Fig. 4.

The schematic mechanism of action of vaccine candidates to elicit an immune response against SARS-CoV-2. Different types of vaccines including DNA, RNA, protein, inactivated virus, live-attenuated virus, and vector-based vaccines inter inside the body to elicit the humoral and immune response against viruses. After the entry of the vaccine inside the human body, they enter into the human cell (sky color), where the translation of viral RNA occurs to produce more viral genome copies. In the next step, the specialized cells called antigen-presenting cells (APCs; orange) ingested the virus and activates the T-helper cells (grey) by binding through the virus peptides (imperial purple). The T-helper cells activate the cytotoxic T-cell (grey) and B-cell (light pink). The B-cells produced the antibodies (orange) which blocked the virus and marked the virus for destruction, similarly, cytotoxic T-cell destroys the virus-infected cells. Finally, the T-cells and B-cells remembred the invading pathogens for long-terms to provide a strong immune response [53]. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)