Tom Clarke of Independent Television News narrates this report on the difficult decisions the World Health Organization faces between protecting workers and eradicating a disease.

　　TOM CLARKE:Hundreds turned out to bury Mohammad Hilal, to mourn the loss of a 22-year-old student who gave out polio vaccine in his spare time. But they also came to express public outrage at this week's murders.

　　Nine young people, six of them women, one just 17, have been gunned down since Monday, and not at random, a series of coordinated assassinations targeting an annual three-day polio vaccination campaign.

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　　BUSHRA ARAIN, All Pakistan Lady Health Workers Association (through translator): We go out door to door and risk our lives to save innocent children from being permanently handicapped.

　　For what? So that our coming generations turn out to be healthy. We work for our country, and we are being rewarded in the form of death. What kind of justice is this? Why are we targeted and killed?

　　TOM CLARKE:Until someone claims responsibility, we won't know why. The Taliban haven't come forward, but extreme Islamist groups have long opposed Western health interventions and the role for women in campaigns.

　　Frustration is compounded by the fact they were making such good progress. There were just 56 cases of polio in Pakistan this year, the lowest ever.

　　Up until the 1950s, polio, which can paralyze 10 percent of the children it infects, was one of the world's most feared diseases. Vaccination programs have steadily eradicated it in rich countries, and in recent decades, it's been all but wiped out in the developing world, too.

　　When the World Health Organization launched its campaign 24 years ago, polio was found in more than 125 countries, with around 350,000 cases every year. But now it's endemic in just parts of three countries, Nigeria, Afghanistan, and Pakistan. And the cases have dwindled, 650 last year, and just 213 in 2012 so far.

　　The eradication program has had setbacks before, like a ban linked to extreme Islamists in Nigeria that led to outbreaks in 20 other countries. But observers say this week's violence is something new and requires the WHO to rethink the battle with polio it has so nearly won.

　　DR. HEIDI LARSON, London School of Hygiene and Tropical Medicine: I think it needs to think about how to do it differently, maybe not as polio for polio's sake, but in the context of health.

　　And I know that that's been thought about. I know that the idea of integrating and mixing with other interventions has been thought through, but maybe it needs another look.

　　TOM CLARKE:The WHO warned failure to eliminate polio from its last few strongholds could mean as many as 200,000 new cases every year within a decade. That would be cruel memorial to the young volunteers who were so close to wiping it out for good.