Taking the antimalarial drug hydroxychloroquine did not prevent people from coming down with COVID-19 after being exposed to the disease.
Hydroxychloroquine doesn't prevent people from catching COVID-19, study finds : Read more
I've never seen, heard or read anything that suggested it did prevent people from getting infected! So far, there is NOTHING that has shown that it can prevent people from becoming infected . . . other than 100% total isolation. N95 masks don't 100% prevent infection, social distancing doesn't 100% protect against infection. No vaccines have been shown to 100% prevent infection (of course, they're still being developed).
In the USA (at least), this is largely a political thing in the media. If President Trump says anything, our media will run headlines that it is wrong, dumb, a lie, etc. . . I remember when he said based on what he'd seen and learned so far, his gut is that the death rate will likely be much more like 0.5% to 1.5%. The media lambasted him and quoted all sorts of scientists (including from the WHO) who suggested the death rate from Covid-10 would be in the 3.5% to 6+% range. And the media carried on with these claims for over a month. Of course, now that it is well established and recognized that even the 1.5% death rate (which was the highest end of Trump's estimate) is way too high versus reality! In all likelihood, the actual death rate will likely end up being very close to the 0.5% level, or even more likely, lower than that.
The scientists have gotten so much wrong with regards to Covid-19, actually, looking back at the February and March scientific statements and projections - scientists have gotten far more wrong than they have gotten right. But this is the general nature and history of science. I think we all seem to forget that science is wrong about 90% of the time . . . it is historical practice that the scientific community only finally gets it right (sometimes) after a lot of getting it wrong, learning from their many mistakes, bad theories and hypothesis and errors. This is not suggesting science should be ignored, but the reality is that science should often be taken as a grain of salt - in particular when it comes to NEW issues - which we know they have a tendency to get grossly wrong at the early stages of study and hypothesis. We also know and see, that much like society as a whole, the scientific community is very easily influenced by political beliefs and/or pressure - for better and for worse!