Table 1.

Types and Details of Some COVID-19 Vaccines.

Vaccine	Immunological action
1- Pfizer-BioNTech	The vaccine is composed of lipid particles that encourage the RNA delivery to host cells and allow the SARS-CoV-2 S antigen expression. It protects the body against the COVID-19 by promoting an immune response to the S antigen. (Dong et al., 2020, Anderson et al., 2020)
2- Moderna	The nucleoside-modified mRNA vaccine is produced in the form of lipid particles. It allows the nucleoside-modified mRNA and SARS-CoV-2 to be delivered and expressed, respectively. The vaccine stimulates an immune response to the S antigen, thus protecting against the COVID-19. The antibodies are unique to the SARS-CoV-2 virus that help defend against potential infection. (Dong et al., 2020, Anderson et al., 2020)
3- Johnson & Johnson’s Janssen	The vaccine developed by Johnson & Johnson employs viral vector technology. Adenovirus 26 is a common cold virus that has been genetically modified to infect cells but not replicate within them. It cannot spread throughout the body and can only transmit genetic instructions. Instead of being held in little lipid balls, the weakened virus injects the genetic instructions into arm cells. Here, they make the parts appear like a part of the coronavirus spike protein – the knob-shaped structure that the virus requires to bind to cells. It primarily encourages the immune system to fend off later infection in the body, thus confronting the coronavirus. (McCrone, 2021)
4-Vaxzevria (AstraZeneca)	Developed from another virus (adenovirus), it has been altered to include the gene responsible for producing the spike protein of the SARS-CoV-2. It is needed by the virus to penetrate the cells of the body. Once administered, this vaccine introduces the virus gene into the body cells. They would then use this gene for generating the spike protein. When the immune system recognizes it as a foreign body, it will develop antibodies and trigger T cells to attack it. (EMA, 2021a, EMA, 2021b)
5- Sputnik	A combined vector vaccine, Gam-COVID-Vac, is based on rAd type 5 (rAd5) and rAd type 26 (rAd26). These vectors contain the full-length glycoprotein S gene (rAd5-S and rAd26-S) of the SARS-CoV-2. It had been known that antigens transmitted by adenoviral vectors trigger cellular as well as humoral immunity following a single immunization. It can be employed as an emergency prophylaxis method during a pandemic. Moreover, the combination of two immunizations results in a immune response of longer timespan. (Logunov et al., 2021)
6- Sinopharm	It is an inactivated virus vaccine; the genetic material of the virus has been removed to prevent the onset of disease. As inactivated viruses cannot replicate within the body, higher doses of the vaccine are required. Adjuvants (molecules that activate the immune system) are often used to improve the immune response. Usually, inactivated virus vaccines only cause antibody-mediated immunity (not cell-mediated immunity). (WHO, 2021)