Table 1.

Vaccine strategies for swine enteric Coronaviruses.

Vaccine type	Development	Advantages	Disadvantages	Coronavirus antigen
Inactivated virus (Baek et al., 2016, Frederickson et al., 2014, Berube et al., 2015)	Virions are inactivated with chemicals.	Easy to prepare; cannot cause disease if properly inactivated.	Can induce Th2-skewed immune response; needs adjuvant.	Whole virus
Live-attenuated virus (de Arriba et al., 2002, Sato et al., 2011)	Genomes are mutated using multiple passages in Vero cells.	Inexpensive; strong cellular and humoral immune responses; can be given orally.	Reversion to virulence; can still cause some disease; protection is dose dependent.	Whole virus
Viral vectored (Yuan et al., 2015, Tuboly and Nagy, 2001).	Unrelated viral genome (Poxvirus, Adenovirus) engineered to express the gene of interest.	Strong cellular and humoral immune responses; intrinsic adjuvant properties; can be given orally.	Preexisting immunity against vector virus.	Spike protein
Subunit (Oh et al., 2014, Makadiya et al., 2016, Bae et al., 2003)	Antigen is expressed in mammalian, baculovirus, yeast or plant cells.	Cannot cause disease from viral infection; can generate high-titer neutralizing antibodies.	Expensive; needs adjuvant; protection can be incomplete.	Spike protein
DNA vaccines (Zhang et al., 2016b, Meng et al., 2013)	Genes encoding antigens are cloned into plasmid expression vector.	Cannot cause disease from viral infection; can be given orally when introduced into Lactobacillus or Salmonella.	Th1-skewed immune response when used alone.	Spike, nucleocapsid or membrane proteins
Viral replicating particles vaccine (Mogler et al., 2014a, Mogler et al., 2014b)	Replicon RNA containing gene of interest is packaged into alphavirus virion particles.	Cannot cause disease from viral infection; intrinsic adjuvant properties; high level of antigen expression.	Oral delivery has not been demonstrated.	Spike protein