There was significant interest in zinc early on. It seemed like one of the most promising avenues for protecting oneself against Covid-19. Searching on both Google and Lesswrong itself, I do not see new research on it. (This is the closest thing I found; A metareview that says there is almost no research whatsoever.) Its epistemic status seems frozen in the pre-Covid past: promising experimental treatment with no significant evidence confirming or disconfirming it, and no largescale commercialization and deployment.
This seems quite an inefficient result, if my understanding is correct. What has gone wrong?