Their immune systems are already messed up because
Post# of 72439
Also, we don't know if chloroquine actually works against COVID-19, or if it has a prophylactic effect. Your point would support the idea that it DOESN'T work -- except that when someone's immune system is messed up, we can't assume that what doesn't work for them wouldn't work for someone who didn't have the disease -- if you know what I mean.
That's why we need clinical trials, which fortunately are happening now.
As far as supply, two of the other big pharmas said that they would convert some of their manufacturing to make chloroquine. Of course, this means that there could be shortages of the medications they have to stop making to free up the production lines for chloroquine. So someone is going to NOT get a medicine they need. Hopefully it won't be something as crucial as HQ is to so many people.