Why you "stave off" a cold

From the Language Corner of the Columbia Journalism Review:

Nowadays, “stave off” means to keep at bay, fight off, or defend against. But in its original, noun form, around 1400, the Oxford English Dictionary says, a “stave” was a thin strip of wood that was curved to make a cask or barrel...
“Staves” was originally the plural of “staff,” a long rod or walking stick. So by extension, many kinds of sticks or rods, including the staffs of a lance or other weapon, were known as “staves.”
By the 1600s, “stave” meant “to drive off or beat with a staff or stave; esp. in to stave off, to beat off,” the OED says. While the original use was meant literally, as in to “stave off” an attack on the castle, possibly using lances or other weapons with “staves,” the common uses today are figurative, as in “staving off” a cold.