The WHO Regional Office for Africa, based in Brazzaville, Republic of the Congo, has confirmed the closure of poliovirus type 2 outbreaks in Burundi, Ghana, Guinea-Bissau, the Republic of the Congo and Uganda. The decision, announced on 19 August 2026, came after independent Outbreak Response Assessment (OBRA) teams found no evidence of continued transmission between January and June 2026. It marks a significant step in Africa’s long fight to end all forms of polio, even though only circulating vaccine-derived poliovirus type 2 (cVDPV2) was involved.
What is Polio and What is Poliovirus Type 2?
Polio, short for poliomyelitis, is a highly infectious viral disease that mainly affects children under five years of age. It is caused by the poliovirus, which belongs to the Enterovirus genus in the Picornaviridae family. The virus spreads mainly through the faecal-oral route, which means through contaminated water, food or hands, and it multiplies in the intestine before attacking the nervous system. In most cases infection causes no symptoms or mild fever, but in about 1 in 200 infections the virus destroys motor neurons in the spinal cord and causes irreversible paralysis, often in the legs, and in some cases death when breathing muscles are affected. The classic clinical sign used for surveillance is Acute Flaccid Paralysis (AFP), a sudden onset of floppy weakness in children.
There are three serotypes of poliovirus, called type 1, type 2 and type 3. Immunity to one type does not protect against the other two, so vaccines must cover each type separately. Wild poliovirus type 2 (WPV2) was last seen in India in 1999 and was declared globally eradicated in September 2015. Wild poliovirus type 3 (WPV3) was last detected in Nigeria in 2012 and declared eradicated in October 2019. Only wild poliovirus type 1 (WPV1) still circulates naturally, and it remains endemic in only two countries, Afghanistan and Pakistan. When polio is discussed today in Africa, it is almost never about wild poliovirus, since the WHO African Region was certified free of indigenous wild poliovirus on 25 August 2020.
Understanding Circulating Vaccine-Derived Poliovirus Type 2 (cVDPV2)
Most polio outbreaks in Africa today are caused not by wild virus but by circulating vaccine-derived poliovirus type 2, abbreviated as cVDPV2. To understand this, we need to understand how the oral polio vaccine (OPV) works. OPV contains a live but weakened form of the virus, known as Sabin strain, which replicates in the gut, builds strong intestinal immunity, and is excreted in stool. In well immunised communities, this excreted vaccine virus indirectly helps protect others. But in communities with low immunisation coverage and poor sanitation, the weakened virus can pass from one unvaccinated child to another for 12 to 18 months. During this chain of transmission it can slowly mutate, regain the ability to cause paralysis, and become a vaccine-derived poliovirus (VDPV).
When such a mutated virus is found in at least two different sources that are genetically linked, or in multiple children or environmental samples separated in place and time, it is classified as circulating VDPV (cVDPV). Because type 2 wild poliovirus has been eradicated, population immunity to type 2 is now the lowest, especially among children born after the global switch from trivalent OPV (tOPV) containing types 1, 2 and 3 to bivalent OPV (bOPV) containing only types 1 and 3 in April 2016. That immunity gap is the key reason why cVDPV2 accounts for about 86 percent of all circulating vaccine-derived outbreaks reported since 2000, with type 1 causing about 13 percent and type 3 only 1 percent. Like wild polio, cVDPV2 can cause paralysis, spreads silently through faeces and sewage, and is taken just as seriously as wild virus under the International Health Regulations (IHR). The solution, as with wild polio, is the same, high coverage with polio vaccines to stop transmission.
How Does WHO Confirm That a Polio Outbreak is Closed?
An outbreak closure is not a political announcement. It is a country-specific technical determination that the virus strain linked to that particular outbreak has stopped circulating. It does not mean the country is permanently polio-free, and it does not protect against importation of a new virus from another country. Closure only means that, based on evidence, the chain of transmission that was declared as an outbreak has been interrupted.
In the WHO African Region, which covers 47 member states and is headquartered in Brazzaville, the authority to confirm closure rests with the WHO Regional Office for Africa after a formal independent review. The process is deliberately kept independent of the government that responded to the outbreak, so that the assessment remains objective.
The Independent Outbreak Response Assessment (OBRA) Process
The independent team that carries out the review is called the Outbreak Response Assessment (OBRA) team. It is convened under the Global Polio Eradication Initiative (GPEI), the global partnership launched in 1988 by WHO, Rotary International, the US Centers for Disease Control and Prevention (CDC), UNICEF, the Bill and Melinda Gates Foundation and Gavi, the Vaccine Alliance. An OBRA team usually has 5 to 8 external experts who were not involved in the outbreak response.
The teams in this instance conducted separate assessments for each of the five countries between January and June 2026. They reviewed three categories of evidence before concluding that transmission had been interrupted.
| Evidence Reviewed | What OBRA Checks |
|---|---|
| Disease Surveillance | Sensitivity of Acute Flaccid Paralysis (AFP) surveillance and environmental surveillance (ES) from sewage samples, including whether the non-polio AFP rate reached at least 3 per 100,000 children under 15 years in outbreak zones and whether at least 80 percent of AFP cases had adequate stool specimens collected within 14 days |
| Laboratory Data | Results from WHO-accredited polio laboratories and the Global Polio Laboratory Network of 145 laboratories, including intratypic differentiation and genetic sequencing to confirm no detection of the outbreak strain from any source for at least 12 months |
| Population Immunity and Campaign Quality | Coverage of supplemental immunisation campaigns, independent monitoring and Lot Quality Assurance Sampling (LQAS) results, routine immunisation coverage for OPV3 and IPV, and proof that high-risk, hard-to-reach and cross-border populations were reached |
According to GPEI Standard Operating Procedures, an outbreak can only be closed if no poliovirus of the outbreak serotype has been detected from any source, whether stool from AFP cases, contacts, healthy children or sewage, for at least 12 months after the last detection, plus an additional period to account for laboratory testing and reporting delays. Surveillance indicators must also have met quality thresholds throughout that period. Exceptionally, closure can be considered after 6 to 9 months without detection if campaign quality was very high and surveillance has been optimal for 12 months. After the OBRA field or desk review, the team presents its findings to national authorities and submits a report to the WHO Regional Office, which then makes the final technical decision to confirm closure. That is exactly what happened for the five countries in August 2026.
Five Countries Where Type 2 Outbreaks Have Been Closed
The five closures together represent different outbreak timelines, but all followed the same pattern, rapid detection, coordinated government leadership, support from GPEI partners, and years of sustained effort.
Burundi, Ghana, Republic of Congo, Uganda and Guinea-Bissau: Country-Wise Progress
Burundi declared a circulating vaccine-derived poliovirus type 2 outbreak in March 2023 after a case of acute flaccid paralysis in a four-year-old zero-dose child in Isale district, Bujumbura Rural, and five positive environmental samples from Bujumbura Mairie collected in November and December 2022. Sequencing linked the isolates to a new emergence first seen in South Kivu, Democratic Republic of the Congo. The Ministry of Health declared a national public health emergency, and with GPEI support intensified routine immunisation, expanded environmental surveillance to border areas, and carried out targeted vaccination campaigns for children under seven years, synchronised with neighbouring countries. OBRA confirmed interruption after more than two years without sustained transmission.
Republic of the Congo strengthened surveillance and ran multiple high-quality vaccination campaigns after initial virus detections in 2023. The last detection linked to this outbreak was reported in December 2023. Subsequent work focused on keeping surveillance sensitive and closing immunity gaps in high-risk areas, which convinced the OBRA team that circulation had stopped.
Uganda intensified disease surveillance and outbreak response after poliovirus related to the SOM-BAN-1 emergence was detected in May 2024. The strain had previously circulated in Somalia and Kenya and was the first time this lineage was found in Uganda. Authorities maintained strong coordination between national and subnational levels and maintained high-quality AFP and environmental surveillance for more than a year after the detection.
Ghana combined strong laboratory investment with rapid outbreak response. Along with Uganda, Ghana upgraded its laboratory capacity in early 2026, improving its ability to detect poliovirus and other vaccine-preventable diseases quickly. High-quality disease surveillance and rapid campaigns helped interrupt the cVDPV2 chain that had affected the country.
Guinea-Bissau showed the longest period without detection. After the Africa Regional Certification Commission certified Guinea-Bissau as free of wild poliovirus within the African Region’s certification in 2019, the country detected variant poliovirus type 2 in four samples in October 2021, three children with AFP and one contact in Bissau Autonomous Sector and Biombo region. The Ministry of Public Health declared a public health emergency on 21 March 2022 and conducted two rounds of supplementary immunisation with novel oral polio vaccine type 2 (nOPV2) from 27 to 30 April 2022 and 22 to 25 June 2022, reaching more than 600,000 children aged 0 to 59 months. Since July 2021 no poliovirus has been detected, and the OBRA review of population immunity, campaign coverage and surveillance concluded there was no evidence of continued transmission.
In all cases, the WHO statement stressed that closure must not lead to complacency. The recent re-detection of poliovirus in Madagascar after its previous outbreak had been closed shows how easily the virus can be re-imported across borders when surveillance weakens or immunisation coverage falls.
Why Vaccine-Derived Polio Emerges and How Vaccines Stop It
The paradox of vaccine-derived polio confuses many readers. If the vaccine causes the outbreak, why use it at all. The answer lies in coverage, sanitation and the type of vaccine used.
Oral Polio Vaccine, Inactivated Polio Vaccine and Novel OPV2
There are two main polio vaccines in use worldwide.
Oral Polio Vaccine (OPV) was developed by Albert Sabin in 1961. It contains live weakened virus and is given as drops in the mouth. It is cheap at less than $0.20 per dose, easy to give without a needle, and creates strong gut immunity that stops the virus from multiplying in the intestine. This gut immunity is why OPV can actually stop person to person spread. Different formulations exist, trivalent OPV (tOPV) with types 1, 2 and 3, bivalent OPV (bOPV) with types 1 and 3, and monovalent OPV (mOPV) with a single type. The drawback is the rare reversion to neurovirulence described earlier.
Inactivated Polio Vaccine (IPV) was developed by Jonas Salk in 1955. It contains killed virus and is given by injection. It creates excellent blood immunity that prevents paralysis but induces little intestinal immunity. That means a child protected by IPV will not become paralysed, but can still carry and spread poliovirus in the gut. IPV therefore cannot alone stop community transmission and IPV cannot cause vaccine-derived polio.
The risk of type 2 vaccine-derived outbreaks increased after April 2016, when the world withdrew the type 2 component from routine use. With low routine IPV coverage for type 2 and falling gut immunity, the niche for cVDPV2 expanded. Global cVDPV2 cases peaked in 2020 with 959 cases in 27 countries, 21 of them in the African Region, compared to 366 cases in 2019.
To break this cycle, scientists developed the novel oral polio vaccine type 2 (nOPV2). Development began in 2011, and nOPV2 became the first vaccine ever to receive WHO Emergency Use Listing (EUL) on 13 November 2020. It was fully licensed and WHO prequalified on 27 December 2023. nOPV2 is a modified version of mOPV2 with five targeted genetic changes that make the virus much more stable and about 80 percent less likely to revert and seed new cVDPV2 emergences, while keeping similar safety and immunogenicity. Between March 2021 and January 2024, about 1 billion doses of nOPV2 were administered in 35 countries, mostly in Africa. Guinea-Bissau used nOPV2 in its 2022 campaigns, and it is now the recommended vaccine for cVDPV2 outbreak response alongside bOPV and IPV in routine schedules.
| Vaccine | Contains | How It Protects | Risk of Vaccine-Derived Polio |
|---|---|---|---|
| bOPV | Live weakened types 1 and 3 | Humoral plus strong intestinal immunity, stops spread | No risk for type 2, very low risk for types 1 and 3 |
| mOPV2 / nOPV2 | Live weakened type 2, nOPV2 is genetically stabilised | Humoral plus intestinal immunity, stops spread of type 2 | mOPV2 can rarely seed cVDPV2, nOPV2 is about 80 percent less likely to do so |
| IPV | Killed types 1, 2 and 3 | Humoral immunity, prevents paralysis | Cannot cause cVDPV, cannot stop transmission alone |
High-quality campaigns using these vaccines are the only way outbreak response works. Independent monitoring thresholds for a quality campaign expect more than 90 percent of children marked as vaccinated, and Lot Quality Assurance Sampling (LQAS) pass thresholds above 90 percent. When coverage is high, population immunity rises enough to both stop the current outbreak and prevent a new vaccine-derived strain from taking hold.
Africa’s Larger Fight Against Polio: From Wild Poliovirus to Vaccine-Derived Strains
To appreciate the significance of these five closures, it helps to place them in Africa’s longer journey.
The Global Polio Eradication Initiative (GPEI) was launched in 1988 when the World Health Assembly resolved to eradicate polio. At that time, polio paralysed about 350,000 children every year in more than 125 countries. Rotary International had launched its PolioPlus campaign in 1985, and together with WHO, UNICEF, CDC, the Gates Foundation and Gavi, built the largest public health partnership in history. More than 2.5 billion children have been immunised and more than 20 million volunteers have participated since then.
Africa’s path was especially hard. In the 1970s, lameness surveys revealed that an estimated 75,000 children were paralysed by polio each year in Africa, dispelling the myth that polio was a disease of affluent nations. In 1996, Nelson Mandela launched the Kick Polio Out of Africa campaign following the Yaoundé Declaration by African heads of state. The 270 million children immunised in synchronized National Immunization Days and the creation of the Global Polio Laboratory Network in 1990 with 145 laboratories steadily reduced cases.
Progress was uneven. Outbreaks in Nigeria, Angola and the Democratic Republic of the Congo repeatedly reseeded the continent. After Nigeria was removed from the endemic list in 2015, wild poliovirus was found again in insecure Borno State in 2016, linked to the Lake Chad Basin humanitarian crisis. A coordinated response across Cameroon, Central African Republic, Chad, Niger and Nigeria vaccinated 45 million children and helped the continent recover.
On 25 August 2020, the Africa Regional Certification Commission for Poliomyelitis Eradication (ARCC) declared the WHO African Region free of indigenous wild poliovirus. The last wild poliovirus case in Africa was in Borno, Nigeria on 21 August 2016. The region became the fifth of six WHO regions to achieve this status, after the Americas (1994), Western Pacific (2000), Europe (2002) and South-East Asia (2014). Only the Eastern Mediterranean Region, where WPV1 remains endemic, is yet to be certified.
But certification did not end polio in Africa. Since 2017, more than 15 African countries have reported cVDPV2 outbreaks. In 2022 alone, more than 400 cVDPV2 cases were reported in 14 African countries. In Malawi and Mozambique, an imported wild poliovirus type 1 strain from Pakistan caused nine cases in 2022 and was only closed after more than 50 million children were vaccinated in five southern African countries. The current five closures show that while wild poliovirus has been eliminated from Africa, vaccine-derived strains remain the main challenge and require the same rigour in surveillance and vaccination.
What Remains to be Done to Keep Africa Polio-Free?
WHO Regional Director for Africa Dr Mohamed Janabi captured the message when he said that the closures show what strong national leadership, dedicated health workers and close collaboration with communities and partners can achieve, but that continued vigilance and high immunisation coverage remain essential.
Outbreak closure does not equal zero risk. The virus can be imported from neighbouring countries where cVDPV2 still circulates, especially in areas with large population movements, weak routine immunisation, or conflict and displacement. That is why the OBRA reports for all five countries include detailed technical recommendations.
The way forward includes maintaining high-quality AFP surveillance at a rate of at least 2 per 100,000 children under 15 years nationally and 3 per 100,000 in high-risk or outbreak areas, and keeping stool adequacy above 80 percent. It also means expanding environmental surveillance, the testing of sewage and wastewater, which can detect silent circulation even when no child shows paralysis. Ghana and Uganda both expanded laboratory capacity in early 2026 precisely for this reason.
Routine immunisation must also stay strong. Countries need to keep OPV3 and IPV coverage above 90 percent, conduct periodic outreach to chronically missed communities, and ensure that novel OPV2 is available in the global stockpile managed from Indonesia’s Bio Farma, currently the sole manufacturer. The Polio Endgame Strategy 2019 to 2023 and its successor plans lay out three pillars for a world free of all polioviruses, eradication through immunisation and surveillance, integration of polio functions into broader health systems, and containment of polioviruses in laboratories and vaccine facilities. Using polio resources to fight other diseases, from measles to Ebola, and registering births during campaigns, has already shown how eradication efforts can strengthen health systems as a whole.
For India, the relevance is direct. India reported its last wild poliovirus case in January 2011 in Howrah, West Bengal, and was certified free of wild poliovirus in March 2014 as part of the South-East Asia Region. It maintains a Pulse Polio programme and National Immunization Days with bOPV and IPV, and remains vigilant for importation and vaccine-derived strains. The African experience, from switching to nOPV2 to using independent OBRA verification, offers lessons on how sensitive surveillance and high coverage prevent a comeback anywhere.
Key Takeaways
- The WHO Regional Office for Africa confirmed on 19 August 2026 the closure of poliovirus type 2 outbreaks in Burundi, Ghana, Guinea-Bissau, Republic of the Congo and Uganda after OBRA assessments between January and June 2026.
- All five outbreaks were due to circulating vaccine-derived poliovirus type 2 (cVDPV2), which emerges when the weakened oral polio vaccine virus mutates during prolonged transmission in under-immunised communities.
- Outbreak closure requires at least 12 months with no detection of the outbreak strain from any source and high-quality AFP and environmental surveillance, verified by an independent Outbreak Response Assessment (OBRA) team of 5 to 8 external experts.
- Guinea-Bissau has reported no poliovirus since July 2021 and Republic of the Congo since December 2023, while Burundi declared its outbreak in March 2023 and Uganda detected virus in May 2024.
- The Global Polio Eradication Initiative (GPEI), launched in 1988, and the Africa Regional Certification Commission certified the WHO African Region free of indigenous wild poliovirus on 25 August 2020, with only WPV1 still endemic in Afghanistan and Pakistan.
