New polio vaccines are key to preventing outbreaks and achieving eradication

We’ve come a long way in the fight against polio — the infectious disease that used to paralyze hundreds of thousands of people each year. Most of them were children. Eradication is possible, but the last stretch has proven difficult.

Two of the three serotypes (distinct types within a species of virus) of wild poliovirus have already been eradicated.

However, two big challenges remain in crossing the finish line. One is eliminating the last serotype of wild poliovirus. Another is containing vaccine-derived polioviruses, which arose from oral polio vaccines in rare circumstances and spread in some regions where protection against the disease declined.

The world can overcome these hurdles. We can use new vaccines to contain them and improve testing, outbreak responses, and sanitation.

The chart below shows the dramatic decline in polio cases.

This was possible due to effective vaccination efforts with two types of vaccine: inactivated polio vaccines (IPV), developed by Jonas Salk in 1955, and oral polio vaccines (OPV), developed by Albert Sabin in 1961.

Improvements in providing clean water and sanitation have also helped to reduce the spread of poliovirus through contaminated water and food and the risks of other infections, which prevent children from developing immunity against polio.¹

In the early 1980s, there were around 400,000 estimated cases annually. In the last few years, there have been around 4,000. That’s a hundred-fold decline. Millions of children have been spared lifelong paralysis.

Wild poliovirus has three serotypes. The three serotypes are distinct types of poliovirus with protein structures that differ sufficiently that protection from one doesn’t protect from the other.

The world has eradicated wild poliovirus serotypes 2 and 3.²

• The last case of wild poliovirus serotype 2 was in 1999 in India, and the WHO declared it eradicated in 2015.
• The last case of wild poliovirus serotype 3 was seen in 2012 in Nigeria, and it was declared eradicated in 2019.³

The world is, therefore, very close to eradicating all serotypes of wild poliovirus globally.

As shown in the map below, only two countries — Afghanistan and Pakistan — are still endemic for wild poliovirus serotype 1 (WPV1).

But as the chart shows, the number of cases is now very low. In 2023, only six cases of wild polio were reported in Afghanistan and another six in Pakistan.

By testing widely to identify potential cases, working with local communities in hard-to-reach areas and at borders, and improving vaccination rates and sanitation, this goal is within reach.⁴

Although the absolute number of cases is much lower than in the past, most cases recently have come from vaccine-derived polioviruses (VDPVs), as shown in the chart below.⁵

Vaccine-derived polioviruses can arise from the weakened virus in the oral polio vaccine if it has mutated significantly over time in vaccinated people and reverted to the original strain of polio.

Oral polio vaccines are used in poorer countries because they are much easier to administer (as oral drops) and cheaper to manufacture than inactivated polio vaccines, which must be given by injection.⁶

People with immune deficiencies are at higher risk of the vaccine reverting because they can sustain longer infections, giving the virus more time to evolve.⁷

It can then spread and cause new outbreaks if immunity has fallen in communities. So, somewhat counterintuitively, communities with lower vaccination coverage are more vulnerable to vaccine-derived polio.⁸

So far, most cases of vaccine-derived poliovirus have come from vaccine-derived polioviruses of serotype 2 — known as VDPV2 — which can mutate faster than other serotypes, making it more likely to revert than other serotypes.⁹

In addition, there were interruptions in vaccination against polio serotype 2 in 2016, when vaccination against that particular serotype was switched from the oral to the inactivated polio vaccine. It was harder to provide inactivated polio vaccines at scale in poorer regions and reach every child, leading to a rise in cases.¹⁰

Since 2021, new oral polio vaccines against serotype 2 have been used to prevent further outbreaks of VDPV2.

These are much more genetically stable than the previous oral polio vaccine and much less likely to mutate or potentially revert to the original strain.¹¹

They have already been rolled out widely and helped effectively control outbreaks of VDPV2.¹²

New oral polio vaccines against serotypes 1 and 3 are still in development.¹³

In addition, new types of inactivated polio vaccines are also being developed. For example, some candidate vaccines can be administered through skin patches instead of injections. These could be cheaper, easier to provide, and unable to revert to the original strain.¹⁴

These new technologies will be crucial in preventing further outbreaks as we approach the ultimate goal of polio eradication.

To achieve polio eradication, it’s crucial to contain every last case quickly to prevent the spread of polio and protect children from this debilitating disease.

We can use new vaccines, increase polio testing, and improve access to clean water and sanitation.

Together, we can successfully close the chapter on polio, which would be a major victory for humanity.

Saloni Dattani (2024) - “New polio vaccines are key to preventing outbreaks and achieving eradication” Published online at OurWorldInData.org. Retrieved from: 'https://ourworldindata.org/new-polio-vaccines-are-key-to-preventing-outbreaks-and-achieving-eradication' [Online Resource]

@article{owid-new-polio-vaccines-are-key-to-preventing-outbreaks-and-achieving-eradication,
    author = {Saloni Dattani},
    title = {New polio vaccines are key to preventing outbreaks and achieving eradication},
    journal = {Our World in Data},
    year = {2024},
    note = {https://ourworldindata.org/new-polio-vaccines-are-key-to-preventing-outbreaks-and-achieving-eradication}
}