influenza vs contagious disease

influenza and contagious disease both are nouns.

Word	Noun	Adjective	Verb	Adverb
influenza	Yes	No	No	No
contagious disease	Yes	No	No	No

As nouns, contagious disease is a hypernym of influenza; that is, contagious disease is a word with a broader meaning than influenza:

Other hypernyms of influenza include contagion, respiratory disease, respiratory disorder, respiratory illness.

influenza (noun)	contagious disease (noun)
an acute febrile highly contagious viral disease	any disease easily transmitted by contact