In a thorough article by Archa Fox, Jen Martin and Traude Beilharz, the trio broke down the myths about the Pfizer and Moderna COVID-19 vaccines altering people’s DNA and explained why this would be extremely rare. And those rare cases?
There are some extremely rare exceptions. One is where genetic elements, known as retro-transposons, hijack cellular mRNA, convert it into DNA and insert that DNA back into your genetic material.
Some retroviruses, such as HIV, also insert their RNA into our DNA, using similar methods to retro-transposons.
However, there is a vanishingly small chance of a naturally occurring retro-transposon becoming active in a cell that has just received a mRNA vaccine. There’s also a vanishingly small chance of being infected with HIV at precisely the same time as receiving the mRNA vaccine.
So, yeah, it’s not impossible but it’s so significantly less likely to have it happen to you compare to, say, contracting the virus and becoming seriously ill and/or dying? I’m no gambler but I’d go all-in on “get the vaccine”.
See also: Why COVID-19 vaccines aren’t comparable