Vaccines overview:
Recently, there have been several attempts to create vaccines against human Corona virus infections, however, all were limited due to their wide diversity of sequences(71). Several vaccines and immunotherapies have been tried during the latest viral epidemics such as Zika, Ebola and the previous CoVs family infections. Most of these trials have been investigated firmly to assess their applicability and usefulness in preventing the current pandemic (72).
Most of the current CoV vaccines attempts are targeting the S protein of the virus as it is the principal promotor of antibodies development and T-cell responses making it the perfect candidate in vaccines development strategies. Examples of these vaccines are involving the full length S protein or other appropriate parts of it or S1 receptor binding domain or virus like particles (VLP) , viral vectors or DNA (71), (73), (74)and (75).
The most efficient vaccine should enhance both the production of blocking antibodies that target the S1 subunit receptor binding domain to block the binding of the S1 protein of the virus to its receptor, in addition to blocking the viral RNA uncoating. Chen et al., has demonstrated that the C-terminal domain of the S1 subunit of porcine Deltacoronavirus  conatins the immunodominant region that evolves the strongest blocking effect(76). Furthermore, because of RBD capability to trigger the formation of neutralizing antibodies, both recombinant peptides containing RBD and recombinant vectors encoding RBD may be promising for the production of successful SARS-CoV vaccines(74).
Kim et al has shown that the nasal administration of recombinant adenovirus-based vaccines that express MERS Spike protein into mice, enhances the production of IgG and secretory IgA antibodies as well as inducing the activation of T lymphocytes and development of memory cells which reside mainly in lungs giving those mice life-long immune response responses(77).
Moreover, a study which compared the effect of rabies virus as a viral vector against Gram-positive enhancer matrix (GEM) as a bacterial vector; both of them expressing MERS Spike protein; they found that the viral vector vaccine gave the mice markedly stronger cell mediated immune response and faster humoral immunity(78). Additionally, knowing that there are much similarities between SARS and MERS, the applicability of designing one vaccine working against all CoV family viruses was investigated and they found that there is possible cross-reactivity among CoVs(79).
Also, since SARS-CoV-2 and SARS exhibit antigenic similarity, vaccines developed against SARS could be cross-reactive against SARS-CoV-2 (80). However, when the sequences of the full-length S protein of SARS-CoV-2 was compared with that of SARS, they found that the most variable regions exist in the S1 subunit of spike protein which is normally the main target of most developed vaccine(81) which may assume the difficulty of designing one common efficient vaccine for both viruses (82).
The nucleocapsid (N) protein and the possible B cell epitopes of MERS E protein have been recommended as feasible targets that could initiate cell mediated and humoral immune interactions(83). In addition,  reverse genetic approaches were applied in live-attenuated vaccines to deactivate the exonuclease effects of non-structural protein 14 (nsp14) or to eliminate the envelope protein in SARS (71). Avian infectious bronchitis virus (IBV) is a chicken Corona virus and it was suggested by Bijlenga that strain H of avian live virus IBV vaccine might be helpful in protecting against SARS (84). Since this vaccine is depending mainly on the production of neutralizing antibodies, so it may be suggested as another effective choice for protection against SARS-CoV-2 after assessing its efficacy in monkeys(85).
Rocky Mountain Laboratories are cooperating with Oxford University to grow an adenovirus vector vaccine against SARS-CoV-2 to be tried in chimpanzees first. In addition, another study is investigating clinical trials for a new vaccine expressing SARS-CoV-2 S protein in the mRNA vaccine platform technology (86). Lately, the Coalition for Epidemic Preparedness Innovations (CEPI) declared the launch of three plans designed to produce SARS-CoV-2 vaccines using already existing vaccines’ platforms. These platform work through the synthesis of viral surface proteins which bind to the host cell membrane and clamp the cells into shape. This could enhance better and faster detection of viral antigens by the host immunity(87).