Two young women burst through the door of a health center in a Pakistani slum. One woman sobs. The other tries to explain what just happened.
Nida, 21, and Sahar, 19, are front-line vaccinators — a small but essential role in Pakistan's enormous effort to eradicate the virus. They were going down alleys knocking door-to-door, administering polio vaccine drops to children, when a man pulled out a gun, slammed Nida over the head, snatched her bag and ran away. (Nida and Sahar asked that their last names not be used to protect their safety.)