Height of happiness: Getting frontline of employees vaccinated! (9)

I believe the answer is:

elevation

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

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

(Other definitions for elevation that I've seen before include "Height - a live note (anag)" , "Drawing of the external face of a building" , "Height above a given level" , "Side of a building; height" , "High point" .)

I've seen this clue in The Hindu.

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