HIV virus vs human immunodeficiency virus

HIV virus

noun
  • Synonym of HIV (“human immunodeficiency virus”) 

human immunodeficiency virus

noun
  • Either of the two related viruses, human immunodeficiency virus 1 (HIV-1) and human immunodeficiency virus 2 (HIV-2) that progressively destroy the body's immune system and can potentially lead to AIDS. 

How often have the words HIV virus and human immunodeficiency virus occurred in a corpus of books? (source: Google Ngram Viewer )