It has mostly got to do with health workers who were at risk because the clerics and Taliban threatened them. They also spread the misinformation that vaccinations are a Western conspiracy against Pakistanis to sterilise and reduce the population of Muslims.
http://www.theguardian.com/commentisfree/belief/2011/nov/04/...
Sadly, most people in these areas are uneducated and they believe what the clerics tell them. The health workers were literally risking their lives.