That's not a very precise answer.
As A biochemist who retired and was making vaccines and what we called experimental gene therapies ( mRNA vaccines) I can tell you these mRNA vaccines first of all do not work well. their mode of action is very different from normal vaccines;
why these mRNA vaccines are dangerous? I will just enumerate the a few points for the
covid 19 ""vaccine "" that is in reality an experimental gene therapy;
1- the mRNA encoding the spike protein, This protein if now known to be toxic for cells, the main point if that it encodes for prions among other things
2- the delivery method is as follows, the mRNA and all the contaminants from the vaccines production from cancereous cells are encapsulated in a special envelope ( LNP) these lipid nano particles were made to be charged slightly positively and bind weakly with any cells they touch, after being injected, the particles get to the blood where they reach ALL organs of the body, and penetrate cells mainly by the capillary of bodily organs, this was proven by pzfizer itself in bio distribution studies done in japan
before the release of the vaccine. Later this was confirmed by immunohistochemistry as they found the spike protein in many organs ( heart, pancreas, lung, liver, brain, heart ect...)
3- when normal cells are infected with a protein ( virus spike protein made by the mRNA, that does not belong there, the immune system does see it eventially as the spike protein being made in all the cells of the boby start to accumnlate because of overproduction they then start to be excreted by the affected cells and are present in the surface of the cells and are seen as a danger to the immune system, this lead to auto immune diseases...
I can continue for several pages but i will finish here with an example, all the news about sudden death in young athletes ( very rarely happenned before the vaccine and were mostly due to heart defects) are because the heart made this spike protein and was seen by the immune system of youg adults predominantly because the young have a stronger immune system than older adults. biopsy samples of these hearts were proven to contain spike protein ( it does not belong there at all and shoukd not be there at all ) it means the immune sustem attacked the meart cells infectsd and killed these cells leafinf to fibrous tissue in the heart reducing severely it's efficiency unto death under high stress as the heart does not function properly.