A child is vaccinated during a nationwide vaccination campaign in Jabuary 2022. Seven national and one sub national campaigns have taken place since 15 August last year. © WHO/Afghanistan
A child is vaccinated during a nationwide vaccination campaign in Jabuary 2022. Seven national and one sub national campaigns have taken place since 15 August last year. © WHO/Afghanistan

Wild poliovirus transmission in Afghanistan is currently at its lowest level in history. Fifty six children were paralysed by wild polio in 2020. In 2021, the number fell to four. This year to date, only one child has been paralysed, giving the country an extraordinary opportunity to end polio.

The resumption of nationwide polio vaccination campaigns targeting 9.9 million children has been a critical step. Since 2018, local-level bans on polio vaccination activities in some districts controlled by the Taliban had significantly reduced the programme’s ability to vaccinate every child across the country. With access to the entire country following the August transition, seven nationwide vaccination campaigns took place between November 2021 and June 2022, and a sub national campaign targeting 6.7 million children in 28 provinces took place in July. Of the 3.6 million children who had been inaccessible to the programme, 2.6 million were reached during the November, December and January campaigns. With improved reach to previously inaccessible children throughout the February to July campaigns, the number children has been reduced to 0.7 million. Further campaigns are planned for the remainder of the year.

With Afghanistan and Pakistan sharing one epidemiological block, the two countries continue to coordinate cross border activities. December and May’s campaigns were synchronized with Pakistan’s national campaigns, focusing on high risk populations including nomadic groups, seasonal workers and communities straddling both borders.

Improved access also had a significant impact on polio surveillance activities. Afghanistan’s surveillance indicators remained above global standards throughout the transition. With access to all districts since August, the quality of activities has improved significantly including early case detection and reporting.

In June, the first review of the polio surveillance system in six years took place with WHO hosting a team of technical experts including epidemiologists and virologists. A small team visited in 2016 but insecurity and lack of access to much of the country limited the visitors’ movements to Kabul, Herat, Kandahar, Jalalabad, Mazar-e-sharif and Kunduz. This year, the 16-strong team visited 76 districts across 25 of the country’s 34 provinces. The review determined the likelihood of undetected poliovirus transmission in Afghanistan to be low. Recommendations, including upscaling surveillance in the country’s south and south east, are being implemented.

With more than twenty years on the ground in Afghanistan, the polio programme continues to leverage its extensive operational capacity to deliver better health outcomes for all Afghans. In the face of an unprecedented humanitarian crisis, in addition to day-to-day polio activities, polio staff continue to regularly monitor the functionality of health facilities across the country as well as support ongoing vaccination campaigns including measles and COVID 19. WHO’s polio team in the southeast were among the first responders following the devastating earthquake in Paktika and Khost provinces in June. In addition to providing critical health care, the team’s experience working among local communities provided the foundations of an assessment tool that mapped affected communities and ensured accurate data guided a focused response in the immediate aftermath.

Although the number of children paralysed by polio has reduced significantly in Afghanistan, the threat is far from gone and the programme faces significant challenges. While access has improved across the country, accessing every child though house to house vaccination remains a challenge in some areas leaving immunity gaps and, with them, children at risk.

On 24 February, eight polio workers were killed in targeted attacks in the country’s north, not the first time polio workers had come under attack in the course of their life saving work. Four of those killed were women. Female polio workers play a critical role in the programme, building community trust and reaching all children.

The sharp rise in the number of wild polio cases in Pakistan is a cause for concern, and the detection of one case each in Malawi and Mozambique is a reminder of the continued risks of poliovirus and the urgencyrequired to permanently interrupt transmission in both Afghanistan and Pakistan.

While the polio programme has made important progress in the last 12 months, sustaining those gains with high quality campaigns that vaccinate all children and build enough immunity to end circulation of the virus for good is critical. A polio free Afghanistan is within reach – but there is still a long way to go.

The discovery in the summer of 2022 that poliovirus had been found in sewers in London as well as in an unvaccinated community in New York startled many who had long forgotten about polio. The outbreak was a perfect demonstration that vaccines are often so successful at stopping deadly diseases, that we can be lulled into a false complacency.

Although the disease is now endemic only in Afghanistan and Pakistan, it was a dangerous childhood disease across the world for much of the late 19th and early 20th centuries. Although polio vaccines were introduced as routine immunisations in the 1970s, which reduced cases substantially, by the late 1980s, polio still was paralysing over 1,000 children a day.

In 1988, the launch of Global Polio Eradication Initiative (GPEI, of which Gavi is a member) had a galvanising effect on efforts to eliminate the disease, bringing together governments, donors, local communities and health workers in a joint effort to raise awareness of the disease and widen access to polio vaccines.

Cases began to drop dramatically and are down 99%, with most countries having zero cases. An estimated 20 million children have been prevented from getting polio since the GPEI was launched. When Nigeria was declared free of wild poliovirus in 2020, it was a major achievement: it had been one of the last few countries where the disease had clung on.

As remarkable as these successes have been, polio experts warn that there is no room for easing off on eradication efforts until the world is polio-free. Infectious diseases that are nearly wiped out can bounce back with alarming ease when the global circumstances change – measles rates have started climbing in the past few years as vaccination rates have fallen in Europe and the US.

Uneven polio vaccine coverage across the world, compounded by the COVID-19 pandemic’s toll on routine immunisation worldwide, has meant the disease has popped up in unexpected places. In October 2021, Ukraine saw an outbreak, followed by a case of wild poliovirus in February 2022 in Malawi. In March, vaccine-derived polio was spotted in Israel, and in Pakistan, where the disease is still entrenched, more polio cases were recorded in the first quarter of 2022 than in the whole of 2021.

Although polio only affects a handful of countries currently, the potential threat from its continued circulation means that the World Health Organization still classifies it as a Public Health Emergency of International Concern (PHEIC) despite this classification being given back in 2014.

An ancient disease

Polio is one the world’s oldest diseases – 14th century Egyptian engravings have been found depicting a priest with a withered leg, the trademark of a disease that can paralyse the leg, leading to muscle weakness and shrinking. The British physician Michael Underwood produced the first clinical description of the disease in 1789. In 1840, the German orthopaedic doctor Dr Jacob Von Heine understood that poliomyelitis was a distinct disease from other forms of paralysis and theorised it had an infectious cause. The poliovirus that causes the disease was identified in 1909 by Austrian immunologist Karl Landsteiner.

The disease is caused by a highly infectious virus that spreads when people ingest food or water contaminated by human faeces, or through poor hygiene. Because of this it is common in areas where there is poor access to clean water and sanitation.

The virus mostly affects children. Around 70% of infections are asymptomatic or cause mild symptoms such as headache, fever, and neck stiffness, but it can also invade the nervous system and cause paralysis and, in extreme cases when the person’s breathing muscles are paralysed, it can kill. In some survivors, the nerve damage can cause post-polio syndrome, a disorder in which they may have muscle weakness that deteriorates over time, causing pain and fatigue and leaving them disabled.

There are three wild types of poliovirus (WPV) – type 1, type 2, and type 3. Type 2 was declared eradicated in September 2015, with the last case detected in India in 1999. Type 3 was declared eradicated in October 2019, having last been detected in November 2012. Type 1 remains in Afghanistan and Pakistan.

Vaccine development

There are two types of polio vaccines – an inactivated (killed) polio vaccine (IPV) developed by Dr Jonas Salk and first used in 1955, and a live attenuated (weakened) oral polio vaccine (OPV) developed by Dr Albert Sabin and first used in 1961.

IPV is made from inactivated wild-type poliovirus strains of each type; it is an injectable vaccine and in many countries is given with other routine childhood immunisations such as against diphtheria, tetanus and pertussis.

OPV consists of a mixture of live attenuated poliovirus strains of each of the three serotypes. It is safe and effective, however, the use of OPV in areas with poor water and sanitation can occasionally have an unwanted side effect – the live vaccine-virus shed by vaccinated individuals can in very rare cases mutate and spread in communities that are not fully vaccinated against polio.

The lower the population immunity, the longer the vaccine-derived virus can spread. This version of the virus can sometimes regain its ability to damage the nervous system and lead to paralysis – this is called a circulating vaccine-derived poliovirus (cVDPV).

Although IPV is an effective vaccine and valuable in countries with zero incidence of polio, it is better used as a precaution, since it does not trigger the same immune response as OPV and therefore is not as effective in stopping active poliovirus transmission. OPV induces mucosal immunity in the intestine, the primary site where poliovirus replicates – in this way, the vaccine prevents shedding of the virus into the environment and can limit or stop person-to-person transmission. This is critical in communities with poor water and sanitation, where people are more likely to be exposed to water-borne pathogens.

Thus, although IPV has has recently been introduced into routine immunisation programmes in Gavi supported countries, OPV is still needed in countries where transmission needs to be stopped.

The last mile to eradication

The polio eradication effort was badly hit by the pandemic, but is now regaining ground. One new weapon in the arsenal is a new vaccine – the novel oral polio vaccine (nOPV2) – which has been modified to be more genetically stable than the Sabin strain and less likely to cause cases from vaccine-derived virus.

In November 2020, nOPV2 received a recommendation for use under WHO’s Emergency Use Listing (EUL) procedure to be able to roll it out rapidly. As of June 2022, approximately 370 million doses of nOPV2 have been administered in 20 countries – including Benin, Cameroon, Congo, Djibouti, Egypt, Ethiopia, The Gambia, Guinea-Bissau, Liberia, Mauritania, Mozambique, Niger, Nigeria, Senegal, Sierra Leone, Tajikistan and Uganda.

The high demand for this vaccination, however, is causing a supply constraint that the GPEI is working to ease. The GPEI advises that in situations where there is co-circulation of poliovirus strains, trivalent oral polio vaccine (tOPV) may be the best choice of vaccine.

Considerable challenges remain in eradicating polio in the two endemic countries. In Pakistan, difficulties in accessing high-risk mobile communities remain, and this is exacerbated by people refusing to get their children vaccinated because of misinformation or community fatigue, as well as low routine immunisation coverage in some parts of the country.

Afghanistan shares many of these challenges, including vaccine hesitancy, with the added challenge of decades of conflict and insecurity leading to fragile health systems that are unable to sustain routine immunisations. This has meant that many communities are missed or under-vaccinated, leaving children at risk of polio.

Now that polio vaccination programmes have resumed, eradication efforts have stepped up, ramping up vaccine coverage by boosting vaccine supply and engaging the trust of communities to overcome misinformation and raise awareness of the need for the vaccine, which can mean bringing in community and religious leaders.

The last mile to ending polio has been in sight for years, but the pandemic has thrown progress off course. While the road to eradication remains challenging, the ability of polio to re-emerge unexpectedly proves the need to continue to strive towards ensuring a polio-free world. For now, the disease is endemic in two low-income countries; there is no guarantee it will stay that way.

Reposted with permission from: www.gavi.org/vaccineswork

Children under 5 years vaccinated with nOPV2 in the Lakeside city of Aguegue (Oueme Department) © WHO/Benin
Children under 5 years vaccinated with nOPV2 in the Lakeside city of Aguegue (Oueme Department) © WHO/Benin

When it comes to stopping polio outbreaks, speed is everything. Rapid action within a specific window of time is critical. Malawi declared a public health emergency in February after uncovering a case of wild poliovirus type 1 (WPV1) – its first in 30 years. The country sprang into action, leading the charge in a multi-country vaccination response aiming to reach more than 23 million children in the sub-region with bivalent oral polio vaccine (bOPV). Three months later, neighbouring Mozambique which has been part of the same response, declared its own emergency after the virus paralyzed a child on its home soil. The country is doubling down on efforts to protect its children.

The nimble actions of the south-eastern African nations have been lauded by the GPEI as examples of what must be done to effectively quash circulation of the highly infectious poliovirus.

“Indeed Malawi has moved quickly; thus far we haven’t seen further detection of WPV1 in the country,” said Dr Modjirom Ndoutabe, Polio Programme Coordinator a.i., WHO AFRO. “It is important that further campaign rounds are carried out as planned and reach all targeted children to boost immunity in Malawi and its surrounding countries, and we’re working with governments to maintain heightened surveillance sensitivity so that we can closely track this virus through this outbreak period,” he added.

“What we’ve seen in Malawi and Mozambique following their detections, but also Tanzania, Zambia and Zimbabwe engaged in the response is encouraging. The need for speed in recognizing and communicating the public health threat and conducting quality vaccination campaigns to protect children cannot be understated,” said Aidan O’Leary, Director of WHO’s polio eradication programme.

Addressing a dual threat

Wild poliovirus is not the only form of poliovirus facing the African Region, or the world at large. Outbreaks of circulating vaccine-derived poliovirus (cVDPV) continue to pose an equally menacing threat to countries. Through rollout of a new vaccine to counter the most prevalent form of these outbreaks, cVDPV2, transmission has been stopped in the majority of countries that have deployed the tool. Additionally, a significant number of outbreaks have been recently closed following use of the traditional monovalent oral polio vaccine type 2 (mOPV2).

“WHO African Region’s Rapid Response Team (for polio) recently conducted a review of polio outbreaks over the past two years, looking at time passed since last virus detections in infected countries, surveillance quality indicators, and immunization response quality and immunity profiles of populations. I am pleased to say that 32 separate emergences of cVDPV in the Region have been declared closed across 13 countries in Africa,” said Dr Ndoutabe.

“Closure of these cVDPV outbreaks is testament to the work that has gone into achieving the high levels of vaccination coverage needed to stop transmission, and efforts to sharpen surveillance for the disease. It also illustrates the effectiveness of the vaccines we have to do the job,” said O’Leary. “Regardless of which tool is used, GPEI urges all countries affected by poliovirus to act without delay, in line with timelines contained in its SOPs for outbreak response. We must ensure that actions are commensurate with the public health emergency that polio is, despite challenges,” he reiterated.

Both viruses found in Malawi and Mozambique stem from WPV1 that was circulating in endemic Pakistan in 2019 and 2020. Though wild poliovirus cases are dwindling – currently at the lowest level in history – the fresh detections underscore both the danger of importation and the need to finish the job.

As a result of ongoing disease surveillance, the Global Polio Laboratory Network (GPLN) has confirmed that a child in Changara district, Tête province, Mozambique, was paralyzed by type 1 wild poliovirus (WPV1). 

The child experienced onset of paralysis on 25 March 2022, and sequencing of the virus confirms that it is linked to the imported WPV1 case confirmed in Malawi in February.  

While this detection of another WPV1 in the southeast Africa region is a concern, it is not unexpected following the Malawi detection in February and further underscores the importance for all countries to prioritize immunization of children against polio. 

Mozambique has participated in the multi-country coordinated vaccination campaigns in response to Malawi’s imported WPV1, with two vaccination rounds already conducted. The most recent took place at end of April, with 4.2 million children vaccinated across the country, and the Global Polio Eradication Initiative (GPEI) is supporting countries to strengthen disease surveillance and prepare for the remaining two campaign rounds. These will cover Malawi, Tanzania, Mozambique and Zambia, with Zimbabwe joining the later rounds to ultimately help reach over 23 million children under five years with polio vaccine by end of August 2022. 

Mozambique last recorded a case of wild polio in 1992 though the country has more recently been affected by an outbreak of circulating vaccine-derived poliovirus type 2 (cVDPV2). Three cases have been detected since April 2021 and vaccination campaigns in response to the outbreak are continuing, which include use of the novel oral polio vaccine type 2 (nOPV2).  

Wild polio remains endemic in just two countries – Pakistan and Afghanistan. The WPV1 detection in Mozambique does not affect the WHO African Region’s wild poliovirus-free certification status officially marked in August 2020, as the virus strain originated in Pakistan. However, any child paralysed by polio is one too many. The polio eradication programme has seen importations from endemic countries to regions that have been certified wild poliovirus-free in the past and has moved quickly to successfully stop transmission of the virus in these areas. 

Polio anywhere is a threat to children everywhere. It is vital that all parties ensure that the GPEI has the support it needs to implement its five-year eradication Strategy in full and ensure no child is paralysed by polio ever again.

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.