PROS1 and COVID-19: RNA-based vaccines. Different RNA variants have been tested over the years for the development of effective RNA vaccine that would still retain several core elements present in the intracellular mRNA, such as the cap structure (7-methyl guanosine), 5′-UTR, sequence coding for the target protein (SARS‐CoV‐2 S protein in the case of COVID‐19), 3′-UTR, and polyadenylation site.