After Killings, U.N. Stops Vaccine Work in Pakistan Listen Download Embed Share Share this on Facebook (Opens in a new window) Share this on Twitter (Opens in a new window) Share this via Email Pakistani polio vaccination workers shout slogans against the killing of their colleagues during a protest in Karachi on December 19, 2012. ( Rizwan Tabassum / Getty ) Produced by PRI and WNYC