COVID-19 vaccine: where are we now and where should we go?

Abstract

Introduction: The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has currently caused the pandemic with a high progressive speed and has been considered as the global public health crisis in 2020. This new member of the coronavirus family has created a potentially fatal disease, called coronavirus disease-2019 (COVID-19). Despite the continuous efforts of researchers to find effective vaccines and drugs for COVID-19, there is still no success in this matter.

Areas covered: Here, the literature regarding the COVID-19 vaccine candidates currently in the clinical trials, as well as main candidates in pre-clinical stages for development and research, were reviewed. These candidates have been developed under five different major platforms, including live-attenuated vaccine, mRNA-based vaccine, DNA vaccines, inactivated virus, and viral-vector-based vaccine.

Expert opinion: There are several limitations in the field of the rapid vaccine development against SARS-CoV-2, and other members of the coronavirus family such as SARS-CoV and MERS-CoV. The key challenges of designing an effective vaccine within a short time include finding the virulence ability of an emerging virus and potential antigen, choosing suitable experimental models and efficient route of administration, the immune-response study, designing the clinical trials, and determining the safety, as well as efficacy.

Keywords: SARS-CoV-2; clinical trials; covid-19; vaccine.

Figure 1.

The host immune responses during SARS-CoV-2 infection and vaccination. SARS-CoV-2 uptake through the aerosolized then infects the cells that express the surface receptors angiotensin-converting enzyme 2 (ACE2) such as alveolar type 2 cells. The virus may suppress the antiviral interferon (IFN) type I responses which result in uncontrolled replication of viral. Recruits the neutrophils and monocytes, as well as macrophages, caused the cytokine storms which means the overexpression of pro-inflammatory cytokines and chemokines. Moreover, non- neutralizing antibodies produced via B cells may enhance the SARS- CoV-2 infection via antibody-dependent enhancement (ADE) which results in increasing organ damage. While in the healthy immune response which receive vaccine, the initial inflammation recruits the CD8 + T cell as well as CD4 + T cell to the infection site then results in killing the infected cells before the virus spreads. Moreover, neutralizing antibodies in these individuals can block viral infection

Figure 2.

(A) Schematic of the overall structure of SARS-CoV-2; (B) Comprehensive selection of SARS-CoV-2 recombinant proteins full-length spike, spike subunit 1, spike subunit 2, and receptor-binding domain produced from various expression system

Figure 3.

The clinical development vaccines for COVID-19