HCQ, quinines, worked well in the lab against SARS on test tissue. 2005 study. When it was tried on people as a prophylactic for covid, SARS-2, it was a disappointment. The subjects caught covid at the same rate.
I don’t think it is useful as a prophylactic, though Ivermectin has shown some promise there.
I didn’t think HCQ and IVM were being pushed as a prophylactic, thought I could be wrong.
They do see in countries where people are taking them in an ongoing state for other things, that the incidence is lower which would indicate a prophylactic component, but that is all I know about it in that respect.