I watched a brief news clip this morning with a very articulate and informative Doctor, talking specifically about Boris Johnson's situation.
Albeit he said he was having to base it on his own informed assumptions and experiences, what is likely to have happened is that when they conducted tests on Boris's bloods when he reported continuing symptoms, they were at a dangerously low level of oxygenation so they have been administering oxygen, not by ventilator because he was able to breathe for himself, but via a normal oxygen regulator, to get the 02 levels back up.
The other interesting point the Dr made was that, even though a person with CV may look "OK", it does not necessarily mean that their oxygen levels aren't on the decline, as the virus takes a grip over days. It is often imperceptible, but the mechanics of the respiratory system are compromised by the virus so it stands to reason they aren't able to pull in a healthy level of O2. By the time the person feels really poorly, things have already deteriorated over those days, and it gets to breaking point.
This is what happened with Boris, and him continuing to work 16 hours a day, not listening to his body contributed to his health declining.
Having seen a YouTube advice yesterday about the benefits of deep breathing, it's worth us all getting ourselves prepared even before we (potentially) contract this virus.
Daily deep breathing sessions, twice a day, can be all it takes to stop things deteriorating, because you've already primed the pump, every little helps. It's like dehydration, drink steadily over time to prevent dehydration, rather than getting really thirsty because by then it's too late, the body is already dehydrated.