If I recall correctly from when I was first put on hydroxychloroquine 5 years ago, there is research done by the veterans administration on veterans who served in the South Pacific theater in world War II who had autoimmune diseases and were also on hydroxychloroquine because there had been malaria where they were serving.
If I recall correctly, the veterans who had been on hydroxychloroquine for malaria treatment and prevention did long-term radically better with their various autoimmune diseases than those that did not.
I don't even know if the mechanism is fully understood, but it is a fact.
It is a useful medicine for those of us with autoimmune diseases.