Messenger RNA (mRNA) vaccines (like Pfizer and Moderna) do not alter your DNA.
In fact, they lack all of the basic requirements necessary to alter DNA. In other words, it’s biologically impossible.
In order for a mRNA vaccine to alter someone’s DNA, several events would have to occur…
mRNA would need to enter the cell nucleus, where DNA lives. However, mRNA do not have the “secret door code” (called nuclear access signal) that would allow it to enter. mRNA vaccines can’t get in.
If the mRNA vaccine did get in (which it won’t), mRNA would have to be then converted to DNA. This would require a tool called “reverse transcriptase”, which the vaccine doesn’t have.
Also, if it made it into the nucleus, mRNA would then to need to insert itself into the DNA. The mRNA would need a tool called “integrase” to do this, which the vaccine doesn’t have.
mRNA is found in all living cells. So, sorry to break it to you, but you already have mRNA within you. This is because our cells need instructions on how to function. The mRNA vaccines add a chapter to this instruction manual: “how to properly to fight the COVID19 virus”.
Some vaccines are being developed and tested to target DNA. And they are also safe (but I can explain at another time). Also viruses like HIV can integrate themselves into DNA, but this isn’t true of all viruses, and HIV can only do so with the help of special tools. None, of which, the COVID19 vaccines have.