I have a relative who is a microbiologist and researcher who has a patent pending for a vaccine, so he is very familiar with the testing procedures and requirements for FDA approval. He and his wife have been vaccinated against Covid, and they trust the science that went into that vaccine development. But this is what we know - the mRNA vaccines like the Covid vaccine have been studied for a long time before this pandemic for treatment of other issues like HIV, Zika and flu.And the makeup of the vaccine allows scientists to design the mRNA in a way so it does not stay in the cell longer than needed to generate immunity. While concern about long term effects is legitimate, people need to be aware of the misinformation out there. The anti-vaccine industry is very organized and is trying to move people to extreme positions about vaccines using conspiracy theories and false narratives. In some cases these groups simply do not believe in science, and in other cases, they hope to profit by selling other products to "protect" against Covid. In any event, respected scientists are saying that the Covid vaccines would not be expected to cause long term side effects.
http://https://www.chop.edu/centers-programs/vaccine-education-center/video/what-are-the-long-term-side-effects-of-covid-19-vaccine