News Category: Circulating vaccine-derived poliovirus

Children in Vakhsh region in Tajikistan receiving their first dose of oral polio vaccine. © WHO / Mukhsindzhon Abidzhanov
Children in Vakhsh region in Tajikistan receiving their first dose of oral polio vaccine. © WHO / Mukhsindzhon Abidzhanov

Infectious diseases like poliomyelitis (polio) know no borders. Importation and subsequent spread of the virus led to the paralysis of 34 children, and 26 others tested positive without developing symptoms of paralysis. Extensive immunization efforts began in February 2021, and no child, adult or environmental sample in Tajikistan has tested positive since August 2021.

The outbreak in Tajikistan marked the first detection of circulating vaccine-derived poliovirus type 2 (cVDPV2) in the WHO European Region. It is now the first cVDPV2 outbreak in the world to be declared officially closed following supplemental immunization using the novel oral polio vaccine type 2 (nOPV2).

The Region has been free of endemic poliovirus since 2002. Detection of just 1 case of polio – whether from a wild or vaccine-derived poliovirus – is considered an outbreak, and requires an immediate and comprehensive response.

“Tajikistan’s success in stopping this outbreak is a major achievement and a clear demonstration of the highest level of political commitment of the Government of Tajikistan,” says Dr Hans Henri P. Kluge, WHO Regional Director for Europe.

“This outbreak and the subsequent response came at a time when the health system was already overstretched by the COVID-19 pandemic and the country was mounting a massive COVID-19 vaccination drive. Both outbreak responses had to be done without disrupting the vitally important provision of other routine vaccines to children. We acknowledge the efforts of the Ministry of Health over the past several years, which resulted in a resilient immunization system able to successfully manage all these competing immunization priorities.”

Actions taken to stop the outbreak

Following confirmation of the outbreak, the Ministry of Health and Social Protection of the Population took immediate steps, with support and guidance from WHO and other Global Polio Eradication Initiative partners. Actions included enhanced poliovirus surveillance, intensive contact tracing and a thorough review of immunization coverage at subnational levels. A rigorous risk assessment was conducted to determine the outbreak response scale and choice of vaccine, and the country rapidly completed a comprehensive verification process for readiness to use the nOPV2 vaccine.

In February 2021, a high-quality nationwide inactivated polio vaccine campaign was conducted to close the immunity gap against poliovirus type 2 among the more than half a million children born from 2016 to 2018 who had been left vulnerable as a result of global inactivated polio vaccine (IPV) supply constraints following cessation of trivalent oral polio vaccine use.
From June to September 2021, 2 nationwide and 1 subnational nOPV2 immunization rounds were implemented for all children under 6 years of age, with coverage confirmed (through external assessment) to be greater than 95%. Extensive social mobilization and communication strategies were deployed to reach groups who were at risk of being missed, including internal migrants in urban areas and unregistered children.

Assessment of the outbreak response

Several criteria must be met to officially close an outbreak, including at least 6 consecutive months in which no poliovirus is detected. The independent experts of the Global Polio Eradication Initiative who conducted the assessment in Tajikistan also looked at the performance of routine polio vaccination, the coverage achieved during the supplemental immunization rounds, and the capacity and sensitivity of the polio surveillance system to detect any poliovirus circulation.

Following the thorough assessment, which included briefings at the national level and field visits to national referral hospitals, public hospitals, polyclinics, regional and district immunization programme offices, and public health centres, the team recommended closure of the outbreak.

nOPV2 – a new chapter in global efforts to eradicate polio

Ending this outbreak using nOPV2 is an important milestone for the global polio programme. The innovative vaccine is a key part of the new strategy to stop cVDPV2s. Clinical trials show that nOPV2 is safe and effective, and more genetically stable than the traditional type 2 oral polio vaccine.

Since the rollout of nOPV2 began in March 2021, over 265 million doses have been administered across 14 countries. The majority of countries using the vaccine have also managed to stop transmission of cVDPV2; however, this is the first official closure of an outbreak to take place following nOPV2 use.

In addition to successfully halting transmission and lowering the risk of infection for millions of people, Tajikistan contributed to global research on nOPV2 with the support of WHO through an nOPV2 immunogenicity study. The country also participated in a global vaccine wastage study.

April 2022 – Convening this month in Geneva, Switzerland, the Strategic Advisory Group of Experts on immunization (SAGE), the global advisory body to the World Health Organization (WHO) on all things immunization, urged concerted action to finish wild polioviruses once and for all.

The group, reviewing the global wild poliovirus epidemiology, highlighted the unique opportunity, given current record low levels of this strain. At the same time, it noted the continuing risks, highlighted in particular by detection of wild poliovirus in Malawi in February, linked to wild poliovirus originating in Pakistan.

On circulating vaccine-derived poliovirus (cVDPV) outbreaks, SAGE expressed concern at continuing transmission, in particular in Nigeria which now accounts for close to 90% of all global cVDPV type 2 cases, as well as the situation in Ukraine, and its disruption to health services, urging for strengthening of immunization and surveillance across Europe.  It also noted the recent detection of cVDPV type 3 in Israel in children, and in environmental samples in occupied Palestinian territories, and urged high-quality vaccination activities and strengthened surveillance.

Preparing for the post-certification era, the group underscored the importance of global cessation of all live, attenuated oral polio vaccine (OPV) use from routine immunization, planned one year after global certification of wild poliovirus eradication.  To ensure appropriate planning, coordination and implementation, the group endorsed the establishment of an ‘OPV Cessation Team’, to consist of wider-than-GPEI stakeholder participation and ensure leadership on all aspects of OPV cessation.

SAGE will continue to review available evidence and best practices on a broad range of GPEI-related programmatic interventions, including as relevant the increasing role of inactivated polio vaccine (IPV), including in outbreak response and effects of novel oral polio vaccine type 2 (nOPV2), as part of global efforts to secure a lasting world free of all forms of poliovirus.

On 21 March, the Federal Government of Somalia, World Health Organization (WHO) and members of the Global Polio Eradication Initiative (GPEI) recommitted to stopping the ongoing outbreak of circulating poliovirus type 2 (cVDPV2) in Somalia at a three-day meeting convened in Nairobi, Kenya. High-level delegates at the meeting included HE Fawziya Abikar Nur, Federal Minister of Health and Human Services, Dr Mamunur Rahman Malik, WHO Representative to Somalia and Head of Mission, alongside senior representation from the Bill & Melinda Gates Foundation (BMGF), the Centers for Disease Control and Prevention (CDC), Rotary International, Save the Children, the United Nations Children’s Fund (UNICEF), and other UN agencies and partners.

Together, the Government, GPEI partners, which include WHO, UNICEF, the BMGF, CDC, Rotary International, GAVI, the Vaccine Alliance, and other key partners endorsed the Somalia Polio Eradication Action Plan 2022 to reaffirm their commitment.

The Somalia Polio Eradication Action Plan 2022 outlines a four-point call to action to stop the spread of the current outbreak, which is one of the longest lasting cVDPV2 outbreaks to be reported so far. The robust plan aims to direct partners’ efforts and resources towards boosting population immunity, making concerted efforts to reach high-risk populations — including inaccessible and nomadic communities and internally displaced persons — to strengthen their immunity, enhancing the search for poliovirus circulation, and strengthening coordination among all stakeholders. Some of the strategies that will be deployed include intensifying efforts to offer 5 opportunities for vaccination against polio in 2022, providing routine childhood immunization in high-risk locations, where children have missed out on vaccinations, and strengthening community engagement. Given how easy it is for the cVDPV2 virus to spill over international borders, the emergency plan also advocates for stronger cross-border coordination among the polio eradication programmes in Somalia, Kenya, Ethiopia and Djibouti.

“In the midst of the ongoing drought, and while recovering from the effects of the COVID-19 pandemic, our stakeholders must not forget how important it is to contain the ongoing poliovirus outbreak so that it does not spread any further and does not affect any more children’s lives,” said HE Fawziya Abikar Nur, Federal Minister of Health and Human Services. “On this occasion, I would like to extend my sincere gratitude to all our partners, and donors, for the immense efforts they have put into shielding millions of Somali children from polio over the years.”

“Since its inception 25 years ago, Somalia’s polio eradication programme has made progress, including by stopping outbreaks of wild poliovirus and, recently, one of circulating poliovirus type 3 in 2021. The programme has established a vast network of polio workforce and assets and we can do more not only to stop the current outbreak but to achieve broader health system goals through integration and effective use of our human and operational resources. Since 2018, Somalia has conducted several supplementary immunization campaigns. Despite these efforts, pockets of unvaccinated children remain, due to insecurity and limited access to health services,” said Dr Mamunur Rahman Malik, WHO Representative to Somalia.

The Somalia Polio Eradication Action Plan, which will be implemented in 2022, complements one of the goals outlined in the GPEI ‘Polio Eradication Strategy 2022–2026: Delivering on a Promise’, to stop cVDPV transmission and prevent outbreaks in non-endemic countries. It is also in line with Somalia’s national goals and UN Sustainable Development Goals (SDGs).

17 March 2022 — On Monday 7 March 2022, a case of circulating vaccine-derived poliovirus type 3 (cVDPV3) was confirmed in an unvaccinated girl aged three years and nine months in Israel. The girl had developed acute flaccid paralysis and upon testing of her stool, poliovirus was confirmed.

Further testing of the virus isolated from the girl revealed genetic links to VDPV3-strains detected in environmental samples collected between September 2021 and January 2022 from sites in Jerusalem and Bethlehem.

Circulating VDPV3 has also been confirmed in a sample taken from a contact in Jerusalem.  This child does not display any symptoms of paralysis.

A previous statement published on 10 March 2022 had indicated circulation of this VDPV3 also in occupied Palestinian territory; further field investigations concluded that at this time, circulation can only be confirmed in Israel.  This classification does not however change the risk this cVDPV3 presents to children in Israel and in the occupied Palestinian territory, nor the planned response activities.

 Although there is currently no evidence of circulation of this cVDPV3 in occupied Palestinian territory, the proximity and interconnectedness of communities on both sides of the border and the volume and frequency of cross-border population movement underscore the risk to unvaccinated children in both places.

Local health authorities in both Israel and occupied Palestinian territory are conducting field, epidemiological and virological investigations, to determine more clearly the source and origin of the isolated virus and potential risk of further spread associated with it. Discussions are ongoing to plan an immunization response as appropriate (extent and scale to be determined, potentially to include a series of immunization outreaches with both inactivated polio vaccine and bivalent oral polio vaccine, both in high-risk areas of Israel and occupied Palestinian territory).  At the same time, efforts are continuing to strengthen surveillance comprehensively in both Israel and occupied Palestinian territory.

Experts from headquarters, regional and country offices of the Global Polio Eradication Initiative (GPEI) partnership, which includes WHO, Rotary International (RI), the US Centers for Disease Control and Prevention (CDC), the United Nations Children’s Fund (UNICEF), Bill & Melinda Gates Foundation (BMGF) and Gavi, the Vaccine Alliance, are working together to help ensure an appropriate response and cessation of this outbreak.

Detection of this cVDPV3 underscores the importance of strong disease surveillance and high population immunity levels, in order to minimize the risk and consequences of any poliovirus introduction or emergence.

The GPEI partnership urges all health authorities to enhance surveillance for poliovirus and implement enhanced vaccination response to prevent further transmission, so that no child is at risk of lifelong paralysis from a disease that can so easily be prevented. GPEI is committed to assisting the health authorities in their efforts to stop the cVDPV3 outbreak.