It would be useful to have the original paper. It seems the question is weather it works to prevent people from ever getting Covid versus how well it works once they are actually infected.
Interesting:
“ Chloroquine has antiviral effects. It increases late endosomal or lysosomal pH, resulting in impaired release of the virus from the endosome or lysosome – release requires a low pH. The virus is therefore unable to release its genetic material into the cell and replicate.
Chloroquine also seems to act as a zinc ionophore, that allows extracellular zinc to enter the cell and inhibit viral RNA-dependent RNA polymerase.”
Biochemical and Biophysical Research Communications—
Volume 323, Issue 1, 8 October 2004, Pages 264-268
”In vitro inhibition of severe acute respiratory syndrome coronavirus by chloroquine”
https://www.sciencedirect.com/science/article/pii/S0006291X0401839X?via%3Dihub