I was denied exit from PVG about 2 years ago because I had a fever. Actually, the scanner let me pass, but I told the screening agent that I wasn't feeling well and they rejected my quarantine form. This exempted me from a $150 change fee, though I really wish I hadn't had to go all the way out to the airport to plead my case (I showed up in the NW office with the same fever a day earlier and they gave me no love.)