Dosing of pharmaceuticals in a pill or injection is a very technically complicated thing. When you swallowed a pill in the 1970s, a significant portion of the active pharmaceutical ingredient (API) was destroyed by stomach acid before it ever made it into the body to do what it is intended to do. If your API is wildly expensive this is especially bad. There is an entire industry of excipients that are used to deliver the API in a protective way in current pharma industry. They design it so it delivers most of its cargo in the intestines.

Maybe the delivery system with mRNA is the issue. You are wrapping it in a PEG-LNP sphere otherwise the RNA is instantly destroyed. Cells take up the spheres. Some of those mRNA bundles will burst and degrade before they ever get to the cell. Maybe their calculations were off on how much wouldn't make it into the cell so they grossly overloaded it, but the mRNA bundles survived at higher rates. Or maybe the risk was in overloaded lots in conjunction with shots that make it into the blood stream.

It is also possible all 3 companies had other contamination issues in their production systems.

But I think Gen is right, this at first blush sounds more like a dosing issue to me. And Pods is quite correct too.

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I'm not letting my ship get shot out from under my ass! Open fire! - Captain Lindemann