The world is incredibly close to wiping out polio. This year the number of polio cases has shrunk to fewer than a dozen. And those cases are in just two countries — Afghanistan and Pakistan.

"We are definitely encouraged by the decline in number of cases," says Dr. Rana Safdar, the national coordinator for polio eradication in Pakistan. His country has seen the number of reported polio cases drop from more than 300 in 2014 to just 5 so far in 2017.

"We hope to completely eliminate transmission during the current low transmission season, which starts from September and ends in May," he says. "We are very confident we can do this. But the last mile is always very difficult."

Pakistan has been holding national polio immunization days in which a quarter of a million vaccinators attempt to make sure 38 million children get all three doses of the oral polio vaccine.

"We must reach these children from the coast of Karachi to the mountains in the highest part of Pakistan," Dr. Rana says.

If polio transmission is stopped in Pakistan and neighboring Afghanistan, it would be a major milestone in public health. Assuming the virus doesn't manage to take root elsewhere, polio would be only the second human disease to be eradicated after smallpox. And virologists say smallpox was a far easier target than polio. With smallpox if someone was infectious they were also visibly ill. Polio on the other hand can be spread by people who show no signs of being sick. The polio virus can also hide in and spread through sewage. With smallpox, officials just needed to contain the virus at the sick patients' beds. Polio is far more wily.

A global plan to eradicate polio launched in 1988 set an eradication date of the year 2000. The program made incredible progress, dropping the number of cases year from more than 300,000 worldwide to just 11 today. But the eradication program has cost billions of dollars and has struggled to deal the virus a decisive fatal blow. In 2014 Africa appeared to be polio free only to have the paralytic disease pop back up in Nigeria two years later. The last case reported in Africa (or for that matter anywhere other than in Pakistan or Afghanistan) was in more than a year ago in Nigeria. Cases of vaccine-derived polio have re-emerged in Syria and other conflict zones. As long as the live vaccine is still being used, the potential for vaccine-derived cases remain. These cases stem from strains of the oral vaccine that have mutated and regained strength in the environment. But the plan is to stop using the live, oral vaccine as soon as wild polio is wiped out. At that point the whole world would exclusively be using an injectable vaccine that doesn't contain live virus.

Dr. Rana in Pakistan is confident that that day is coming soon. Polio, he says, is in its last days and will soon be wiped out.

"We are sure we will meet our goal very soon," he says.

Originally Pakistan had set that goal as 2016. Earlier the Global Polio Eradication Initiative had set the year 2000 as the target for polio's demise. Despite those missed deadlines, the number of polio cases globally is at an all-time low and the world appears closer to being polio-free than ever before.

On Friday, NPR and The Forum at the Harvard T.H. Chan School of Public Health presented a discussion with polio experts: "Eradicating Polio: Reaching the Last Child."

The panelists talked about how the world has come so close to this "last mile" of polio eradication and what steps need to be taken to end transmission.

The discussion was livestreamed on our website Friday at 11 a.m. ET and is archived here.

Jason Beaubien, global health correspondent for NPR, moderated the discussion with:

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