Africa has eradicated wild polio

Image credit: Kruthika Sundaram

There were massive challenges faced during the campaign to eradicate wild polio. To be truly effective, vaccination efforts had to reach far out and potentially dangerous regions, which led to deaths among front-line workers and volunteers. Patients who were hardest to reach were usually those most vulnerable, mostly displaced by conflict. Misinformation was combatted in part by polio survivors, such as the Nigerian Polio Survivors Association, which helped educate and warn communities of the dangers and consequences of polio.

On August 25th, the African Regional Certification Commission (ARCC) for Polio Eradication, a board appointed by the World Health Organization (WHO) African Regional Director, declared that Africa was free of wild (type 1) polio. This milestone was reached through extensive vaccination campaigns, education on the importance of immunization, increased laboratory and storage capacity, polio survivor’s initiatives, and many other components. 

The WHO first launched the Global Polio Eradication Initiative (GPEI) in 1988. The Organization of African Unity endorsed the WHO’s GPEI in 1996 and Nelson Mandela, the President of South Africa at the time, supported the initiative with the “Kick Polio Out of Africa” campaign. Backed by Rotary International and many other organizations, there was a large mobilisation of front-line workers and volunteers to immunize communities and educate them on the poliovirus.  

The ARCC set forth guidelines to verify and maintain the eradication of poliovirus in affected countries. For example, the maintenance of high immunisation rates and at least 3 years free of wild polio transmission. The last cases of polio were reported between July and August of 2016, in the Borno State of Nigeria, the last country in the African Region to be declared polio free. After two field expeditions to Nigeria and revision of documentation provided by the Nigerian government, the ARCC for Polio Eradication confirmed that Nigeria was free of wild polio. 

What is polio?

Poliovirus causes poliomyelitis, also known as polio, a disease that mainly affects children under the age of 5. This disease can lead to irreversible paralysis due to nervous system damage and even death in 5 to 10 percent of cases, where the paralysis of muscles involved in breathing occurs. 

In 1996, about 7500 children in Africa were left paralysed by polio, today there are no cases of wild polio in Africa. There are three types of polio: type 1, type 2, and type 3. Type 2 polio was last recorded in India in 1999 and thus declared eradicated in 2015. Type 3 was eradicated in October 2019 after the last case was recorded in November 2012 in Nigeria. Thus, with the eradication of type 1 poliovirus in Africa, type 1 poliovirus remains in only two countries: Afghanistan and Pakistan. There is no cure for polio, however, vaccination provides lifelong protection from the virus.

A child recieving an oral polio vaccine. Image credit: USAID via Wikimedia.

There are two different types of vaccination: inactivated poliovirus vaccine (IPV) and oral polio vaccine (OPV). IPV was discovered by Jonas Salk in 1955 and contains inactivated forms of all three types of polio. It needs to be injected by a trained health professional, providing low immunity in the intestines because it insights an immune response in the blood. IPV is beneficial because there is no risk of vaccine-associated paralytic poliomyelitis (VAPP), though occurrences of VAPP generally are extremely rare. Poliovirus is transmitted through the faecal-oral route, but since IPV does not provide strong immunity in the intestines, as it insights an immune response in the blood, the virus is still able to multiply and be excreted through the faeces, thus continuing its spread, especially in areas of poor sanitation.

On the other hand OPV is taken orally and provides a strong immunity in the intestine. Thus, OPV is always implemented in the event of an outbreak because it can prevent transmission and provides passive immunity. OPV was discovered by Albert Sabin in 1961 and contains all three weakened types of polio. OPV consists of a weakened form of the virus that is unable to attack the nervous system and is preferable to IPV because it does not require sterile needles, environment, or a trained health professional. Hence, OPV is the vaccine used by the GPEI.

There are some disadvantages to OPV, such as VAPP and the potential for the weakened virus form to become pathogenic again over time in communities with incomplete immunisation. The occurrence of VAPP is extremely rare (happening a couple of times in a million births) and is thought to be due to immunodeficiencies. Additionally, about 40 percent of VAPP cases were due to the type 2 component of the OPV. After the eradication of type 2 polio, the OPV was altered to contain only weakened forms of type 1 and type 3 poliovirus. However, stockpiles of the type 2 OPV are kept in secure storage.

What is vaccine-derived poliovirus?

Although Africa has been declared wild polio free, there are still cases of circulating vaccine-derived poliovirus (cVDPV). This is when the weakened poliovirus from the vaccine is allowed to circulate in the community for an extended amount of time, usually 12 to 18 months. During that time, the virus can accumulate mutations and revert to a form that can invade the nervous system. This is usually due to incomplete immunisation in a community. Just as with 40 percent of the VAPP cases being due to the type 2 component of the vaccine, around 90 percent of the cVDPV cases were also due to the type 2 weakened poliovirus. Thus, another benefit of removing the type 2 poliovirus from the vaccine is a potential reduction in cVDPV2. Most importantly, the risk of cVDPV is greatly outweighed by the benefit of being protected from polio. According to the WHO, there have been around 760 cases of VDPV in 21 countries since 2000, meanwhile in the same timespan more than 13 million cases of polio were prevented by means of vaccination. 

The GPEI has set up a new campaign titled ‘Strategy for the Response to Type 2 Circulating Vaccine-Derived Poliovirus 2020-2021’. The campaign outlines that a rapid response (within 72 hours) and extensive immunization is needed to counteract outbreaks. Thankfully, the same methods that were developed against wild poliovirus can be applied to a cVDPV2 outbreak.

Thus, the world is one step closer to having eradicated wild polio, with only two countries left. Additionally, with the new campaign in place by the GPEI, Africa may soon be declared free, not only of wild polio, but also cVDPV. This accomplishment was no small feat and was made possible by people working on a global, national, and local level. The campaign to eradicate wild poliovirus has provided a base model to use for other infectious diseases.

Written by Arianna Schneier and edited by Tara Wagner-Gamble.

Arianna’s thoughts… The eradication of wild poliovirus was no small feat and has taken over 30 years since the WHO first launched GPEI in 1988. But, the benefits surpass saving millions of lives. There is now a system in place to respond to infectious diseases with laboratories and immunisation campaign strategies. The key is to maintain these systems in the future and continue with the GPEI’s new campaign to keep cVDVP in check and eventually eradicate this form of polio too. Hopefully in our lifetime we’ll be able to add poliovirus to smallpox on the list of globally eradicated viruses. 

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