Almost every lupus patient in the USA takes Chloroquine daily.
Why not do a quick study where all of these lupus patients take a COVID-19 test? See what the incidence of infection is.
That would answer the question with a huge study patient count.
That would be very interesting, wouldn't it? I can see some challenges.
It has been suggested that perhaps 85% of people get the virus and have no symptoms. Nationally, I think we are at 300k COVID-19 patients. Assume then that we actually have 1.8M patients.
Assume lupus affects 50 per 100k people in the U.S. and that all of them take chloroquine. That would be 150k people with lupus in the country.
These numbers might mean that one person in 1000 in the U.S. has COVID-19. That might mean that there would be 150 lupus patients with COVID-19.
Now comes the hard part. How do we sample the lupus patients in order to draw conclusions about how protected they are? If lupus patients are 50% protected, then there would actually be around 75 lupus patients with COVID-19. How many would we have to sample and what results would we have to get in order to conclude one way or the other?
One detail is that not every state has the same number of COVID-19 patients. If we don't take that into account and simply choose lupus patients at random throughout the U.S., then we risk getting a result showing good effect simply because we oversampled states with no or little COVID-19.
I'm sure that an actual study would have even more complications.