RENEE MONTAGNE, HOST:

And as we've been reporting this week, Pakistan is one of the last places in the world where children are still getting polio. Vaccine programs face intense and sometimes violent opposition. Of course it's crucial for health workers to convince parents to let their children receive a vaccine for polio, just like it would be in any country. So a team of Harvard researchers recently did a poll to find out if parents in Pakistan are part of the problem. NPR's Nurith Aizenman reports that the results stunned those researchers.

NURITH AIZENMAN, BYLINE: Imagine you're a parent in northwest Pakistan. You live in a remote village - think mud huts on mountaintops - and every few weeks, some strangers carrying vials of an odd liquid come knocking on your door.

SONA BARI: Frankly, if someone came to my house and said, you don't know me from Adam, but I'd like to vaccinate your child, I wouldn't let them.

AIZENMAN: That's Sona Bari of the World Health Organization, a key player in a decades long campaign to stamp out polio. And yet that effort's success depends on these parents in Pakistan saying, yes. The weirdness of strangers showing up at your door isn't the only hurdle. In Pakistan's Northwest tribal areas, where most of the polio cases are found, parents face a lot of pressure to say no. I'm talking about the Taliban.

(SOUNDBITE OF ARCHIVED RECORDING)

CROWD: (Chanting) USA, USA.

UNIDENTIFIED MAN 1: Osama bin Laden is dead.

AIZENMAN: Remember in 2011 when U.S. forces tracked down and killed Osama bin Laden in Pakistan. Well, it soon came out that they had used a vaccination campaign as cover during the hunt. Now, it was for hepatitis not polio. Still, the Taliban was furious. Here's Sherine Guirguis of UNICEF which co-sponsored the poll with Harvard.

SHERINE GUIRGUIS: There have been health worker attacks and there have been bans on polio campaigns for two years now. So there's this climate that we're working in.

AIZENMAN: More than 60 polio workers have been killed. And the Taliban still outright bans vaccinators from two areas where they have a lot control. The result of those bans, a surge in polio in that region, more than 50 kids paralyzed just this year. The message to parents from all this, don't even think of opening your door for a vaccinator. And it's not just the Taliban. Across Pakistan, the revelation about the CIA's ploy created suspicion about what vaccinators are really up to.

UNIDENTIFIED MAN 2: (Sindhi spoken).

AIZENMAN: This is a preacher all the way in the Southwest of Pakistan. He's telling his congregation that polio vaccination program, its run by foreigners who are out to sterilize Muslim children. And UNICEF's Sherine Guirguis said that the pollsters they sent, they found that people have heard a lot of rumors like this.

GUIRGUIS: The vaccine is not halal, for example, or that it's not made with ingredients that they feel comfortable with.

AIZENMAN: Or worse, the vaccine gives your kids AIDS. On the plus side nationwide, only 1 in 10 parents thought the rumors might be true. And even in the Northwest tribal areas, only a third thought there might be something to the tales. But researchers say these rumors can still be a problem. Gillian SteelFisher of Harvard ran the poll.

GILLIAN STEELFISHER: Peopled don't necessarily have to please them in full, but you worry about that kind of atmosphere of misunderstanding about the vaccine.

AIZENMAN: That's because of another challenge facing the polio eradication effort. With other vaccine programs, it's enough to reach a good majority of kids. But when it comes to polio, health workers are trying to wipe this disease off the planet. So UNICEF's Sherine Guirguis says even reaching say 75 percent of kids isn't good enough.

GUIRGUIS: Polio's 100 percent program. You need to find every child living in the most far-flung area, living in the most conflict-affected area, living in the hardest-to-reach area.

AIZENMAN: And you don't just need to reach them once or even twice or even three times; you need to convince parents to let you vaccinate their child at least four times in a single year. That's what it takes to get full immunity with this vaccine. And when you keep showing up, parents might start to get exasperated. Here's the World Health Organization's Sona Bari.

BARI: So this is one of the few services they're seeing come to their door for free, and yet it's coming over and over, which is something that's hard for them to understand.

AIZENMAN: See, polio is a big priority for the international community, but it's become rare enough that in Northwest Pakistan a lot of these parents haven't ever seen it. It's not really on their minds. Harvard's Gillian SteelFisher says they brought up a lot of other concerns.

STEELFISHER: They're facing the most fundamental challenges, things like clean water.

AIZENMAN: SteelFisher's team also found that a lot of parents don't think polio is that serious, that the paralysis it causes is curable - it isn't. And when they ask parents - does your child have to take the vaccine every time it's offered? - a lot of parents said, yes, always.

STEELFISHER: But we also had a sizable share of parents who said, sometimes, not necessarily every time.

AIZENMAN: And yet for all of these obstacles, when the pollsters asked parents in the Northwest tribal areas the central question - the question that was most important to their poll - if a health worker came to your door, did you let them vaccinate your child? - practically every parent 95 percent said yes. Nurith Aizenman, NPR News.