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.
Using vaccines with or without the adjuvant as an enhancement for immunogenicity during the development of the COVID-19 vaccine is another challenge. Investigating vaccine safety toward different pathogens can be possible through animal model experiments as well as clinical trials, which are very challenging in the small-time duration of this pandemic. In addition, there is a concern in the field of the live attenuated and inactivated vaccine which may revert to virulence. Thus, safety is considered as one of the most important challenges in the rapid development of the vaccine. Designing a vaccine within a short time is another main challenge, which includes detection of potential antigen, administration route, animal model experiments, the immune-response study, clinical trials, determining the safety and efficacy, etc. Possible COVID-19 vaccine should be designed to be suitable for different age groups without interfering with other vaccination protocols in pediatrics. Other challenges are large scale production of vaccines with the high purity of the antigen, sufficient antigen, and half-life stability. Source: Full article: COVID-19 vaccine: where are we now and where should we go?