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Another Strain of Polio Has Been Eliminated

After a 30-year drive, just one variety remains

A decades-long quest to eliminate polio will mark a significant milestone when the Global Commission for the Certification of Poliomyelitis Eradication declares that wild poliovirus type 3—undetected anywhere in the world since 2012—has been eradicated.

The announcement was timed to coincide with World Polio Day on October 24, 2019. The initiative to eliminate polio has recruited an estimated 20 million volunteers and vaccinated more than 2.5 billion children across 200 countries.

Historically, there were three strains of wild poliovirus—type 1, type 2, and type 3. The last case of type 3 was reported in Nigeria seven years ago. Type 2 was eradicated in 1999, leaving only type 1 in existence.

Polio (poliomyelitis) mainly affects children under 5 years of age. One in 200 infections leads to irreversible paralysis. Among those paralyzed, 5% to 10% die when their breathing muscles become immobilized. There is no cure, but there are two safe and effective polio vaccines. Since the world took up the cause of eradicating polio globally in 1988, the global incidence of polio cases has decreased 99%: from 350,000 cases a year to just 33 in 2018.

Several factors have helped bring polio to the brink of extinction. The polio virus causes acute, short-term infections, meaning that a person infected with polio can normally transmit the virus for only one or two weeks—and it is typically spread only through human waste. The wild poliovirus cannot survive for long periods outside of the human body, so if it cannot find an unvaccinated person to infect, it will die out.

Still, as long as a single child remains infected, children in all countries are at risk of contracting polio. Failure to eradicate polio from these last remaining strongholds could result in as many as 200 000 new cases every year, within 10 years, all over the world.

Sources: Global Polio Eradication Initiative (GPEI) announcement, October 14, 2019; GPEI background, August 19, 2019; WHO, July 22, 2019

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