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- The history of Polio – from eradication to re-emergence
September 2022
Deformed or paralyzed legs. Atrophied torsos and trouble breathing. For children left crippled with paralysis, a lifetime of disability and pain. This was the fate of thousands who survived the virus known today as polio. This disease, poliomyelitis, was previously known as “infant paralysis,” and affected humanity throughout history.
When the Pan American Health Organization (PAHO) was created in 1902, the highly contagious nature of polio would not be discovered by the medical community until 1905. Eventually, with the development of the vaccine and tireless immunization efforts supported by PAHO, in 1994 the Region of the Americas became the first one in the world to be certified polio-free by the World Health Organization (WHO).
Polio is the short name for poliomyelitis, a highly infectious disease caused by the poliovirus. There are three wild types of polioviruses, types 1, 2, and 3, and only two countries where the wild poliovirus type 1 is still endemic: Afghanistan and Pakistan.
Recently the disease made headlines again when a case was detected in the United States in July 2022: an unvaccinated 20-year-old man was diagnosed with a type known as “vaccine-derived poliovirus (VDPV).” This is a strain related to the weakened live virus contained in the oral polio vaccine (OPV).
According to Dr. Gloria Rey, a polio expert and Regional Advisor at PAHO, if the weakened live poliovirus can circulate in populations with low vaccination coverage, it can mutate and revert to a form that causes illness and paralysis. This highlights the importance of maintaining high vaccine coverage across all countries.
Among the unvaccinated, the virus attacks the nervous system and can cause total paralysis in a matter of hours. It is transmitted through contact between people, via nasal and oral secretions, although more commonly through contact with contaminated feces.
The initial symptoms are fever, fatigue, headache, vomiting, stiffness of the neck and pain in the limbs. One in 200 infections lead to irreversible paralysis (usually in the legs). Among those paralysed, 5 to 10 percent die when their breathing muscles become immobilized.
During the height of the regional polio epidemic in the 1950s, a machine known as an 'iron lung' was usedto aid patients whose muscles had weakened. Although this machine alleviated breathing, it was no cure, and the race was on to find a vaccine.
Life protection through vaccination
It was in 1955 that Jonas Salk’s injectable vaccine was announced safe to use and a nation-wide immunization campaign began in the United States. Salk’s vaccine is called “an inactivated polio vaccine” (IPV), meaning it uses a polio virus that is not alive.
In 1962, an oral polio vaccine (OPV) was developed by researcher Albert Sabin, using an attenuated – or weakened – live polio virus. As his vaccine was easier to administer, it greatly facilitated distribution. Today both vaccines are used.
Dr. Rey said that, at this time, the recommendation of the Technical Advisory Group (TAG) on Immunizations is to use both the injected and oral vaccines to generate optimal immunity.
As part of the primary vaccination schedule during the first year of life, a baby should receive two doses of the injectable vaccine (IPV) and one dose of the oral polio vaccine (OPV), as well as two boosters at 18 months and 5 years old. This scheme provides life-long protection.
A global milestone
Following the Sabin vaccine discovery, the eradication of polio from the Americas was a matter of time. In the 1980s, PAHO, led at the time by Dr. Ciro de Quadros, began to mobilize support from health authorities to make the eradication of this ancient disease a reality.
In 1994, after the concerted efforts of thousands of health workers, vaccinators, epidemiologists and the immunization team at PAHO, the Region of the Americas was the first in the world to be certified polio-free by the WHO.
On August 23, 1991, Luis Fermin Tenorio Cortez, a child in Peru, was the last person to suffer poliomyelitis in the Americas when he was infected with wild poliovirus in the District of Pichinaki, in the Province of Chanchamayo, in the remote mountains of the Junín Department, nearly 400 kms from Lima.
Identifying the last case of polio in the Americas was a major milestone, involving the input of scientists and independent experts who were part of the International Commission for the Certification of Polio Eradication.
Renewed call for immunization
The early detection of cases through robust surveillance of acute flaccid paralysis (AFP) in children under 15 years of age and high vaccination coverage were key to keeping the Americas free of polio for decades.
The 2022 detection of the vaccine-derived polio case in New York, however, raised the alarm among public health authorities across the world, and a renewed call to improve immunization rates.
“Polio vaccination coverage in the region is at 79 percent, the lowest since 1994,” Dr. Rey warned. Many factors explain the decline, including vaccine hesitancy and, more recently, the COVID-19 pandemic.
The recommended vaccination coverage to prevent the reintroduction of the virus is 95 percent. In 2020, only 80 percent of children had received the third dose of the oral vaccine needed for full immunization – a decline from 87 percent in 2019.
“When vaccination levels are low, the unvaccinated in a community are more susceptible to the disease, increasing the likelihood that the weakened poliovirus mutates and reverts to a strain that is able to infect and cause paralysis,” Dr. Rey added.
“The key to eradication is to keep up vaccination rates and to improve communication. Also, to incorporate the threat of re-emergence in the medical curriculum for young doctors and medical professionals both in urban and remote, vulnerable areas,” said Dr. Roger Zapata, a paediatrician in Lima, who detected Tenorio Cortez’s case of polio over 30 years ago.
In 2019, Peru held a nationwide campaign to improve vaccination coverage, including measles, rubella and polio. When the pandemic hit in 2020, many clinics were repurposed to deal with the high influx of COVID-19 patients, leaving many children unvaccinated.
“Today, there is a real risk of the re-introduction of polio in Peru,” said Dr. Ivy Lorena Talavera, an international advisor on Family, Health Promotion and Course of Life at PAHO.
Low vaccination rates, limited surveillance of acute flaccid paralysis, coupled with stretched human resources can contribute to a high risk of polio reintroduction not just in Peru, but across the region, she explained.
“Nobody wants a return scenario to the iron lungs of the1950s,” Dr. Rey said. “We need to do our best effort to vaccinate children and reach more than 95 percent vaccination coverage to guarantee that our region remains polio-free.”
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