Polio, or poliomyelitis, is a highly infectious viral disease that can cause paralysis and death. Thanks to widespread vaccination efforts, polio has been eliminated from most of the world. However, the poliovirus continues to circulate in a handful of countries, posing a threat to global eradication.
Where is polio endemic?
Currently, polio is endemic only in two countries – Pakistan and Afghanistan. This means that the wild poliovirus is circulating and causing new cases of polio paralysis. In 2020, Pakistan reported 84 new cases of polio while Afghanistan reported 56 new cases. These are the only two countries in the world where polio has never been stopped.
Several factors have allowed polio to persist in Pakistan and Afghanistan:
- Conflict and insecurity limit access to children for vaccination
- Mobile and remote populations can spread the virus
- Poor sanitation enables transmission of the virus
- Vaccine refusal and misinformation remain challenges
The vast majority of cases are concentrated in just a few areas of each country. In Pakistan, polio is entrenched in the northern tribal areas bordering Afghanistan. Meanwhile, Afghanistan’s polio reservoirs are in the southern region bordering Pakistan.
Where has polio been recently detected?
In addition to the endemic countries, there are several other areas that continue to see polio flare-ups:
- Africa: Polio outbreaks have occurred in recent years in countries such as Somalia, Nigeria, Niger, Congo, Central African Republic, Angola, Ethiopia, Kenya, Uganda, Mozambique and Malawi.
- Middle East: Israel, West Bank/Gaza, Syria and Egypt have all detected polio in environmental samples indicating circulation.
- Asia: Polioviruses have also been found in China, Philippines, Malaysia, Indonesia, Myanmar, Iran and Iraq.
These detections generally occur when the poliovirus is brought in from elsewhere and spreads in areas with low vaccination levels. They highlight the ongoing risk of international spread.
Which countries are vulnerable to polio?
Any country with suboptimal polio immunity levels is at risk for a potential outbreak. According to the Global Polio Eradication Initiative, the following countries and areas pose the greatest risk worldwide:
| Region | Countries/Areas of Concern |
|---|---|
| Africa | Chad, Guinea, Mali, Nigeria, Niger, Central African Republic, Democratic Republic of Congo, Ethiopia, Somalia, South Sudan |
| Middle East | Iraq, Syria, Yemen |
| Asia | Afghanistan, Pakistan, China, Philippines, Malaysia, Myanmar |
These vulnerable countries face challenges such as conflict, weak health systems, mobile populations, and vaccine hesitancy/refusal. Maintaining high immunity to polio requires repeated rounds of vaccination campaigns which can be difficult to implement in insecure areas.
Where has polio been eradicated?
Thanks to the Global Polio Eradication Initiative, polio has been eliminated from most of the world. Here is the status of the three wild poliovirus strains:
- WPV1: Last detected in Nigeria in 2016. Declared eradicated in 2020.
- WPV2: Last detected in India in 1999. Declared eradicated in 2015.
- WPV3: Last detected in Nigeria in 2012. Declared eradicated in 2019.
This means WPV2 and WPV3 no longer exist anywhere in the world. WPV1 continues to circulate in Pakistan and Afghanistan but has disappeared from the rest of the planet. Only vaccine-derived poliovirus circulates outside the endemic countries.
Some key regions certified as polio-free:
- Africa: Certified in 2020
- Europe: Certified in 2002
- South-East Asia: Certified in 2014
- Western Pacific: Certified in 2000
- The Americas: Certified in 1994
What progress has been made against polio?
The Global Polio Eradication Initiative has made tremendous gains against polio since it was launched in 1988:
- Cases have declined by over 99% from an estimated 350,000 in 1988 to 140 in 2020
- Wild poliovirus is now endemic in just 2 countries, down from 125 countries in 1988
- Independent regional commissions have certified 5 out of 6 WHO regions as polio-free
- 3 out of 3 wild poliovirus strains have been wiped out
- Over 19 million cases of paralysis have been averted
This represents one of the greatest public health achievements in history. Polio cases are at an all-time low and eradication is within reach.
How close is the world to eradicating polio?
We are currently in the polio endgame, with global eradication tantalizingly close but challenges remaining. Intense efforts are focused on the two remaining endemic countries, Pakistan and Afghanistan. The Polio Oversight Board has set targets for achieving zero cases, after which three years must pass without any detections to declare eradication. The current targets are:
- Stop polio transmission in Afghanistan by 2023
- Stop polio transmission in Pakistan by 2023
However, the COVID-19 pandemic has disrupted vaccination activities and surveillance, forcing the timeline to be pushed back already. Despite these setbacks, public health officials remain confident that polio eradication is achievable with sufficient political will, resources, and effort in the remaining endemic reservoirs.
What happens if polio is not eradicated?
Failure to eradicate polio could lead to a resurgence of the disease and tens of thousands of new cases every year. Modeling studies estimate 200,000 new cases annually in the next 10 years if eradication efforts cease. Polio-free countries would be continually at risk for imported outbreaks as well.
The enormous investments made so far could be jeopardized. The world would remain perpetually on the brink of the next outbreak, requiring expensive control measures. Ultimately, as long as polio exists anywhere, it remains a threat everywhere.
That’s why it’s critical to take advantage of the opportunity at hand while polio circulation is at an all-time low. The polio endgame strategy aims to simultaneously cut transmission in Pakistan and Afghanistan while strengthening defenses in high-risk countries.
What are the challenges to eradicating polio?
Reaching zero polio cases has proven incredibly difficult given the remaining challenges:
- Security: Conflict and inaccessibility hamper vaccination in key areas of Pakistan and Afghanistan.
- Complacency: As cases decline, commitment wanes in endemic and donor countries.
- Funding gaps: The program faces a major funding shortfall, threatening planned activities.
- COVID-19: The pandemic has disrupted vaccination campaigns and health services.
- Vaccine refusal: Mistrust and misinformation spark resistance, especially in Pakistan.
Overcoming these roadblocks at the very end has proven complicated. While Nigeria’s feat of interrupting polio shows it can be done even amid instability, the unique context in each endemic country necessitates tailored strategies.
What strategies are being used to eradicate polio?
Key strategies being used to wipe out the last vestiges of polio include:
- Intensified vaccination campaigns using the oral polio vaccine and, increasingly, the inactivated polio vaccine.
- Surveillance for poliovirus through testing sewage samples.
- Targeted approaches for high-risk mobile populations.
- Dialogue with local leaders and communities to build trust.
- Use of vaccination points at border crossings.
- Careful tracking of children missed during campaigns.
- Promoting basic sanitation and hygiene practices.
- Coordinated national and regional emergency action plans.
It will take a monumental effort, but public health officials believe polio eradication is achievable within the next few years using proven strategies if fully implemented.
Conclusion
The world finds itself on the brink of eliminating polio for good. While eradication has proven frustratingly difficult, we’ve never been closer thanks to dramatic progress over the last three decades. But the last mile is often the hardest part of any journey. Eliminating the final reservoirs in Pakistan and Afghanistan amid enormous challenges requires unrelenting commitment. The polio endgame calls for one final push to consign this crippling disease to the history books once and for all.