4.1 Whole Cell Antigen
The elements of virus particles, including proteins, lipids,
polysaccharides, nucleic acids, and other associated components,
constitute whole cell antigens (WCA) (Zhang et al., 2020). The
development of killed and live-attenuated vaccines present the whole
cell antigens to elicit immune response (Minor et al., 2015). In this
regard virus strains of SARS-CoV-2 have been successfully isolated by
many institutions globally for development of killed or live-attenuated
whole cell vaccine (Zhang et al., 2020). However, it is unavoidable to
face more difficulties in quality control and consistency evaluation of
such vaccines because of complex compositions antigens and such vaccines
require stringent screening and testing for obtaining strains with
certified safety (Marohn and Barry, 2013). For example, a mutation
(Y6398H) has been introduced into the Orf1a/b polyprotein
(p59/nsp14/ExoN) which completely attenuated the virulence of mouse
coronavirus (MHV-A59) and MHV-A59 vaccine significantly reduced virus
replication in mice at day five following intracerebral inoculation
(Morse et al., 2020).