booster shot vs dosage

booster shot and dosage both are nouns.

Word	Noun	Adjective	Verb	Adverb
booster shot	Yes	No	No	No
dosage	Yes	No	No	No

As nouns, dosage is a hypernym of booster shot; that is, dosage is a word with a broader meaning than booster shot:

booster shot: an additional dose that makes sure the first dose was effective
dosage: a measured portion of medicine taken at any one time

Other hypernyms of booster shot include dose.

booster shot (noun)	dosage (noun)
an additional dose that makes sure the first dose was effective	a measured portion of medicine taken at any one time
	the quantity of an active agent (substance or radiation) taken in or absorbed at any one time