If the severe critical trial showed overwhelming e

If the severe critical trial showed overwhelming evidence of less deaths already why wasn’t the trial stopped for efficacy . Not enough patients 51 to do that even if placebo had let’s say 4 deaths and none with Lero ?? I don’t get it . Someone explain please and thank you .I know it original said 390 but didn’t N P say screw it we are stopping at 51 and looking at data then ??? Am I confused here or not ???