Clarification on GPEI's Polio Eradication Strategy 2022-2026

Posted by Peter Bosch

How Do We Plan To Eradicate Polio?

The battle to eradicate Polio is complex and challenging, with changing tools and techniques, and a battlefield in constant flux. It is difficult to reduce it to an easily stated and understood set of goals. This article attempts to clarify the various timeframes and expectations in the recent Global Polio Eradication Initiative (GPEI) Strategy 2022-26.

What Do Those Goals Mean?

I have heard it said that Rotary expects that Polio will be eradicated by 2026, and while this was amended on 17 July by the Polio Oversight Board of the GPEI, I still want to offer some clarification. The following is based on discussions with Carol Pandak, the director of PolioPlus. Any inaccuracies, omissions, or misunderstandings are strictly and solely my own.
The Global Polio Eradication Initiative's (GPEI) Polio Eradication Strategy 2022-2026 has two main goals:
  1. Permanently interrupt all wild poliovirus transmission.
  2. Stop the transmission of poliovirus variants and prevent outbreaks.
The second goal might be easily misunderstood and is not expected to be fully achieved within the 2022-2026 timeframe. For a realistic view of the journey from "now" to "success," some clarification is needed.
 

Understanding Poliovirus Types and Vaccination

The wild poliovirus has three types: 1, 2, and 3. All three require vaccination. These types can occasionally reappear in areas where vaccination drives have been conducted because even attenuated live vaccines can mutate into virulence and be shed into the environment. This shedding can cause circulating vaccine-derived (also known as variant) poliovirus (cVDPV) types 1, 2, and 3 especially in unvaccinated people or those with compromised immune systems.

Surveillance and Reporting Improvements

Surveillance, analysis, and reporting are crucial. GPEI has an extensive network for environmental sampling, rapid testing, and symptom reporting around the world. This infrastructure will be a lasting legacy that benefits humanity even after polio is eradicated. Due to these advancements, the GPEI certification group now requires only two years without detection (instead of three) to declare a wild poliovirus eradicated and up to three years for variant poliovirus to be eradicated. The GPEI allows up to three years for cVDPV2 certification due to less robust surveillance in some outbreak countries compared to currently endemic countries. 

Eradication

Nominally two years after a wild and three years after a vaccine-derived poliovirus is last seen anywhere in the world and has not reappeared in outbreaks or environmental samples, it can be declared eradicated. Although wild poliovirus type 2 was eradicated in 1999, it still appears, vaccine-derived, in local outbreaks and must continue to be vaccinated against. Once the wild virus and its vaccine-derived variant are eradicated, we no longer need to vaccinate against it.
The Strategic Advisory Group of Experts on Immunization, which provides vaccine policy guidance to the World Health Organization, recommends 10 years of administering the inactivated poliovirus vaccine in routine immunization systems.

Established Vaccines

  1. IPV (Inactivated Poliovirus Vaccine):
    • Injectable vaccine that does not shed, thereby eliminating risk of derived poliovirus cases.
    • Expensive and requires extensive logistics, including refrigeration, and trained staff.
  2. OPV (Oral Poliovirus Vaccine):
    • The oral vaccine known for its use in mass immunization campaigns.
    • Inexpensive, durable, and effective, but can rarely mutate into a virulent form and shed into the environment, causing cases of vaccine-derived polio.

New Vaccine Tools

  1. bOPV (Bivalent Oral Poliovirus Vaccine):
    • Protects against poliovirus types 1 and 3.
  2. Monovalent OPV:
    • One vaccine specific to each of the three poliovirus types.
  3. nOPV2 (Novel Oral Poliovirus Vaccine):
    • Protects against type 2 with a very low rate of causing vaccine-derived polio.
 

So What Do GPEI’s 2022-2026 Goals Mean?

  • By the end of 2025: We expect the last detections (cases or environmental samples) of new wild polioviruses.
  • By the end of 2026: We expect the last detections of new cVDPV2 cases.
Therefore:
  • By the end of 2027: We aim to declare wild polio eradicated.
  • By the end of 2029: We aim to declare cVDPV2 eradicated.
    (The GPEI allows up to three years for cVDPV2 certification due to less robust surveillance in some outbreak countries compared to currently endemic countries.)
    • Post-cVDPV2 eradication: We will withdraw bOPV and nOPV2 from use and vaccinate tactically against type 1 or type 3 cVDPV outbreaks using the appropriate monovalent OPV rather than strategically against all three types of VDPV.
  • Remaining Task, post-2029: Eradication of cVDPV types 1 and 3 through tactically combating outbreaks. Monovalent novel vaccines, with higher efficacy and lower shedding, will be more effective in this stage than measures employed previously.
  • Challenges: Ensuring sufficient global stock of IPV (which does not shed) and monovalent novel oral polio vaccines (for both types 1 and 3) to combat specific outbreaks.
While no explicit decision has yet been made on the matter, Rotary International expects to remain engaged in the effort well past the 2026 timeframe.