Wild polio virus strain 3 finally conquered say scientists

By Dr. Ananya Mandal, MDOct 26 2019

World Polio day is observed on the 24th of October. This year on the day officials announced that one of the three strains of the wild polio virus has been finally wiped out due to persistent vaccination efforts across the globe.

There are three wild polio virus strains (WPV strains) of which one is WPV3. Till date WPV2 strain had been eradicated before in 2015 and now the WPV3 joins the list leaving WPV1 still in circulation, explain the experts. This announcement was part of the independent Global Commission for the Certification of Poliomyelitis Eradication report by the World Health Organization (WHO). There has been relentless surveillance for the virus say the researchers before they came to this conclusion.

Polio virus, 3d illustration - Image Credit: nobeastsofierce / Shutterstock

The three strains were called Brunhilde, Lansing and Leon respectively in the 1950s with the first after a chimpanzee in a lab, second after Michigan city and the third after a boy from Los Angeles who died of it. These names were replaced by the current names of the strains WPV1, 2 and 3.

The last known case of WPV3 infection was recorded in Nigeria in 2012. Since then the only sample of the virus is in secure containment for recorded specimen preservation. Commission chair and vaccine expert David Salisbury declared at a celebration at WHO headquarters in Geneva, Switzerland, made the announcement saying, “Wild poliovirus type 3 is globally eradicated. This is a significant achievement that should reinvigorate the eradication process and provides motivation for the final step—the eradication of wild poliovirus type 1.”

According to experts, eradication of WPV1 could still be some way off and the strain was still in circulation in two known nations – Afghanistan and Pakistan. The WHO officials explain that the local issues including armed conflicted regions, misinformation regarding vaccine safety and fears regarding polio infections caused due to the vaccines itself are some of the hurdles. At present 88 children in Afghanistan and Pakistan suffer from polio paralysis.

Polio virus is a highly contagious virus that can spread via contaminated food and water through the feco-oral route and is thus a major health problem in regions with poor hygiene and sanitation. Children below five years are commonly affected and while many recover from the initial infection without any consequence, some may develop weakening of muscles and paralysis of the limbs. This paralysis may linger and turn permanent and lifelong. The paralysis often affects less than one in 200 children infected with the virus. At present there is no cure for the infection. Polio however can be prevented by vaccination.

Because of the large number of infected individuals remaining asymptomatic, surveillance of the viruses becomes an added challenge. Wide spread vaccination using oral polio vaccine can provide herd immunity to the whole population and prevent the spread of the infection. In the OPV (oral polio vaccine) strains of the weakened vaccine virus are administered and these remain within the guts of the vaccinated children and are excreted in their faeces. This weakened virus spread in regions with poor sanitation and overtake the spread of the WPV strains. Another form of vaccination against the infection is by Inactivated Polio vaccine or IPV that is administered as injections.

WHO Director-General Tedros Adhanom Ghebreyesus said in his statement this week, “The achievement of polio eradication will be a milestone for global health... We remain fully committed to ensuring that all necessary resources are made available to eradicate all poliovirus strains. We urge all our other stakeholders and partners to also stay the course until final success is achieved.” The WHO aims to eradicate polio by 2023.

Dr Matshidiso Moeti, the WHO's regional director for Africa, in his statement said, “The eradication of wild polio virus type 3 is a major milestone towards a polio-free world - but we cannot relax. Countries must strengthen routine immunisation to protect communities, ramp up routine surveillance so that we are able to detect even the slightest risk of polio re-emerging and ensure the timeliness and quality of outbreak response in the event that a case is detected.” Dr Moeti added, “This job is not finished until wild polio virus type 1 is globally eradicated, along with concerning outbreaks of circulating vaccine-derived polio virus.”

One of the major hurdles to polio eradication has been misinformation regarding the vaccines as well as fears regarding its safety. Oral polio vaccine has been associated with very rare cases of mutation of the weakened live viruses that may lead to vaccine-derived polio. Vaccine derived polio cases have been reported from 12 nations including Angola, Benin, Cameroon, Central African Republic, Chad, Democratic Republic of the Congo, Ethiopia, Ghana, Niger, Nigeria, Togo and Zambia, in alphabetical order. There are a total of 95 reported cases of vaccine derived infections in Asia and Africa say reports.

Michel Zaffran, director of polio eradication at the WHO said that despite the fact that only WPV1 remains, the vaccines available are not monovalent or specific against WPV1 only. “The Type 2 was so powerful that it dominated the old vaccine,” he said. “Removing Type 3 will not make the current one more immunogenic.” Dr. Ananda S. Bandyopadhyay, a polio program officer at the foundation said that their teams are working on the genetics of the weakened viral strains to prevent its mutations to cause vaccine-derived polio. He said that a new vaccine strain was on its way and could be ready by next year.