My daughter (high risk) got Covid. Was treated immediately with Regeneron and then Ivermectin a few days later.
She said Ivermectin was much more effective than the Regeneron.
By the way, Ivermectin has been used for years for other treatments by physicians. Horses take antibiotics too.
But, I'd imagine the Japanese start at a far better baseline. Little obesity, diabetes, much better diet, probably less overall systemic inflammation.