Dr. Gerald Zon’s latest “Zone in with Zon” blog post, dated May 25, 2021, and published by TriLink BioTechnologies of San Diego (www.trilinkbiotech.com), discusses the key component for the Pfizer-BioNTech and Moderna mRNA vaccines, namely the chemically modified mRNA (modRNA) synthesized by in vitro transcription (IVT) reactions, wherein one of the natural (aka wild-type) A, G, C, and U nucleotide 5’-triphosphates is replaced by a base-modified analog. Dr. Zon notes that interest in chemically modified mRNA (modRNA) (onlinelibrary.wiley.com/doi/10.1002/jmv.26924) can be traced back to a 2005 report by Karikó et al. (pubmed.ncbi.nlm.nih.gov/16111635/) demonstrating that modRNAs comprised of 5-methycytidine (5mC), N6-methyladenosine (m6A), pseudouridine (Ψ), 5-methyluridine (m5U), and 2-thiouridine (s2U), either separately or in combination, can reduce immunogenicity mediated by toll-like receptors (TLRs). Dr. Zon notes that “subsequently, it was shown that Ψ modification, in particular, could increase the translational capacity and biological stability of mRNA (Karikó et al. 2008) (pubmed.ncbi.nlm.nih.gov/18797453/). Along the lines of the familiar saying ‘good, better, best…,’ later studies by others (Andries et al. 2015) (pubmed.ncbi.nlm.nih.gov/26342664/) found that simply adding a methyl group to the N1 position in Ψ (N1-methylpseudouridine, N1mΨ) in modRNA via IVT with the corresponding 5’-triphosphate produced N1mΨ-mRNA that outperformed Ψ-mRNA.