Fantastic

So how early into infection would this have to be administered to be effective?

Any possibility of good news is its own ray of hope, but this is the fourth or fifth one of these we have heard. Most will not make it to market, hopefully a few will in time. Just the nature of clinical research trials, the success rate for FDA approval generally is around 14 percent. Even if they grant emergency waivers on some of these, we can probably expect similar success rates.
Worth a shot for sure though, especially for those on ventilators. Their survival rate is something like 34 percent. Not much to lose and a lot to gain for science.