He's not on a ventilator yet. In fact, it appears to be something of a mystery as to exactly why he is still in intensive care if, as is claimed, 'He is receiving standard oxygen treatment and is breathing without any other assistance.' It would appear that either they are lying or he is receiving preferential treatment. Both are entirely plausible.
ETA: Just to add to that, regarding his survival odds, looking at the Swiss stats, around a quarter of people who have gone to hospital in Switzerland have ended up in ICU, and nearly all of those have ended up on ventilators. Once you're properly in ICU, ie unable to breathe for yourself, that's when the grim 50:50 odds kick in. If they are telling the truth about his current condition, his odds are a fair bit better than that at this moment.