In reply to BnB:
> Once infections have peaked in the current lockdown, why not keep the most vulnerable in lockdown (tough on them I know) and allow immunity to build in the more robust, more economically productive, and much larger, segment of the population who can be encouraged back to normal life, thus rebooting the economy? I understand this may have to be phased in, to manage the strain on the NHS, but the instances of hospitalisation among less vulnerable groups are, by definition, far lower.
I think the problem is that this process will be very slow. And then you might as well wait for a vaccine.
Some numbers for the fun of it (don't take this too seriously, I am improvising here ):
current UK number of reported cases: order of 15.000. This seriously underestimates the amount of actual cases as only serious cases are reported. Let's assume there are actually 200.000 cases in the UK.
If the UK would be able to manage this level of cases, with 200.000 cases per month, the time needed for herd immunity is 40M/200k = 200 months.
Even if the UK would be amazing and manages 2M cases a month, it would still take about the same time as the expected time for a vaccine to become available.