I don't have a huge problem trying to initially test the ability of chloroquine to reduce viral infection with the exclusion of co-morbidities and severe symptoms.
First, writing up a drug or vaccine clinical trial is a huge pain in the ass because of how things are reported, there's a reason why every drug has an extensive side-effects list. Any and all conditions that occur when running a trial need to be listed, stub your toe throw it on the list.
Second, it seems like through trump and the media that the drug is toted as a miracle cure when in reality it should be used as a front line defense/prophylaxis. Its initial use was throwing it at people who were deteriorating fast and used as a compassionate use we need to try anything or this person dies, since it wasnt a controled study in China some people lived and the its a miracle cure spread.
Third, the reason why it should be used as a front line defense/prophylaxis is that you are trying to treat a virus. Treating a virus is a hell of a lot easier when the viral load is low than when it is high. The mechanism of action for chloroquine in helping with Covid-19 is believe to be two fold, its modifies the pH of cells so that after the entry of viral RNA its not an environment conducive to viral replication and its also an immune modifier which helps with the cytokine storm that progresses in some severe patients.
If you want a comparison of an anti-viral then a good one would be Oseltamivir, which people would know as Tamiflu. Tamiflu works by inhibiting neuramidase the flu protein response for viral escape from infected cells. Simplistically speaking if you take tamiflu cells that are infected can no longer make more virus because the virus replicates wont be able to leave the already infected cell. Problem is it really only works when viral load is low, best to take tamiflu before symptoms even occur or within 24 hours of symptoms after that it will "reduce the duration" but a study would be instead of feeling like shit for 7 days its now 5.5/6 days. If you took it before you were ever exposed to the flu, you would essentially be protected because the initial infection would not be able to replicate efficiently.
That example holds up for most viruses, if you have a viral load of 1,000 pfu then you can control it if you wait till its been days and you now have a viral load of 1,000,000,000 pfu then it doesnt matter what you throw at it the virus is going to still exist unless you have a drug that's widely penetrating with a highly specific mechanism of action. What you have with chloroquine is a very non-specific treatment that might tilt the scales to a positive outcome in a 60/40 split for extreme cases but may make a 70/30 difference if given early, but even that has its caveats that need to be tested.
