Coronavirus spike protein-based vaccines. Vaccine delivery systems

Spike protein has been established as one of the molecules playing a pivotal role in coronavirus infection. On its bases, several vaccines have been developed, passed preclinical and clinical stages, and reached medical practice at the early stages of the pandemic. It was found efficient enough to induce various types of immunoglobulins. However, the missense mutations made it necessary to develop new sequences with adjuvants to enhance the efficacy against a broad spectrum of SARS-CoV-2 and newly emerging variants. Some attempts were carried out to improve the vaccine efficiency by loading it into a delivery system, which caused a prolongation effect. In this paper, we reviewed data around spike protein-based vaccines in terms of their efficacy, which was analyzed based on enhanced quantities/titers of immunoglobulins/neutralizing antibodies. Our search on the PubMed database using ‘spike protein-based coronavirus vaccines’ keywords showed over 150 publications that were further filtered based on their relevance. Further, we added other relevant papers to support the expressed ideas. We compared the effects of various vaccines of different origins in clinical studies and animal experiments where relevant. The efficacy of adjuvants has been reviewed as a separate section. In several cases, we explained the significance of the spike protein trimeric structure. We also explained the essential role of mutation while developing protein vaccines. The contributions of adjuvants in inducing immune responses have been separated into one section. The outcomes of clinical studies were highlighted to prove their efficacies.