What would it take to eradicate polio finally?
What would it take to eradicate polio finally?
Are you wondering what it would take to eradicate polio finally? They were both brilliant scientists who were so committed to their mission of eliminating polio that they had injected themselves and their loved ones with weakened strains of the virus. Despite this, Albert Sabin and Jonas Salk had a heated competition; Sabin even joked that Salk's achievements could be made in a kitchen sink.
They were at odds because of divergent opinions on how best to protect the public against polio through vaccination. Salk theorized that a vaccine in which the virus particles had been chemically inactivated, rendering them incapable of replicating or causing disease, was the way to go. Sabin advocated using a "live" oral vaccine, which contains live but weakened virus particles that can reproduce but cannot induce paralysis.
After initial success in animal studies, Salk's inactivated polio vaccine (IPV) was tested on humans and given the green light. Sabin's oral polio vaccine (OPV) was the backbone of international efforts to eradicate the disease and is often credited with bringing it to the verge of extinction. COVID-19, persistent violence, and political uncertainty have allowed polio the breathing room needed to mount a comeback. This time, researchers are banking on combining Salk's and Sabin's strategies to eradicate polio.
Fighting polio
A rapid decline in polio cases was observed before the COVID-19 epidemic. Moreover, half a million people worldwide, usually children, were killed or left permanently disabled by polio every year during the 1940s and 1950s when the disease was at its peak. The widespread provision of inactivated poliovirus (IPV) vaccination and, later, live attenuated oral poliovirus (LAOPV) vaccine led to a precipitous decline in the incidence of polio in high-income countries during the 1960s and 1970s (OPV).
However, the fight against polio did not begin until the 1980s. According to studies conducted in communities and schools, one in every 200 polio infections back then caused paralysis, making it the top cause of paralysis in low-income countries. Global polio eradication efforts began in earnest in 1988 when the World Health Assembly passed a resolution calling for the disease to be eradicated worldwide. A public-private partnership known as GPEI was established to that end. GPEI, headed by national governments and backed by the WHO, Rotary International, the US CDC, UNICEF, and, more recently, the bill & Melinda gates foundation and Gavi, The Vaccine Alliance, has achieved significant gains in protecting communities from polio through broad OPV campaigns.
Over this period, polio cases have decreased by 99.9 per cent, and GPEI and its partners have accomplished what many thoughts was impossible: they have eradicated polio from all but a handful of nations.
The final stage of eradication
Wild poliovirus type 3 (WPV3), one of three types of the virus, was declared eradicated worldwide in 2019 by an independent commission of specialists. After the last case of Type 2 poliovirus was discovered in India in 1999, the virus was declared eliminated in September 2015, leaving only the Type 1 wild poliovirus to roam free in Pakistan and Afghanistan.
After a lengthy vaccination and surveillance programme, the World Health Organization (WHO) declared in August 2020 that all 47 nations in its Africa Regions were certified wild poliovirus-free. This was during the height of the fight against COVID-19. In Afghanistan and Pakistan, wild poliovirus was now solely endemic (present in the environment through natural means).
However, more than 1,100 children became paralyzed due to increased outbreaks of circulating vaccine-derived poliovirus (cVDPV) between 2019 and 2020. This unique form of polio exclusively arises in places with low vaccination coverage. Limited community transmission of cVDPVs has been observed this year in the United Kingdom, the United States, and Israel. Cases of wild poliovirus have been found in Malawi and Mozambique, both in southeast Africa.
Dr Tedros Adhanom Ghebreyesus, the Director-General of the World Health Organization, indicated that the resurgence of polio could happen worldwide because of the recent cases found in nations that had previously been clear of the disease. Stay the course and eradicate polio for good, remembering the enormous obstacles we've already surmounted along the way.
As disappointing as these setbacks are, they have finally served as a wake-up call to GPEI and its allies, reinvigorating their efforts to eradicate polio. "I think the past two years have proved very clearly that there is a finite window to prevent polio transmission and accomplish the job," said Aidan O'Leary, WHO's Director for Polio Eradication. This virus will spread again if we fail to wipe it off.
First, the Global Polio Eradication Initiative (GPEI) aims to terminate poliovirus transmission in Pakistan and Afghanistan by 2023 permanently. Second, The GPEI seeks to eliminate cVDPV transmission and prevent epidemics by 2023. By 2026, we want to say that the globe will be polio-free, which means that no new cases have been found.
These objectives can only be met by a vast and coordinated effort in which both OPV and IPV play crucial roles.
Immunization against polio
The highly contagious poliovirus begins its life cycle in the respiratory system, replicating rapidly before migrating to the gastrointestinal tract. In roughly 1 in 200 persons, it can cause irreversible nerve damage or paralysis via the circulatory system. Furthermore, some polio survivors acquire post-polio syndrome, characterized by growing muscle weakness and exhaustion, which can significantly reduce their quality of life. However, over 70% of infected people show no symptoms or exhibit only moderate ones, such as a slight fever, a headache, or a stiff neck.
Both oral polio vaccine (OPV) and inactivated polio vaccine (IPV) have significantly reduced the prevalence of polio and the illnesses it causes, but they function slightly differently. To create IPV, viral particles from all three poliovirus types were inactivated. Injecting the vaccine into an arm or leg is a highly efficient way to prevent polio from reaching the nerves and causing paralysis. However, the vaccine is not as efficient at stimulating antibodies in the intestines, so vaccinated individuals can still contract and spread poliovirus.
In contrast, the oral polio vaccine (OPV) contains a cocktail of attenuated poliovirus strains that can still reproduce but are no longer capable of causing paralysis. Oral administration of OPV stimulates the body to create antibodies not only in the digestive system but also in the circulatory system. Therefore, the poliovirus will not be able to replicate and infect other people if a vaccinated person is exposed to it in the future.
Due to its efficacy in preventing the spread of the disease, as well as its lower cost and simpler administration compared to IPV, OPV has been widely adopted in most nations and has been an instrumental factor in the successful elimination of wild poliovirus in all but a handful of locations. However, some of the weakened viruses in OPV may be expelled by vaccinated persons and transmitted to unprotected ones, particularly in areas with poor sanitation. Due to the protective effects of immunity against weaker polioviruses, this may be a good thing.
But there are downsides as well. Any further virus transmission from vaccines quickly dies out in heavily vaccinated areas. However, weakened poliovirus could linger in the wild for months or even years in regions with lower vaccination rates. These viruses can amass genetic alterations that restore their paralyzing abilities in sporadic cases. If they continue to spread, these strains can potentially cause what is known as a circulating vaccine-derived polio outbreak.
Under-immunized
Furthermore, in the discussion of What it would take to eradicate polio finally? Rarely seen outside of under-vaccinated areas, polio caused by vaccines is an exception to the rule. Of the roughly three billion children worldwide exposed to OPV between 2000 and 2021, only 2,299 were paralyzed by cVDPV.
New OPV strains created during the past decade have been shown to mitigate the emergence of cVDPVs in the future. Since April 2016, all countries have adopted bivalent OPV, which comprises only kinds 1 and 3, instead of older forms of OPV that had weakened structures of types 1, 2, and 3. Because the weaker type 2 strain is responsible for roughly 90% of all cVDPVs, this is helpful.
Vaccine-derived polio has arisen as a significant obstacle in the final phase of polio eradication. More than 90% of all cVDPV cases worldwide are caused by the type 2 strain, concentrated in three specific regions: northern Yemen, the places like eastern DRC and northern Nigeria. Another issue is the ongoing fighting in central and southern Somalia.
"In all the regions where we confront challenges, it is due to a mix of concerns around inaccessibility and security, non-functioning health services, and communities who have gotten marginalized from the state, for a whole variety of reasons," O'Leary said.
The Houthi leadership in Sanaa, Yemen's capital and largest city, has imposed severe limitations on the practice of vaccinating children, making the situation there highly alarming. A delay of almost a year has allowed the virus to propagate in cases where the vaccination system is either nonexistent or poorly functioning. We understand that the removal of these restrictions may be forthcoming. "It's wreaked devastation, resulting in over 200 paralyzed youngsters," O'Leary added.
Not only are these cVDPV hotspots dangerous in and of themselves, but international travel also makes it possible for infections to spread to other areas, which may explain the latest detections of cVDPV in London, New York, and Israel. The good news is that the same strategies successfully eradicated wild poliovirus can also be used to halt future outbreaks, including increasing polio surveillance and guaranteeing high vaccine coverage.
Time is of the essence.
Since time is essential during an outbreak, OPV is the recommended vaccine. O'Leary emphasized OPV's simplicity, low cost, effectiveness, and safety. "Especially the children we worry about the most, those under the age of two, it is not an easy chore to transport them — sometimes very extensive — to obtain an injectable vaccine in a clinic. Therefore, we invert the process and deliver vaccines to individuals' homes to facilitate easy and efficient immunization and maximize the available coverage.
The recent development of another new OPV, designated type 2 novel oral polio vaccine (nOPV2), intended to extinguish cVDPV2 outbreaks more sustainably, should substantially lower the chance of new cVDPVs arising during these emergency campaigns. This OPV, like its predecessors, contains attenuated type 2 polioviruses. Still, the viruses have been further changed to make them more stable, making it far less probable that they would relapse into a dangerous form.
The Polio Eradication And Endgame Strategic Plan called for the progressive withdrawal of the current Sabin-strain oral polio vaccine (OPV) to reduce the primary risk of the emergence of all types of vaccine-derived polio cases. The vaccine itself poses no threat; low vaccination rates pose a danger. If a whole population receives vaccinations, they will be safe against both the polioviruses found in the vaccine and those found in the wild.
Methods for the deciding round
In the long run, however, OPV will be completely phased out. The issue is not the vaccine but relatively low immunization rates and the potential emergence of new cVDPVs.
Here comes intimate partner violence (IPV). To ensure that polio does not return, even though it has been eradicated in most countries and continents, routine childhood immunization with IPV is essential. This is true for children who have already been vaccinated against polio and those who will be born in the future.
According to O'Leary, IPV provides the cavalry needed to finish the job: "It needs to be greatly boosted up everywhere, to sustain the advances that have been made." OPV has been the artillery in the war against polio. Therefore, it is crucial to improve vaccination programmes worldwide.
These efforts were moving quickly before the COVID-19 outbreak derailed them. With Gavi's help, Nepal was the first country to implement routine IPV immunization in 2014. Every country that received funding from Gavi was able to introduce the vaccine and immunize its children within five years, saving more than 112 million lives.
However, the distribution of all standard childhood immunizations has been delayed because of the COVID-19 epidemic. O'Leary noted that there had been a dramatic increase in the number of children classified as zero-dose, indicating they have not received any of the usual immunizations, from less than 19 million to more than 25 million.
We're in the home stretch now
In its new road map, The Polio Eradication Strategy 2022-2026, GPEI has pledged to reverse this trend by swiftly rebuilding coverage rates in those locations where gaps are being documented.
It remains to be seen if GPEI and its partners can make up enough ground to terminate global transmission of wild poliovirus by the end of 2023. Still, their determination and commitment to run the final mile are unyielding.
It's not the first time such goals have been proposed. Gavi's CEO, Seth Berkley, has stated that the initiative's new strategy will emphasize finding targeted ways to reach overlooked communities and seizing possibilities to become more integrated with other essential services. In these areas, "children regularly lack access to a wide variety of crucial health interventions and vaccines," not simply polio vaccinations.
If polio is successfully eradicated, it will join smallpox as the only other human illness to be eliminated from the planet. While the COVID-19 epidemic and other obstacles may make it seem impossible, O'Leary is optimistic that success is still possible. And "both kinds of immunization are definitely necessary."
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