Yes there are few that claim 100% efficacy and no side effect at this stage, but there are
far, far, far fewer who make it to human availability.
I wouldn't describe it working in humans as "a stretch" per se. I'm not identifying a specific reason it shouldn't work in humans. I'm just saying that's true of thousands and thousands of really great looking treatments (per year!) that, nonetheless, end up not working in humans, or not being convincing enough to even warrant putting them in humans once.