The human genome is full of endogenized DNA copies from retroviruses. Not only retroviruses but almost all RNA viruses can leave DNA footprints in mammalian
genomes. The viral DNA sequences from RNA viruses often cover single structural viral genes not the full-length viral genomes and are unable to produce
infectious virus particles. Molecular clocks allow to date endogenization events back to about 90 Million years, but they are still ongoing. Endogenous sequences
often maintain an open reading frame suggesting that they are selected for some function and supply some evolutionary benefits for the host. Indeed, the
sequences protect against superinfection by related viruses and against disease. The viral DNA copies require a reverse transcriptase for DNA synthesis from
the viral RNA. This enzyme is available from mobile genetic elements such as retrotransposons or LINEs which were shown to reverse transcribe the RNA from
Borna-, Ebola-, Marburg Disease and other viruses. Recently, Corona viral RNA has been described as DNA copy in the human genome. Again, only some viral
sequences were detected and no full-length genomes or infectious virus. RNA vaccines could potentially also contribute to some DNA copies even though this has
not been shown. The presence of such endogenized viral genes and their expression is of benefit for the host and protective against superinfection or disease.
This would include DNA copies from Corona viral RNA vaccines. A potential genotoxic effect due to integration and possible gene disruption cannot be excluded
but is estimated to be rare. The risk of gene toxicity is certainly lower for an RNA vaccine than for a Corona viral infection. Therefor a vaccination is beneficial and
we could even profit from protein expression of endogenized viral DNA as a genetic vaccine.
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