In February of this year, a case of polio was confirmed in a five-year-old child in Malawi and in the first days of March the same thing happened with another four-year-old child in Israel. Neither of them were vaccinated against this highly contagious disease caused by the polio virus. Although most poliovirus infections do not cause symptoms, five to ten people in every 100 may have flu-like symptoms.
In one in 200 cases, polio destroys parts of the nervous system, causing permanent paralysis in the legs or arms.
While not common, the virus can also attack the parts of the brain that help you breathe, which can lead to death. Five cases were recorded worldwide in 2021. For its part, the Pan American Health Organization (PAHO) called for increasing inoculation given that in 2020 the lowest percentage of children vaccinated with all three doses was recorded since 1994.
Israel had detected its last case of polio in 1989, while in 1991, 2002 and 2013 it had warned about the circulation of the virus but in the environment and in wastewater. In the case of Malawi, the last time the disease had been detected was in 1992. The World Health Organization (WHO) declared the eradication of polio in Africa in 2020 after waiting four years for the reappearance of a contagion in Nigeria .
Alejandro Castello, a research professor at the Immunology and Virology Laboratory of the National University of Quilmes (UNQ), maintains that the cases in Malawi and Israel are different because the first case is associated with the wild virus and the second is linked to the vaccine. . To stop polio in the wild, the oral attenuated vaccine also known as Sabin is necessary. “Now, if Sabin recombines with other viruses, it can regain virulence characteristics and generate a strain related to the vaccine. These cases occur when there are undervaccinated populations or overcrowding in certain places.” Therefore, in both cases it is very likely that vaccination deficits are what allow these viruses to circulate.
This news comes amid an alert issued by the WHO regarding immunization in Ukraine, where an outbreak of poliomyelitis was recorded in 2021, with two cases of paralysis and a total of 21 people in two provinces. In February of this year, a vaccination campaign aimed at boys and girls without the three doses began, but the Russian invasion stopped the measure.
The situation in America
The last confirmed case of polio on the continent was on August 23, 1991 in Peru. The disease affected Luis Fermín Tenorio Cortez, a three-year-old child who lived in Pichanaki, a town that is part of the Central Peruvian Jungle. Three years later, America was certified free of circulation of wild poliovirus.
Grenada was the first country on the continent to register its last case of polio in 1955. Argentina detected the last infection in 1984, Brazil in 1989 and Mexico in 1990. According to PAHO data, Venezuela has the lowest vaccination coverage against the virus . In 2019, only 62 percent of children completed their inoculation schedule. In contrast, Nicaragua and Saint Vincent and the Grenadines reported 100 percent of minors with the three doses against polio.
In February 2022, the agency asked countries in the region to make a greater effort to vaccinate children against polio. In 2020, immunization with the three doses was 82 percent and represented the lowest percentage since certification as a polio-free zone in 1994. “If vaccination coverage is not greater than 95% in each municipality and each community, the Polio can cause paralytic disease again and return to the region,” the agency warns.
How it is transmitted
Polio travels from person to person from the fecal matter of an infected individual, which reaches the mouth of another susceptible individual. Although in some cases the source of infection can be water or food contaminated with feces of infected people, it can also be transmitted through respiratory secretions. Given that a good part of infected people do not present symptoms, the hygiene measures necessary to prevent circulation may not be taken into account.
Although unvaccinated children under 15 years of age are more likely to acquire polio, the chances increase even more in children under five years of age. The risk of becoming infected increases when there are other unvaccinated people in the place where you live and hygiene conditions are poor. If you get sick, there is no antiviral or medication that will stop the progression of paralysis.
Importance of vaccination
“To limit the incidence of polio, the only way is to be fully vaccinated with all the doses necessary to stop the circulation of the wild virus,” says Castello. However, polio has an additional problem to the rest of the vaccine-preventable diseases. “Oral immunization, although it is very efficient in preventing infection by the wild virus, produces cases associated with the vaccine virus itself, which recombines with other similar viral agents that proliferate in the intestine and can produce a reversion to virulence.”
PAHO points out that two types of vaccines are used on the continent: the oral attenuated vaccine (OPV, also known as Sabin) and the injected inactivated vaccine (IPV, commonly known as Salk). The OPV vaccine contained all three types of poliovirus, 1, 2 and 3. Countries are slowly replacing the OPV vaccine with the IPV vaccine.
In the case of Argentina, immunization with OPV began in 1957 and, starting in 1971, increasingly massive operations were carried out. Since June 2020 – in a process that started in 2016 – the OPV was changed to the IPV. This vaccine is made up of three doses: the first at two months of age, the second at four and the third at six months. At five years of age, the only IPV reinforcement is applied when they enter primary school.
With this migration from the oral vaccine to the injectable vaccine in Argentina, Castello highlights that there is no longer a concrete possibility of having an associated vaccine case. "When you eradicated the circulation of the wild virus from your region, you can begin to migrate to the injectable vaccine because the Salk, by not producing immunity in the intestinal mucosa, would allow the wild virus to circulate because you do not have mucosal immunity."
Nicolás Retamar: Editor. Teacher and graduate in Social Communication.
