Poliomyelitis, commonly referred to as polio, is a communicable viral infection, usually infecting children, especially those under five years of age. It is transmitted essentially by direct contact with infected feces through poor hygiene or contaminated food and water. Immediately after entering the body, the virus multiplies in the intestines and can even invade the nervous system, causing paralysis.¹

Since the launch of the worldwide initiative to combat polio in 1988, the incidence of wild poliovirus has decreased by over 99%.¹ The number of cases dropped from approximately 350,000 in more than 125 countries to only six cases in 2021. Of the three types of wild poliovirus-types 1, 2, and 3-type 2 was declared eradicated in 1999 and type 3 in 2020. As of 2022, there is only one remaining type of wild poliovirus, and it remains in only two countries: Pakistan and Afghanistan.

Historical context: poliovirus as a global threat

Polio caused widespread paralysis and death, mainly in children. During the early 20th century, epidemics from polio hit with terrifying regularity, crippling thousands each year. Development of the inactivated polio vaccine by Jonas Salk in the 1950s resulted in a turn of events, drastically reducing cases in the United States. Shortly thereafter, Albert Sabin's OPV proved infinitely superior for worldwide application because it not only immunised the individual but also completely prevented the virus from being spread.²

The establishment of Global Polio Eradication Initiative (GPEI) in 1988 led to a 99% decrease in the number of polio cases compared to before. There was the hope of success in the mass vaccination campaigns like National Immunization Days which occurred in India, China, and throughout Africa. In the year 2000 for example, the Americas and Western Pacific were declared free from polio, though it is now Africa's turn to be declared in the year 2020.²

But wild poliovirus remains in Pakistan and Afghanistan, where health system challenges and political unrest have slowed eradication efforts. Despite these daunting hurdles, global cooperation has whittled the cases down from 350,000 annually in 1988 to just a few today-and brought the world closer than ever to ridding itself of the virus.²

Global Vaccination Campaigns

Starting in 1988, the Global Polio Eradication Initiative strived to eliminate polio worldwide. National Immunization Days have been one of the cornerstones of these efforts, when huge vaccination campaigns would fall and immunise children in countries endemic for polio. Huge immunisation efforts were held in countries such as China and India, sometimes vaccinating as many as tens of millions of children within days. For example, India, in its NID campaigns, had been able to reach an estimated 150 million children in a few days.³

These efforts at immunisation succeeded to a large extent through the collaborations among multi-sectors: governments, private organisations, and international partners like WHO, UNICEF, Rotary International, and the U.S. CDC that provided technical support, resources, and funds to make sure the vaccines reached the farthest areas. Coordinating cross-border immunisations was also key. This they did, and the countries within the regions with potential outbreaks, like West Africa, harmonised schedules for NIDs to avoid cross-border transmission of the poliovirus.³

By the year 2000, standardised reporting systems for cases of acute flaccid paralysis, a symptom of polio-made real-time tracking of the cases of polio possible and located in the response to vaccination campaigns. To support this surveillance effort, a network of 145 laboratories globally tested for the presence of the poliovirus.³

By 2002, only seven countries were considered polio-endemic. Remaining challenges include shoring up funding gaps, raising vaccination efforts in countries like India, Nigeria, and Pakistan, where transmission remains, and continuous commitment demanded by the complete elimination of the disease.³

Reduction of Poliovirus Incidence Worldwide

Global efforts against polio through vaccination programs have drastically reduced the incidence of the disease since vaccines were introduced in the 1950s. Before widespread vaccination, polio caused widespread paralysis and death, especially in children. In 1988, the Global Polio Eradication Initiative implemented wide-scale vaccination campaigns across 105 countries with high transmission rates.⁴

Therefore, the worldwide prevalence of polio has decreased by over 99% due to these initiatives.The eradication of wild poliovirus types 2 and 3 has been officially certified, while wild poliovirus type 1 has been confined to a minimum residual number of areas in only two countries, namely Pakistan and Afghanistan. The vaccine-derived polioviruses continue to complicate the final stages of eradication in some areas.⁴

By the end of 2021, it was estimated that more than 24 million cases of polio paralysis have been prevented by polio vaccines since 1988. These and many other achievements show the central role that vaccines have played in public health. The battle against polio is ongoing, but global vaccination efforts have made a significant impact by reducing cases and improving disease monitoring and response.⁴

Challenges to Complete Polio Eradication

Despite the tremendous gain, polio eradication still has daunting challenges. Since the start of the GPEI in 1988, polio cases have dropped by more than 99%, and two of the three wild poliovirus serotypes have been eradicated. However, type 1 WPV has continued to persist in the two remaining countries, Afghanistan and Pakistan, where continuous conflicts, insecurity, and mistrust of the vaccine serve as obstacles to immunisation campaigns. These remain hotspots of transmission, and reaching such populations is absolutely essential for the completion of global eradication efforts.⁵

A new challenge that has emerged is the presence of vaccine-derived polioviruses. These emerge when the virus that has been weakened in the oral polio vaccine mutates back to a form that can once more spread and cause outbreaks in the community due to low vaccine coverage. This resulted in the uniform global shift from trivalent OPV-containing protection against all three types of poliovirus to bivalent OPV-containing protection against types 1 and 3 only-in 2016 as a plan to minimise the risk of Vaccine Associated Paralytic-Polio (VAPP). This, however, has eventually produced immunity gaps to type 2 poliovirus, resulting in outbreaks due to cVDPV2, especially in sub-Saharan Africa and Asia.⁵

Efforts to combat these challenges include developing more genetically stable vaccines, such as a novel type 2 OPV (nOPV2), enhancing surveillance systems, and improving vaccine access in conflict zones. The COVID-19 pandemic has further complicated eradication efforts by disrupting vaccination campaigns and straining healthcare resources. To overcome these barriers, global coordination, innovative vaccine solutions, and intensified outreach to hard-to-reach populations are essential for the final push toward a polio-free world.⁵

Impact of Global Vaccination Beyond Polio Reduction

The worldwide vaccination campaign has prevented an estimated 154 million deaths over the past 50 years, making it one of the most successful public health initiatives in history. Vaccines against 14 major diseases - including polio, measles, diphtheria, and tetanus - have significantly reduced infant mortality. Measles vaccination accounted for 94 million of those lives saved, representing one of the most impressive vaccine feats of all time. Global vaccination efforts against poliomyelitis have saved more than 20 million people from being crippled by the disease, thereby bringing the world to the edge of the eradication of polio.⁶

The Expanded Programme on Immunization (EPI) was launched in 1974, and it massively expanded vaccine access, with global immunisation coverage increasing from 5% to 84%. Because of the organisations involved in vaccine development, vaccines have become more accessible to the most underserved communities in the world by ensuring even the most inaccessible populations have access to this important health resource. These combined efforts have helped cut mortality rates in children by more than 50% in some regions-in fact, largely in Africa.⁶

Beyond saving lives, vaccines have contributed to healthier and longer lives, adding an estimated 10.2 billion years of good health globally. Looking ahead, new vaccines against diseases such as malaria, COVID-19, and cervical cancer are expected to save millions of additional lives. With sustained investment, collaboration, and innovation, vaccines will remain one of the cornerstones of global health and continue to create better health outcomes for successive generations.⁶

Conclusion

In fact, vaccination efforts around the world have seen global incidence of polio drop closer to eradication. Since the Global Polio Eradication Initiative began in 1988, polio cases have decreased by over 99%, leaving only two countries where the virus is still endemic. This dramatic success is indicative of what can be achieved by firm international action coupled with wide immunisations.

However, challenges persist, including vaccine-derived poliovirus outbreaks, geopolitical conflicts, and vaccine hesitancy. The COVID-19 pandemic has further complicated eradication efforts. Despite these obstacles, the global health community remains committed to achieving a polio-free world.

Outbreaks of vaccine-derived polioviruses, geopolitical conflicts, and vaccine hesitancy continue to pose obstacles. The COVID-19 pandemic has also complicated eradication efforts. Despite these difficulties, the global health community remains dedicated to achieving a world free of polio.

Realisation of this aim will require continued support from governments, organisations, and individuals. Innovative strategies include the formulation of more stable vaccines and strengthening surveillance systems. Now, while standing at the threshold of eradicating this dreaded disease, the time has come for sustained cooperation on the part of the entire globe to invest in vaccination programs so that polio can finally be assigned to the annals of history.