One covered book protection for Mae West (4,6)

I believe the answer is:

life jacket

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'mae west' is the definition.
(I've seen this before)

I don't understand how the remainder of the clue works.

(Other definitions for life jacket that I've seen before include "protective coat" , "Buoyancy aid" , "Cover on biography" , "Buoyant belt" , "Mae West" .)

I've seen this clue in the Sydney Morning Herald.

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