CDC has a webpage pointing to the FDA / NIH web-pages.
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As far as I can tell, "IVM doesn't work vs COVID19" is the official stance of US health research institutes. There are further studies because the politics of it kinda demand a study, but no one expects the studies to have a good result. (Nothing like monoclonal antibodies, which are being used to save lives right now).
This isn't a "we don't know" stance. FDA is very explicit to not use IVM for COVID19.
https://www.fda.gov/consumers/consumer-updates/why-you-shoul...
> Currently available data do not show ivermectin is effective against COVID-19. Clinical trials assessing ivermectin tablets for the prevention or treatment of COVID-19 in people are ongoing.
From https://emergency.cdc.gov/han/2021/han00449.asp
> Ivermectin is not authorized or approved by FDA for prevention or treatment of COVID-19. The National Institutes of Health’s (NIH) COVID-19 Treatment Guidelines Panel has also determined that there are currently insufficient data to recommend ivermectin for treatment of COVID-19. ClinicalTrials.govexternal icon has listings of ongoing clinical trials that might provide more information about these hypothesized uses in the future.
Those are "we don't know" stances. Or at least, "we're not certain".
The CDC's stance is "we don't know, there's trials ongoing", not "it doesn't work".