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The mRNA-based vaccines cannot lead to COVID-19 or its symptoms since they only lead to the production of the spike protein in the cell.

However, the spike protein itself can lead to cell fusion: Quantitative assays reveal cell fusion at minimal levels of SARS-CoV-2 spike protein and fusion from without

Is this a potential risk of the mRNA vaccine ? I could imagine, that the spike protein needs to be bound to the virus to induce this effect ? I could not find any literature where the effect of the unbound spike protein is tested.

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  • $\begingroup$ Why the down vote ? $\endgroup$ – Felix Z. Feb 23 at 23:11
  • $\begingroup$ The virus membrane anchored spike provokes virion-cell fusion, the cell membrane anchored spike provokes cell-cell fusion, when encountering ACE2. In most vaccines the 2P mutation greatly reduces this behavior (not in the AstraZeneca vaccine). $\endgroup$ – reuns Feb 27 at 14:04
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The mRNA vaccines encode a mutant version of the spike protein in which the structural transition needed to to fuse membranes is blocked. This was done to make the immune response focus on the pre-fusion state, which is much better for neutralizing the virus.

From https://cen.acs.org/pharmaceuticals/vaccines/tiny-tweak-behind-COVID-19/98/i38:

Fortuitously, Graham and a former postdoc, Jason McLellan, devised a solution to this problem before the pandemic. Through a bit of structural biology and persistent protein engineering, McLellan discovered that adding two prolines—the most rigid of the 20 amino acids—to a key joint of a vaccine’s spike protein could stabilize the structure’s prefusion shape. This 2P mutation worked in preclinical studies of Graham and Moderna’s MERS vaccine, so they applied it to Moderna’s COVID-19 vaccine.

I don't know if cells expressing wild-type spike protein would fuse into syncytia, but it seems very unlikely to happen with the vaccine spike.

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  • $\begingroup$ Any peer reviewed source of the study they did to demonstrate this.? Cause it’s an extremely complex and involved process to engineer that kind of outcome. $\endgroup$ – froimovi Feb 25 at 8:48
  • $\begingroup$ here's one: science.sciencemag.org/content/369/6510/1501 it and many others are linked in the C&E News article I linked in the answer. The article is, imo, quite good. It gives an overview of the years of work and trial and error that led to this solution being available when the pandemic arrived. $\endgroup$ – timeskull Feb 25 at 15:16
  • $\begingroup$ does that paper show that this artificial variant of the spike protein, when it is synthesized inside a human cell, Can’t fuse with the cell membrane? The point is to present the spike protein on the outside surface of the cell —to be exposed to antibodies. So this paper showed that the perfusion spike protein can make it, again, from the inside of the cell, to a position where it’s exposed (on the cell surface) to the extra cellular environment (all the while remaining in the pre-fusion state?). $\endgroup$ – froimovi Feb 25 at 15:45
  • $\begingroup$ I see what you mean now. No, I don't think anyone has directly tested if spike proteins that were expressed by a cell due to mRNA vaccines are or are not capable of fusion. It follows that they aren't from logically connecting other results, e.g. membrane fusion depends on transition from pre- to post- state, that transition is blocked by proline substitution, antibodies produced by the vaccine only bind to the pre-fusion state, etc. You might want to ask this as a separate question if you want more info. $\endgroup$ – timeskull Feb 25 at 15:57
  • $\begingroup$ Dude, This vaccine is not legitimate. And wasn’t legitimately developed. At all. Not this one. I’ve done my research and due diligence. Don’t care to look further into more stupid wasteful studies, from journals that have lost an unbelievable degree of credibility in the last year. Probably safe to take the vaccine, but yeah, as far as it working through this mRNA mechanism — no one knows that it’s doing that (or doing anything actually). $\endgroup$ – froimovi Feb 26 at 6:15

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