We see in Harry Potter and the Order of the Phoenix that McGonagall has her Transfiguration students practice the Vanishing Charm (Evanesco) on mice (and has previously had them do snails):
“As I was saying, the Vanishing Spell becomes more difficult with the complexity of the animal to be vanished. The snail, as an invertebrate, does not present much of a challenge; the mouse, as a mammal, offers a much greater one. This is not, therefore, magic you can accomplish with your mind on your dinner. So — you know the incantation, let me see what you can do. . . .”
Harry Potter and the Order of the Phoenix
...and Ron manages to vanish most of his mouse:
“Well, it’s a start,” said Ron, holding up a long, wriggling mouse tail and dropping it back into the box Lavender was passing around.
Harry Potter and the Order of the Phoenix
This raises the question of is it possible to Vanish humans? We've seen that mammals (such as our friendly, little mouse) are not exempt from being Vanished. Does this hold true for humans?