In a paper entitled "Progress and Prospects on Vaccine Development against SARS-CoV-2", the authors write the following in section 2.5:
"Compared with S, N, and M protein, E protein is not suitable for use as an immunogen. For one reason, it consists of 76–109 amino acids in different coronaviruses with channel activity, thus the immunogenicity is limited. Studies have shown that SARS-CoV E protein is an important virulence factor, and the secretion of inflammatory factors IL-1β, TNF, and IL-6 are significantly reduced after knocking out E protein"
Why does the fact it consists of 76–109 amino acids in different coronaviruses with channel activity imply its immunogenicity would be limited?