A couple of years ago, mRNA vaccines remained at the research stage. Now, they are among the best-selling pharmaceutical products with Pfizer (NYSE:PFE), BioNTech (NSDQ:BNTX) and Moderna (NSDQ:MRNA) dominating the market. However, that could change in the long run as a growing number of companies develop next-generation mRNA COVID-19 vaccines, which promise to be more effective…