I don’t think there’s any proof of this. Do you have a source for the hospitalisation rates still being too high for the NHS to handle?
Well, just as a rough marker, I think under 40s have something like a 2% chance of hospitalisation. Which doesn’t sound much, but scales up quickly if infections are widespread.
Plus the issues around variants, if the virus is still circulating widely. That’s arguably the much bigger issue.
They estimated that they’d need 80% vaxxed to achieve herd immunity and that has to take into consideration those who can’t be.