• DNA vaccine consists of delivering genes or fragments of it, encoding immunogenic antigens to the host's cells by using DNA plasmids as a vector.

• Compared with traditional live or attenuated vaccines, DNA vaccines have several advantages, such as induction of broad immune responses without any risk being associated with replicating microorganisms; stimulation of both cellular and humoral immunity; construction of a vector encoding different antigens in a single vaccine; efficient large-scale, low-cost, production; and high storage stability

• A clinical trial was designed to evaluate the safety and tolerability of orally immunized bacTRL-Spike vaccine in healthy adults. However, this study has not yet started recruiting, and the estimated completion date is December 31, 2021 Moreover, the safety and immunogenicity of GX-19, another DNA vaccine against COVID-19 that uses intramuscular immunizations are already in clinical trials.

• mRNA vaccines do not need to reach the cell nucleus like the DNA ones, which is one of the potential practical advantages. The mRNA-1273 (Moderna Inc. Cambridge, MA, USA) was the first mRNA vaccine to be designed against COVID-19 and has achieved a time record of 63 days from vaccine design to human trials.

• Developing vaccines against COVID-19 require further studies on gene mutations and how to avoid vaccine failure because of them.