polio: if during the twentieth century the disease was eradicated in many countries of the world (in Italy the last case dates back to 1982) it is thanks toaction of vaccines.
In particular, two different types of polio vaccines have been developed: the first is a inactivated virus vaccine (also known by the acronym Ipv), created by Jonas Salk in 1955, administered through an intramuscular injection And consisting of poliovirus strains killed with formalin. A few years later, in 1961, Albert Sabin developed the attenuated virus vaccine (Opv), administered by the route oral (during the massive immunization campaigns of the last century it was dissolved on a sugar cube) and consisted of live poliovirus strains, treated in such a way that they lose the virulent characteristics of wild strains but trigger a very similar immune response. In addition to activating the production of antibodies against the poliovirus in the blood, the vaccine Opv also stimulates a massive intestinal immune responsewhich, as stated in the site of the World Health Organization (WHO), would represent one of the reasons why mass vaccination campaigns with this vaccine would have been able to effectively block the transmission of wild poliovirus from person to person.
For these reasons Opv – as stated in the site of the Higher Institute of Health (ISS) – has made it possible to eradicate polio in Europe and is still recommended by the WHO to eradicate the disease globally. However, the fact that it contains live and non-attenuated poliovirus strains presents some critical aspects, such as the possible onset of so-called vaccine-derived polioviruses. According to the Cdcin fact, a vaccine-derived poliovirus is a weakened viral strain at first included in the Opv vaccine and that, having changed over time, it has acquired characteristics that make it more similar to the wild poliovirus: this means that it can be transmitted more easily to unvaccinated people and can cause the manifestation of the disease itself, even with the most severe symptoms such as paralysis .
The US case
This is what would have happened for the new case of US polio: the CDC confirmed, through a gene sequencing performed in the laboratory, that the strain contracted by the person in the state of New York is a type 2 poliovirus derived from oral vaccine. Since the only polio vaccine used in the United States – since 2000 – is the IPV vaccine that cannot give rise to infectious polioviruses, health authorities speculate that the virus may have originated in a location outside the United States, where the Opv vaccine is still administered: one would have been created drive chain from an individual who received oral polio vaccine to one or more unvaccinated people, up to the New York case.
Since the polio vaccine is still part of the school immunization program in the United States, authorities reassure that children and people already vaccinated are at little risk. Instead unvaccinated people (including pregnant women) and those who have not completed the immunization cycle they should receive the IPV soonwhile people already vaccinated but exposed to the infection should undergo the booster dose.
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