For millennia, this species made its way into human communities around the world, seeking and finding hospitable places to live. But in 1988, its fortunes changed: a determined group of people decided to stop it in its tracks, and it began to die off. Today, it’s nearly gone from the face of the earth.
I'm not talking about endangered animals or plants. The species teetering on the verge of extinction is a debilitating and deadly virus: polio. In this case the extinction will be welcome, marking the end of a devastating disease that can permanently paralyze or kill the young children on which it most frequently preys.
The polio virus can survive in the environment for a time, but it can only reproduce in humans. Since an infected person’s immune system usually gets rid of the virus within 4-8 weeks, the virus needs to find a new human carrier or it will die off. The higher the proportion of immunized and protected children, the harder it is for the virus to find a place to go, and it eventually disappears. We saw this pattern first in individual countries and then on a global scale, and now we are getting close to the finish line.
Polio comes in three different types, or strains, each with its own characteristics. Wild polio virus type 1 is the most likely to travel over large geographic areas and cause outbreaks, paralyzing one in every 200 children it infects. Wild polio virus type 3 is more insidious, traveling silently through populations and paralyzing only one in every 1,000 children it infects.
Wild polio virus type 2 was the first strain we conquered. It last paralyzed a child in 1999, and was officially declared eradicated in September 2015. It looks like WPV3 is next — this month marks three years since we’ve seen it anywhere in the world, either in paralyzed children or in the environment.
This milestone brings us an important step closer to polio eradication — we are now closing in on the last remaining strain, with only 52 cases of WPV1 globally so far in 2015. Many regions that have eliminated polio have done so in this same sequence. For example, India, long considered the most difficult place in the world to end the disease, first eliminated indigenous WPV2 in 1999, then WPV3 in 2010. The remaining strain, WPV1, held on for only one more year and was last seen in 2011. Today, the country has gone almost five years polio-free.
Thanks to more sophisticated technology, today the polio program can look at relationships of viruses beyond just the type, and genetically sequence each new polio virus it finds. This allows us to trace the virus’ exact origin and track how different “families” within each strain spread. We now know that not only are we down to just WPV1, but we have eliminated all but a few WPV1 genetic families.
Strong surveillance systems are one of the key tools for finishing off the job. They find the virus and allow us to measure progress in stopping the different virus types and families, and tell us where the virus is so we can focus vaccination activities to eliminate it.
This year, WPV1 has paralyzed children in only two countries: Afghanistan and Pakistan. Now that WPV2 is eradicated and WPV3 is likely gone as well, eradication efforts can hone in on the last remaining type of polio. Once this last polio virus is gone, countries can begin to repurpose polio health workers and infrastructure to tackle other health issues.
Polio’s shrinking geographic territory and genetic diversity show that eradication — one of the most ambitious public health goals ever pursued — is not only achievable but, with continued high quality immunization campaigns, success is right around the corner.
We’ve already gotten rid of two of the three types of polio virus. To turn polio from endangered to extinct, we need to stay focused. Like any species fighting to survive, it will do whatever it can to bounce back. We know our process works: track the virus, immunize children, and the virus dies. If governments, donors, and millions of health workers keep it up, we will put polio in the history books.
Dr. Jay Wenger leads the Bill & Melinda Gates Foundation’s polio eradication efforts within the Global Development Program. He manages a high-performing team and works across the foundation to drive instrumental advocacy work, resource mobilization, communications, and research and product development. He represents the foundation both internally and externally and helps to shape and execute the polio eradication strategy.
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