As we near the end of 2013, NPR is taking a look at the numbers that tell the story of this year. Numbers that, if you really understand them, give insight into the world we're living in, right now. Over the next two weeks, you'll hear the stories behind numbers, ranging from zero to 1 trillion.

The lowest number of polio cases ever recorded in the world during one year was 223. And 2013 was on track for an even lower number.

But this was a year when polio pushed back. Hard. The virus reappeared in Somalia and Syria. It showed up in sewer systems in Israel. It spilled out of Nigeria into Cameroon. Pakistan saw a spike in cases.

Even so, global health officials are still confident that polio can be eradicated soon.

The Setbacks

Yes, there were disappointments in 2013, says Sona Bari, a spokeswoman with the World Health Organization in Geneva.

"If you look just at the number of cases, of course, we have a large rise in cases over 2012 to 2013 — more than a 70-percent rise in cases," Bari says. "We have eight countries reporting polio, as opposed to four last year at this time."

Polio had hit a historical low in 2012 with only 223 cases reported worldwide. New outbreaks this year in the Horn of Africa and Syria surpassed that all by themselves.

So how much of a setback is this to the decades-long, multibillion-dollar polio eradication effort?

"I think it's a huge setback when your child has been paralyzed for life," Bari says. "When you live in a country like Somalia or Syria, where possibly you're in a conflict-affected situation, this is the last thing you need. This is the last thing any parent needs."

The outbreaks in Somalia and Syria are "unfortunate spillovers," Bari says, from the three countries where polio transmission has never been stopped: Afghanistan, Pakistan and Nigeria.

There was some progress in these places this year. The number of cases in both Afghanistan and Nigeria fell significantly.

Pakistan, on the other hand, saw things go in the opposite direction. In addition, militants have made it impossible for vaccinators to immunize children in the tribal areas in the north of the country.

The Accomplishments

Despite the overall rise in polio cases this year, Bari says there's been progress on several fronts. "For the first time in history, we have only one type of polio. All these cases are polio type 1. And this has never happened before," she says. "We haven't seen type 3 in more than a year now."

Not to get too technical, but there are three strains of the poliovirus, each requiring a different vaccine. Type 2 was last seen in 1999. This year, type 3 dropped off the map, leaving just type 1 polio for public health officials to contend with.

Polio eradication is finally within reach, says Michael Klag, dean of the Johns Hopkins Bloomberg School of Public Health. "If you look at where we are, it's incredible what we've accomplished. And we're almost there. We cannot stop now," he says.

If polio is wiped out, it would be only the second human disease ever eradicated. The first was smallpox, officially eradicated in 1980.

"We know that at the very end of any campaign like this, the last few countries, the last few cases are always much, much harder than the preceding 80 or 90 percent," Klag says.

Money Well Spent?

So far, billions of dollars have been spent in the eradication drive. The expectation is that it will take billions more to stomp out the last few cases and ensure that polio doesn't stage a comeback. The challenge now is to sustain the political will for such a massive global campaign all the way to the end.

But not everybody agrees that eradication is worth the cost.

Last year, William Muraskin, a health policy researcher at City University of New York, came out with a book called Polio Eradication and Its Discontents. He calls the whole polio eradication movement a failure driven by the egos of Western health officials — consuming resources that could be better used elsewhere.

Muraskin argues that the world would be better off trying to contain polio at low levels and focusing on other, simpler health challenges.

"Putting money into routine immunization systems, that's not attractive," he says. "That's boring. No one is going to get a statue built for strengthening routine immunization systems."

So far, Muraskin is an outlier in a sea of voices pushing to stamp out polio once and for all. Polio eradication campaigns, however, do sap scarce resources in places like Nigeria and Pakistan. And if the polio eradication effort drags on indefinitely, more critics of the strategy are likely to come forward.

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