https://www.scientificamerican.com/article/nih-official-fauci-hiv-vaccine/
His reasoning for terminating a clinical trial:
No efficacy at all, because it wasn't done in a large enough trial or among at-risk people, who would allow enough infection to occur to see if it would work. All it showed was safety to some degree—I mean, we didn't do a lot patients—but safety in those we looked at. And the fact that it induces an immune response, which one would argue was somewhat better than what you saw in the STEP trial.
There was some argument about that at several meetings. "Somewhat better" is what? A lot better? I didn't think it was a lot better.
If there were no other promising avenues - why would he terminate clinical trials? The possibility of "a little better" has no value to him? It just seems bizarre.
A vaccine might be more likely with Covid-19 because of its design vs. HIV. HIV can be better controlled through behaviors and PREP. Covid-19 spreads quickly through the air.