Based on these risk considerations, the original idea behind using mRNA as a drug (for genetic therapeutic or vaccine purposes) was that mRNA is typically degraded quite rapidly once manufactured or released into a cell. mRNA stability is regulated by a number of genetic elements including the length of the “poly A tail”, but typically ranges from ½ to a couple of hours. Therefore, if natural or synthetic mRNA which is degraded by the usual enzymes is introduced into your body, it should only last for a very short time. And this has been the answer which Pfizer, BioNTech and Moderna have provided to physicians when asked “how long does the injected mRNA last after injection”.
But now we know that the “mRNA” from the Pfizer/BioNTech and Moderna vaccines which incorporates the synthetic nucleotide pseudouridine can persist in lymph nodes for at least 60 days after injection. This is not natural, and this is not really mRNA. These molecules have genetic elements similar to those of natural mRNA, but they are clearly far more resistant to the enzymes which normally degrade natural mRNA, seem to be capable of producing high levels of protein for extended periods, and seem to evade normal immunologic mechanisms for eliminating cells which produce foreign proteins which are not normally observed in the body.
