At this time, the data from 9 observational reports and one controlled trial suggest that hydroxychloroquine is dramatically more effective at preventing death from CoVID-19 than mechanical ventilation. It is encouraging to note that ventilated patients treated with hydroxychloroquine have been able to undergo successful extubation and transfer out of the intensive care unit onto the floor. Moreover, CoVID-19 viral loads have been reduced to low or undetectable levels after 5-15 days of treatment with hydroxychloroquine.

This is from the attached table showing the data for all of the studies. Seems like a pretty strong set of evidence.