"The capsid faces may consist of one or more proteins."
https://en.wikipedia.org/wiki/Capsid
"The capsid encloses the genetic material of the virus"
https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Book%3A_Introductory_Biology_(CK-12)/07%3A_Prokaryotes_and_Viruses/7.08%3A_Virus_Structures
"A peptide antigen is the use of a peptide to trigger an animal's immune system to develop antibodies to that peptide. Peptides are short strings of amino acids;"
https://www.wise-geek.com/what-is-a-peptide-antigen.htm
"However, often the antigen to which the immune system responds is a relatively small number of amino acids or peptide."
https://www.who.int/biologicals/vaccines/synthetic_peptide_vaccines/en/