We have been told that SARS-CoV-2 mRNA vaccines cannot be integrated into the human genome, because messenger RNA cannot be turned back into DNA. This is false. There are elements in human cells called LINE-1 retrotransposons, which can indeed integrate mRNA into a human genome by endogenous reverse transcription. Because the mRNA used in the vaccines is stabilized, it hangs around in cells longer, increasing the chances for this to happen. If the gene for SARS-CoV-2 Spike is integrated into a portion of the genome that is not silent and actually expresses a protein, it is possible that people who take this vaccine may continuously express SARS-CoV-2 Spike from their somatic cells for the rest of their lives.