Zinc has antiviral properties. It has been shown to stop Sars Cov2 replication in-vitro. Cells limit their Zinc intake. HCQ facilitates Zinc getting into cells.
So I'll see, for example, some otherwise-highly-credible UCSF researchers mention a bunch of evidence they think puts the potential of HCQ to help to rest, without any mention of Zinc considerations (even in passing, or to ridicule, or to share why they don't think the link credible). But even coincident upon the very 1st discussions of HCQ as having potential, Derek Lowe shared an anecdote about how carrying-Zinc seemed essential to Chloroquine-related-compoounds' bioactivity (https://blogs.sciencemag.org/pipeline/archives/2020/03/20/ch...).
And, in many parts of the world, HCQ – as a cheap drug that, in moderate doses with proper monitoring, is very low-risk – is already considered part of the Covid-19 "standard-of-care". So, it's given even to the 'control' arms of trials for other compounds – making both its effects, and those other compounds' effects, harder to disentangle.
All I want now is true randomized trials - and can't at least one of those monitor, or vary the supplementation of, Zinc as well?
In vitro results are much less meaningful than in vivo results. It can be a useful early validation step, but is far from telling us anything about real world efficacy.
There's enough in vivo studies at this point that in vitro studies should no longer be part of the conversation.