No, this does not imply that going from 80% to 90% vaccinated could halve the number of hospital beds needed - that reasoning would only work if the vaccine com

No, this does not imply that going from 80% to 90% vaccinated could halve the number of hospital beds needed - that reasoning would only work if the vaccine completely prevented Covid-related hospitalizations, in which case zero vaccinated people would be hospitalized and Simpson's paradox wouldn't apply. What it actually implies is that at much less than 100% vaccination, you hit a point where vaccinating the remaining population does very little to reduce pressure on hospitals because most people who're hospitalized have been vaccinated, despite the fact that the vaccines do reduce the risk of hospitalization. That is, the benefits of vaccinating the last few percent of the population actually diminish rather than increasing like they would do with a more effective vaccine.