https://ijvtpr.com/index.php/IJVTPR/article/view/23/51
For example, this recent Swedish paper detailing in-vitro DNA modification (reverse transcription) by COVID-19 vaccine mRNA, in human liver cells:
https://www.mdpi.com/1467-3045/44/3/73/htm
And this is just one of many concerns (and the above paper isn't the only verification of that particular concern). For example the proprietary lipids fascilitating the entry of the mRNA into cells have been shown to exhibit high cytotoxicity.
Coupled with ongoing legal revelations as a result of FOIA requests - https://phmpt.org - regarding what the FDA knew about the safety profile of the shots, versus what they told the public at the time, along with FDA's otherwise bizarre reticence to release such data that is clearly in the publics interest, these shots are seeming less and less "safe and effective" by the day. (Lawyer Aaron Siri does some write ups regarding this FDA case.)
Indeed, it's common knowledge now the "effective" part was mishandled, so it shouldn't be surprising - especially, in a social and media climate actively preventing emergent negative signals - that it might turn out safety was mishandled also.