4.5 Envelop protein (E)
The E protein is the smallest of the major structural proteins of CoVs. It is an important virulence factor and its knocking out has shown marked reduction of inflammatory factors IL-1β, TNF, and IL-6 (Nieto-Torres et al., 2014). The potential B cell epitopes of the E protein of MERS-CoV are considered as probable vaccine protective targets which have the capacity to induce both T-cell and neutralizing antibody responses (Shi et al., 2015; Xie et al., 2018). However, its immunogenicity is quite limited compared to other structural proteins (Zhang et al., 2020) and has been least investigated for vaccine development due to which it cannot considered as a suitable vaccine candidate for COVID-19.