[JaneC (OP)]

It may take 18 months to develop a vaccine--or indeed, it may prove impossible to do so (as has been the case with some other viruses.)  In light of that, what hope is there for an "extremely vulnerable" person ever to be able safely to leave isolation?

[Petrochemicals]

Herd immunity, of enough of the healthy have the virus it will dissipate and vanish giving enough time for a vaccine to be developed.  The medical  problem with the social restrictions is its not givong enough heard restrictions, the flattening of the curve is extending the time the virus is present. Given its a new virus everyone bar the percent that are naturally immune are susseptable to it, so its spread is very pernicious. The extension of coronas dwell time is not good, if 1 month becomes 6  chances of infecting the vunerable increace by more than 6.