**4. Immunological responses to different type of COVID-19 vaccines**

**Inactivated vaccine:** the genetic material is inactivated or destroyed in inactivated vaccine which after ingested by antigen presenting cell stimulate the helper T cells which in order stimulate B-cell to produce antibodies as described in **Figure 1** [7]. **Example: COVAXIN (Bharat Biotech).**

**Figure 1.** *Inactivated vaccine.*

#### *COVID-19 Vaccine: A Way Out of Crisis DOI: http://dx.doi.org/10.5772/intechopen.98736*

**Subunit Vaccine:** In this vaccine only a part of the agent imitates like real infection and stimulate helper T cells which in turn stimulates B cells to produce antibodies as described in **Figure 2**.

**Example: Novavax (protein subunit).**

**Viral vector Vaccine:** these vaccines use non-coronavirus vector modified to carry gene coding for the SARS-COV-2 antigen. This antigen gets expressed on the cells infected gets ingested by antigen presenting cell which then project the complex to helper T cells which then activates both the B-Cells and Cytotoxic T cell as described in **Figure 3**.

**Example: AstraZeneca-oxford vaccine and Sputnik-V (Gamaleya Research Institute).**

**Figure 3.** *Viral vector vaccine.*

**RNA Vaccine:** RNA vaccines are antigen-coding strands of messenger RNA (mRNA) delivered inside a lipid coat. Once inside cells, the mRNA is translated into the protein antigen, which is secreted. The antigen is recognized, inducing an immune reaction. It induces T-helper and cytotoxic T-cells, and antibodies. mRNA also recognized by cells as 'pathogen' stimulating strong immune response as described in **Figure 4**.

**Example: Pfizer/BioNTech and Moderna vaccine.**
