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Global health officials will on Thursday announce a partial victory in the decades-long fight to end polio, with a second of three strains of the crippling virus certified as eradicated worldwide.

The ending of wild polio virus type 3 – also known as WPV3 – will be the third human disease-causing pathogen to be eradicated in history, after smallpox was declared wiped out in 1980 and wild polio virus type 2 (WPV2) in 2015.

Polio spreads in vulnerable populations in areas where there is no immunity and sanitation is poor. It invades the nervous system and can cause irreversible paralysis within hours.

It cannot be cured, but infection can be prevented by vaccination – and a dramatic reduction in case numbers worldwide in recent decades has been largely due to intense national and regional immunisation campaigns in babies and children.

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The last case of polio type 3 was detected in northern Nigeria in 2012, and global health officials have since been conducting intense surveillance to ensure it has gone.

“With no wild poliovirus type 3 detected anywhere in the world since 2012, the Global Commission for the Certification of Poliomyelitis Eradication is anticipated to officially declare this strain as globally eradicated,” the Global Polio Eradication Initiative (GPEI) said in a statement.

The success in ending type 3 means that only type 1 of the wild virus is still circulating and causing infections.

3:52 How Lakefield, Ont., contributed to the global fight against polio How Lakefield, Ont., contributed to the global fight against polio

Polio type 1 is endemic in two countries – Afghanistan and Pakistan – but efforts to wipe it out have faced setbacks in the past two years.

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After reaching a historic low of only 22 cases of wild polio infection in 2017, the virus has caused 72 cases in Pakistan and Afghanistan already this year – pushing back yet further the potential date for the world to wipe polio out altogether.

The first target date for ending polio was set in 1988 by the GPEI, a partnership of the World Health Organization, the health charity Rotary International and others, which had aimed to eradicate it by 2000.

GPEI said, however, that this week’s declaration of the end of WPV3 was a “significant milestone”, while Carol Pandak, director of Rotary’s PolioPlus program, said it proves that a polio-free world is achievable. “Even as the polio program addresses major challenges, we’re making important headway in other areas,” she said.