This isn't right. Risk from overdoses of drugs, poison, and allergens is *highly* nonlinear. It'd be exceptionally unlikely in the case of mRNA vaccine, but that's the case the majority of the time.

There's a specific minimum dosage most people have of allergen before they hit on a life-threatening reaction. You might be okay with trace amount of peanuts, swell up with one peanut, and die with five. It's pretty consistent, and very nonlinear.

That's why you can build up a tolerance to iocane powder too; small doses won't do anything, while large ones are guaranteed to kill. If it was linear, a 1/10th lethal dose would have a 10% chance of killing you.