In previous posts I described how the two currently approved mRNA vaccines both use ‘modified nucleosides’ to enhance their efficiency. Meanwhile, a company called CureVac has created an mRNA vaccine that uses regular, unmodified, RNA. It is currently being tested in large scale trials. In this post I explain what the challenges are with this plain RNA approach, and we reverse engineer quite closely what CureVac has done with regular RNA to (hopefully) deliver an effective vaccine.