I think in order to quantify risk-vs-number-of-vaccinations, we need to understand the type of risk itself and how the vaccine might have unintended effects. If we assume all of the unintended effects are longer-than-expected presence of the mRNA (or otherwise vector) and its derivatives, then the risk of noticeable adverse consequences doesn't really sum up because any accumulation effects will be negligible. I.e. the amount of substance is low - 1 ng/kg body mass is same as 2 ng/kg body mass. Relatively it's a lot but it's not a lot if consider the body a "resilient/tolerant" system.
May I ask for more detail on what this means? All I got from this is that since employees couldn't work from home (on weekends, say, as one might do in a software role), the net effect of 20% was that 3M got 20% overtime from employees for free. And that the returns on the 20% time were very significant because process improvement/intensification (a primary enjoyable skill of of 3M engg talent) has very high RoI in general.