Coronavirus disease 19 (COVID-19), a severe respiratory disease caused by infection with the novel SARS-CoV-2 virus, has impacted almost every nation globally, making it a pandemic. More than 4.91 billion doses of vaccines have been administered worldwide, but the number of infections continues to rise. mRNA-based vaccines have been developed to bring the pandemic under control in some parts of the world. This brief review will give an overview of how mRNA vaccines work and what we can learn from the transcriptome of COVID-19 patients to identify the significant marker genes responsible for disease severity and mortality.