Polio is a highly infectious disease, mostly affecting young children, that attacks the nervous system and can lead to spinal and respiratory paralysis, and in some cases death.

Polio has existed since prehistoric times – ancient Egyptian images show children walking with canes, with withered limbs characteristic of the disease. 

While it affected children around the world for millennia, the first known clinical description of polio, by British doctor Michael Underwood, was not until 1789, and it was formally recognized as a condition in 1840 by German physician Jakob Heine.

In the late 19th and early 20th centuries, frequent epidemics saw polio become the most feared disease in the world. A major outbreak in New York City in 1916 killed over 2000 people, and the worst recorded US outbreak in 1952 killed over 3000. 

Many who survived the disease faced lifelong consequences. Deformed limbs meant they needed leg braces, crutches or wheelchairs, and some needed to use breathing devices like the iron lung, an artificial respirator invented for treatment of polio patients. 

By the mid-20th century, the poliovirus could be found all over the world and killed or paralysed over half a million people every year. With no cure, and epidemics on the rise, there was an urgent need for a vaccine.

A breakthrough occurred in 1949, when poliovirus was successfully cultivated in human tissue by John Enders, Thomas Weller and Frederick Robbins at Boston Children’s Hospital. Their pioneering work was recognized with the 1954 Nobel Prize.

Not long afterwards, in the early 1950s, the first successful vaccine was created by US physician Jonas Salk. Salk tested his experimental killed-virus vaccine on himself and his family in 1953, and a year later on 1.6 million children in Canada, Finland and the USA. 

The results were announced on 12 April 1955, and Salk’s inactivated polio vaccine (IPV) was licensed on the same day. By 1957, annual cases dropped from 58 000 to 5600, and by 1961, only 161 cases remained. 

Salk was committed to equitable access to his vaccine, and understood that elimination efforts would not work without universal low- or no-cost vaccination.

Six pharmaceutical companies were licensed to produce IPV, and Salk did not profit from sharing the formulation or production processes.

In a 1955 interview, when asked who owned the patent for IPV, he replied: “Well, the people, I would say. There is no patent. Could you patent the sun?”

A second type of polio vaccine, the oral polio vaccine (OPV) was developed by physician and microbiologist Albert Sabin.

Sabin’s vaccine was live-attenuated (using the virus in weakened form) and could be given orally, as drops or on a sugar cube. 

With the Salk vaccine in wide use by the late 1950s, United States interest in testing this new kind of vaccine was low.

Hilary Koprowski had carried out the first test of a live-attenuated vaccine on humans in 1950, and further trials took place in what was then the Belgian Congo (a territory now largely covered by the Democratic Republic of the Congo).

Like Salk, Sabin tested his experimental vaccine on himself and his family; but he had to go further afield for larger-scale trials. 

After a team of Russian virologists visited his lab in 1956, Sabin travelled to Leningrad and Moscow to work with them later that year.

He struck up a longstanding collaboration with Mikhail P Chumakov, who was also responsible for tests of the Salk vaccine in the Soviet Union, and Chumakov carried out initial tests of the live-attenuated vaccine using a seed virus that Sabin had provided. 

Trials carried out in the Soviet Union, on 20 000 children in 1958 and 10 million children in 1959, and in Czechoslovakia, on over 110 000 children from 1958 to 1959, proved the vaccine was safe and effective. 

Independent review of the trials for the World Health Organization by United States specialist Dorothy Horstmann endorsed their findings – a crucial validation in the time of the Cold War.

The ease of administering the oral vaccine made it the ideal candidate for mass vaccination campaigns. Hungary began to use it in December 1959 and Czechoslovakia in early 1960, becoming the first country in the world to eliminate polio.

In 1962, Cuba began to administer the OPV in nationwide immunization programmes. OPV had an added benefit that paved the road to eradication. While IPV protected the vaccinated child, it did not stop the poliovirus from spreading between children. 

OPV, on the other hand, interrupted the chain of transmission, meaning that this was a powerful vaccine to stop polio outbreaks in their tracks.

In 1979 Rotary International started a multi-year project to immunize 6 million children in the Philippines.  

In 1988, the World Health Assembly passed a resolution to eradicate polio – to achieve its permanent reduction to zero, with no risk of reintroduction –  and in the same year, the Global Polio Eradication Initiative (GPEI) was launched. 

The Assembly’s work towards this milestone was complemented by the efforts of Rotary International, who wanted to keep the momentum of smallpox eradication going to ensure that no child was unnecessarily paralysed for life ever again.

Immense contributions by individual countries were combined with international initiative and assistance, with WHO working to support the global collaboration.

With WHO’s assistance, vaccine production was also expanded globally, with significant capacity developed in countries including India and Indonesia.  In 1995, mass vaccination campaigns took place in China and India.

National Immunization Days were coordinated in 19 European and Mediterranean countries in 1995, and in 23 African countries in 2004. By 1994, polio had been eliminated from the Americas, and by 2000 the Western Pacific was polio free. 

By 2003, polio remained endemic in only 6 countries – and by 2006, that number had dropped to 4. 

The 21st century saw further advances, with cases brought down by more than 99% worldwide in less than 2 decades.

WHO’s South-East Asia region was certified polio-free in 2014, the African region in 2020, and the Eastern Mediterranean region has restricted the virus’s reach to just a handful of districts. 

As at July 2021, only 2 cases of wild poliovirus have been recorded globally this year to date: one each in Afghanistan and Pakistan.

But alongside the success of the OPV comes a disadvantage: continued use of the vaccine poses a risk to wiping out the disease.

While OPV is safe and effective, in areas where vaccination coverage is low, the weakened vaccine virus originally contained in OPV can begin to circulate in undervaccinated communities. 

When this happens, if it is allowed to circulate for sufficiently long enough time, it may genetically revert to a ‘strong’ virus, able to cause paralysis, resulting in what is known as circulating vaccine-derived polioviruses (cVDPVs).

If a population is adequately immunized, it will be protected against both wild and vaccine-derived polioviruses. 

Watch this short video and learn how different strains of the polio viruses emerge and how to stop them.