Wild polio virus type 3 (WPV3) has been eradicated worldwide, the World Health Organization declared Thursday following a review of the global data by an independent commission of experts. The announcement about WPV3, coinciding with World Polio Day, comes after wild polio virus type 2 (WPV2) was declared eradicated in 2015.  Although one other wild virus strain, as well as vaccine derived infections, still persist, the announcement brings polio one important step closer to eradication. That would make polio the second human disease to disappear from the planet, following smallpox, which was eradicated in 1980.

The last case of WPV3 was detected in Yobe, northern Nigeria in 2012. Seven years later, after no new cases of WPV3 were detected by the Global Polio Eradication Iniative’s (GPEI) global surveillance system, an official certificate of global WPV3 eradication was presented to the World Health Organization by the Global Commission for the Certification of Poliomyelitis Eradication, the independent body of experts responsible for certifying polio eradication.

“Today we’re celebrating another milestone on the road to a post-polio world – the eradication of wild polio virus type 3…But this is only a milestone – we have not reached our destination. The last mile, as we all know, is the hardest mile [to reach] and we must continue with greater dedication until polio is finally eradicated,” said Dr Tedros Adhanom Ghebreyesus, director-general of the WHO and chair of GPEI’s Polio Oversight Board, at Thursday’s event announcing the global eradication of WPV3.

In addition, no cases of wild polio virus type 1 (WPV1), the only wild-type strain still circulating, have been detected in Africa since 2016, also setting the WHO African Region on track to be certified for eradication of all wild types of polio virus in 2020. The WHO European region, the Americas and Southeast Asia eradicated all three strains of wild polio virus some years ago.

Still, WPV1 circulation in Pakistan and Afghanistan, and new cases of vaccine-derived polio virus remain barriers to global eradication. Despite differences at the genetic level, all the different strains of polio can cause paralysis or death – making the eradication of these last two types crucial to completely erasing the threat of polio.

WHO hopes that the announcement of the eradication of WPV3 will spur a renewed commitment to the global polio eradication campaign, led by the public-private partnership GPEI, which consists of WHO, Rotary International, the US Centers for Disease Control and Prevention (CDC), the United Nations Children’s Fund (UNICEF) and the Bill & Melinda Gates Foundation. Donors and leaders in global health will announce new commitments to the GPEI’s Endgame Strategy 2021-2023 at the Reaching the Last Mile Forum on November 19^th in Abu Dhabi, United Arab Emirates, which will convene under the theme “Accelerating the Pace.”

The Last Threats: Wild Polio Virus Type I (WPV1) and Vaccine-Derived Polio Virus (VDPV)

Now, there is only one strain of wild polio virus (type 1) circulating in pockets of Afghanistan and Pakistan – where insecurity and community mistrust hinder the eradication campaign. Pakistan in particular has seen an upsurge in cases with over 70 reported so far this year.

In addition, cases of vaccine-derived polio virus (VDPV), reported mainly in Africa, remain a threat to the eradication campaign. VDPV is caused by a mutated strain of the weakened virus found in the oral polio vaccine – when a population is underimmunized against wild polio virus, VDPV can circulate in the community until it mutates to regain the ability to attack the nervous system. Therefore, achieving high consistent vaccination coverage is still the best way to prevent VDPV outbreaks, according to GPEI. Still, most VDPVs appear to be less transmissible than strains of wild polio virus, and outbreaks can cease on their own or with additional immunization activities.

To tackle VDPV, a group of immunization experts at WHO announced two weeks ago that they are conducting clinical trials on a new oral polio vaccine formulation (nOPV2) that could offer the same level of protection against polio while reducing the risk of VDPV. They are working with an Indonesian manufacturer to produce a batch of over 100 million doses of the new formulation, which could be rolled out as early as June of next year.

“We remain fully committed to ensuring that all necessary resources are made available to eradicate all polio virus strains. We urge all our other stakeholders and partners to also stay the course until final success is achieved,” said Dr Tedros in a press release.

Image Credits: UNICEF Ethiopia/Mulugeta Ayene 2018.