Among genetically engineered drugs, those with mRNA active ingredients are a special case, as their cell-free biosynthesis requires high concentrations of DNA templates, which must be removed before the products can be used as drugs. In the case of the COVID-19 mRNA vaccine Comirnaty® produced by BioNTech/Pfizer (BNT162b2) (Mainz, Germany), these templates are produced by plasmids obtained from bacterial cultures [1]. Thus, Comirnaty® has a special quality: DNA impurities are possible due to the manufacturing process; this may be relevant for all genetically engineered drugs, but it is otherwise rarely a problem [2]. This is due to the fact that genetically engineered active substances are predominantly proteins, which can be easily separated from DNA due to their chemical differences. Accordingly, DNA impurities in genetically engineered medicinal products have so far only been a marginal issue. However, the situation is quite different with mRNA vaccines: contaminating DNA and active ingredient mRNA are both nucleic acids and therefore chemically so similar that separation is far more difficult than separating DNA during the purification of protein active ingredients [3].
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