My alma matr in Athens, Ohio University, recently had its annual Halloween celebration, and during the off-campus festivities there was an occurance of some rather brutal stabbings.
Apparently a couple of men were accosting a woman and were confronted by two men seeking to come to her defense. One of the aggressors pulled a knife and stabbed one guy in the gut and the other about five times in the legs. As this happened a police officer arrived to investigate. As he closed to assess the situation the man with the knife stabbed him in the chest and then ran.
The police later picked up a few suspects. The officer, the first victim and the girl are expected to make a full recovery, but the guy who got hit multiply in the legs will probebly face the loss of at least one of his legs.
The cop was wearing a bullistics vest, but the kevlar is a fiber weave and not made to stop knives. Blades cut through the fibers faily easily. There are "anti-knife" or "anti-stab" vests, but they offer very little bullistics defence. I guess you can't have it all, but I hear the military has a very very expensive vest that can give a fairly good measure of protection from both.