Poliomyelitis: silent killer, which although preventable, spreads again after decades

Publicação: 10 de September de 2022

This year, samples of the virus have already been found in the sewers of New York and London. Israel and Malawi confirmed cases of the disease

Polio was already endemic in Brazil and the last reported case was in 1989. The disease-free country certificate was granted in 1994. The eradication took place thanks to intense vaccination campaigns

The reappearance of diseases hitherto controlled due to lack of immunization is a ghost that haunts countries that record a constant drop in vaccination coverage. A report by the World Health Organization (WHO) shows that global immunization coverage, including polio, fell from 86% in 2019 to 81% in 2021. Although preventable, this deadly disease, which used to paralyze tens of thousands of children every year, has once again spread after decades. Of the three wild poliovirus strains (type 1, 2 and 3), wild poliovirus type 2 was eradicated in 1999 and no type 3 cases have been found since the last report in Nigeria in November 2012. Meanwhile, the maintenance of type 1 circulation in 2020 in two countries, Pakistan and Afghanistan, has again caused concern. Despite the enormous difficulties, countries have advanced in their vaccination programs and achieved a significant reduction. The number of cases and transmission of wild poliovirus in these countries is currently at its lowest level in history, but nevertheless reveals the imminence of reintroduction of the poliovirus in countries where the disease has already been eradicated. About one in every 200 infections leads to irreversible paralysis and, among these patients, up to 10% die.

Dr. Dorcas Lamounier Costa, an epidemiologist, tropicalist physician and full professor in the area of Pediatrics at the Federal University of Piauí (UFPI), considers that another major concern, however, is related to cases of polio associated with vaccine-derived poliovirus (VDPV). The WHO has been following the surveillance of poliovirus in environmental samples and also cases of VDPV-associated polio and recently samples of the virus have been found in the sewers of New York and London. The case in the United States, on July 21, it happened almost a decade after the last known record of this highly contagious virus, which occurred in 2013. The infected person had not been vaccinated against the disease. After the notification of the poliovirus positive sample, local health authorities initiated a public health investigation and response. For Dr. Costa, polio eradication strategies are effective when fully implemented. “This was demonstrated by India’s success in stopping the circulation of the poliovirus in January 2011, in a technically challenging scenario. The territory of Southeast Asia received WHO certification as a polio-free region in 2014. Thus, it is clear that the imminence of reintroduction of the polio virus in a region declared free of circulation and the maintenance of high vaccination coverage, even in regions where the disease is eradicated is of fundamental importance,” stresses Dr. Costa. Also according to her, epidemiological surveillance should be active and sensitive to quickly detect typical or atypical cases and implement control actions. “This is why, even without disease since 1989, Brazil maintains the recommendation of compulsory notification of cases of flaccid paralysis, which most likely will not be poliomyelitis. It is necessary to know that no case of flaccid paralysis was due to poliovirus infection,” she adds.

Poliovirus poses a risk to unvaccinated people

The low vaccination coverage in Brazil is worrisome. Unfortunately, the inactivated polio vaccine, which was introduced in 2012, completes 10 years with a decrease in vaccination coverage for at least seven years. According to data from the Information System of the National Immunization Program (SI-PNI), only 47% of children aged one year received the three doses of inactivated polio vaccine. The percentage has not reached the 95% desired by the Ministry of Health since 2015. Last year, it reached only 70% of children. “The Pan American Health Organization (PAHO) has placed Brazil and seven other Latin American countries as high-risk areas for the return of polio. The alert occurs in the same year that Jerusalem, Israel, detected cases of the disease, Malawi, in Africa, again registered a case of wild poliovirus, and the city of New York, in the United States, notified a case of poliomyelitis with paralysis, by strain derived from the vaccine virus, in an adult who had not traveled abroad. In London, UK, the isolation of vaccine-derived poliovirus type 2 (VDPV2) from environmental samples was confirmed, in this case the virus was isolated only from environmental samples – no case of paralysis was detected. These isolated events, scattered around the world, oblige us to reflect on the importance of prevention actions at the world level,” argues Dr. Costa.

In the United States, unvaccinated people remain at risk for paralytic poliomyelitis if they are exposed to wild-type poliovirus (serotype 2) or vaccine-derivative. Thus, the country is stimulating and investing in vaccination campaigns. Sustained transmission of the poliovirus has been eliminated in the United States for approximately 40 years. The situation is also worrying in London, which has one of the worst vaccination rates in the country, with about a third of children not receiving the first vaccine at 12 months of age and almost a quarter missing another dose at 24 months. After the identification of the poliovirus in the sewers, children living in the British capital will receive an extra dose of the vaccine. According to the UK Joint Committee on Vaccination and Immunization, the booster dose of the inactivated vaccine will be given to children aged 1 to 9 years in all London neighborhoods.

The Professor of Medicine at the Federal University of São Carlos (UFSCar), director of the Oswaldo Cruz Foundation (Fiocruz) and leader of the Genomic Surveillance of the Public Health Disaster Preparedness and Response Unit of PAHO/WHO, Dr. Rodrigo Stabeli, recalls that in Brazil, the last recorded case was in 1989, and in 1994, the country received the certification of eradication of autochthonous poliovirus transmission. “This is all thanks to the live attenuated virus vaccine, which is administered orally,” he adds. In addition to the droplet, there is also the version of (vaccine with) dead, inactive virus, whose application is intramuscular. In terms of effectiveness, both are effective against the three polio serotypes. Asked if when passing from one person to another, the virus can mutate or cause paralysis, Dr. Stabeli explains that the attenuated vaccine, which is administered in the first year of life of babies, does not have the power to infect people, but the live virus contained therein replicates in the intestinal tract and can contaminate the environment and, consequently, people, orally. “The live attenuated virus that can be expelled in feces can circulate in a subpopulation that is under vaccinated or in immunocompromised individuals. In this population it can cause severe illness and paralysis. But in a population with a high vaccination rate, vaccine-derived poliovirus is not a concern. However, if vaccination rates begin to drop, the virus may under-circulate. That is, a country with massive effectiveness of the vaccine, there is no risk of an outbreak of polio derived from the vaccine virus,” he says.

However, it can happen, although rarely, that this attenuated virus reverts to the virulent state. If the person has received the three doses in the first year of life, they will be immune and will not become infected (or, if infected, will not get sick). In very rare situations, immunocompromised people can become infected with the vaccine virus and develop the disease. This is why children with AIDS or other diseases that compromise immunity should not receive the oral (attenuated) polio vaccine. “Viral poliomyelitis derived from the vaccine occurs due to genetic instability of the vaccine virus or by combining the genetic material of the vaccine virus with other viruses that live in the intestine, causing the emergence of mutant, more aggressive viruses capable of causing poliomyelitis and being transmitted to other people. Since the first notification of an outbreak caused by VDPV, no cases have been identified in Brazil,” he says.

With new technologies available, would the polio vaccine be outdated? Dr. Stabeli is categorical in stating that the oral vaccine (Sabin) is not outdated. In his opinion, it, besides being effective, is the major protagonist of the eradication of polio in the world. As for the types of vaccines against the disease, the professor emphasizes that one does not replace the other. “Droplet and intramuscular vaccines are complementary from the point of view of the immunization policy and strategy that can be exercised in the country. The droplet vaccine, for example, as it is easy to apply, allows a massive vaccination campaign, its objective is this,” he stresses. Finally, Dr. Stabeli points out that the way it is presented and administered in Brazil does not pose a risk to the population due to important vaccination coverage. “Even when we were acquiring this coverage, we did not have episodes of childhood paralysis caused by reversal of the vaccine virus, but by the circulation of serotype type 2,” concludes Dr. Stabeli.

The spread of the poliovirus poses a risk to non-immunized people and to remove this threat, which terrified parents around the world during the first half of the twentieth century, the path is vaccination. The vaccine provides almost 100% protection to fully immunized people. Since 2016, the vaccination scheme available in Brazilian basic units provides for three doses of the inactivated vaccine (IPV), applied in the second, fourth and sixth months of life of the child. The booster dose should be given in the 15th month and then at 4 years of age. In these cases, by oral vaccine (OPV). “Any and all polioviruses, wild or vaccine-derived, anywhere will always be a threat to children and other vulnerable populations everywhere. It is essential that the Polio Eradication Strategy GPEI 2022-2026 is implemented in all countries to ensure a polio-free world,” points out Dr. Costa. The fight against polio is considered an international health emergency by the WHO.

It is worth remembering that 10/24 is the World Day to Combat Polio and that vaccination is the only way to prevent the disease.

Post-Polio Syndrome

Many who suffered from polio as children spend years without any complaints. But the disease can return in the form of Post-polio Syndrome (PPS). According to Dr. Costa, the syndrome, unlike the primary infection by the polio virus, affects previously infected people, who have already recovered from paralytic polio. “These people may have new symptoms of weakness, muscle fatigue, general fatigue and pain. The physical symptoms of PPS can be severe enough to decrease an individual’s quality of life, significantly alter work function, and impose lifestyle changes. The psychological implications of once again facing a disease that had stabilized can be devastating,” she regrets. Also according to the pediatrician, the criteria for the diagnosis are a history of paralytic poliomyelitis with partial or complete recovery of neurological function followed by a period of stability (usually several decades), new persistent muscle weakness or abnormal muscle fatigue, provided that other causes have been excluded. PPS occurs in approximately one third of individuals with a past history of previous poliomyelitis, who have already recovered partially or completely. In Germany alone, approximately 70,000 people are affected. After about 40 years, they develop the typical symptoms of the disease, such as paralysis.

About Polio

Poliomyelitis, also called polio or childhood paralysis, is an infectious viral disease that mainly affects young children. Transmission occurs by direct person-to-person contact, by the fecal-oral route (most often), by objects, food and water contaminated with feces of patients or carriers, or by the oral-oral route, through droplets of oropharyngeal secretions (when speaking, coughing or sneezing). Lack of sanitation, poor housing conditions and poor personal hygiene favor transmission. Poliovirus multiplies in the intestine and then can reach the central nervous system leading to meningitis, meningoencephalitis, encephalomyelitis. About 60% of infected people develop the paralytic form with varying degrees of impairment. In severe cases, in which muscle paralysis occurs, the lower limbs are the most affected.

The most common symptoms are fever, malaise, head, throat and body pain, vomiting, diarrhea, constipation, spasms, stiff neck and even meningitis. In the most severe forms, muscle flaccidity is installed, which affects, as a rule, one of the lower limbs. There is no specific treatment, all contagion victims should be hospitalized, receiving treatment of symptoms, according to the patient’s clinical condition.

The sequelae are related to infection of the spinal cord and brain by poliovirus, are usually motor and have no cure. The main ones include problems and pains in the joints; clubfoot, known as equine foot, in which the person cannot walk because the heel does not touch the floor; different growth of the legs, which causes the person to limp and lean to one side, causing scoliosis; osteoporosis; paralysis of one of the legs; paralysis of the speech and swallowing muscles, which causes accumulation of secretions in the mouth and throat; difficulty in speaking; muscle atrophy; hypersensitivity to touch. The sequelae are treated with  physiotherapy, by performing exercises that help to develop the strength of the affected muscles, in addition to helping in posture, thus improving the quality of life and reducing the effects of sequelae. In addition, the use of medications to relieve muscle and joint pain may be indicated.