If you are interested in how complicated the supply chain of the Pfizer/BioNTech and Moderna mRNA vaccines are, this article by Jonas Neubert is what you might want to read. It is gives a quite in-depth overview of the manufacturing process and its bottlenecks.
One of the major problems seems to be the coating of mRNA in liquid nanoparticles (LNP). Producing these LNPs is one part, but apparently actually mixing them together with the mRNA is even harder.
One thing … more