https://www.sciencedirect.com/science/article/pii/S096007602...
“Effect of calcifediol treatment and best available therapy versus best available therapy on intensive care unit admission and mortality among patients hospitalized for COVID-19: A pilot randomized clinical study”
This one was actually about giving some patients calcifediol/vitamin D doses as part of the treatment, and comparing what happened to those who received the vitamin injection and those who didn't.
tldr: "of 50 patients treated with calcifediol, one required admission to the ICU (2%), while of 26 untreated patients, 13 required admission (50 %).")
Performed at Reina Sofia University Hospital, Córdoba, Spain.