The world is closer than ever to being able to wipe out polio, international experts said on Thursday, with zero cases of the crippling disease recorded across all of Africa this year and fewer than 25 globally.

Polio eradication specialists are wary of claiming premature success and warn complacency could prove the project's downfall, but with only two countries, Pakistan and Afghanistan, reporting polio cases in 2015, they see an end in sight.

"We've never been in a better place to hold hopes of being able to eradicate this disease once and for all," said Peter Crowley of the United Nations children's fund UNICEF.

Jay Wenger, head of polio eradication at the Gates Foundation, told reporters: "The progress is very impressive. We're looking forward to finishing the job."

"We don't think we can declare victory, but we've never gone anywhere near this long without any wild polio virus being found in Nigeria or in Africa as a whole," he said on a telephone briefing with experts from the World Health Organization (WHO), the Global Polio Eradication Initiative (GPEI) and the U.S. Centres of Disease Prevention and Control.

Polio is a viral disease that invades the nervous system and can cause irreversible paralysis within hours. It can spread rapidly, particularly among children and especially in unsanitary conditions in war-torn regions, refugee camps and areas where healthcare is limited.

In 1988, when the GPEI was formed to lead a battle to wipe it out, polio was endemic in 125 countries and paralyzed nearly 1,000 children a day. Since then, thanks to huge vaccination campaigns, there has been a more than 99 percent global reduction in cases.

But the WHO's repeated warning is that as long as any child anywhere remains infected with polio, all children are at risk.

Latest global data show just 23 polio cases reported so far in 2015 -- 22 in Pakistan and one in Afghanistan. That compares to a year-to-date total of 54 cases worldwide in 2014, and a 2014 annual count of 306.

Wenger said the success in Nigeria, which has not seen a single polio case for eight months, was largely due to political will from national, regional and local government.

The experts said progress against polio remains fragile, particularly since it is in regions vulnerable to instability. In 2013, polio re-emerged in Syria after a 14-year absence, prompting a vast and expensive regional vaccination campaign.