# Glen Raphael comments on Covid-19: My Current Model

• That study made me much more inclined to think HCQ is useful as a prophylactic.

Among the full study group there was a reduction of illness of a bit over 17% but it’s better than that: the study’s supplementary appendix includes a chart that breaks out various subgroups including a breakout by DAY. The most benefit was found for people who started treatment on day ONE post-exposure. Next best was starting on day TWO post-exposure. By day three there was a negligible benefit and by day four there was a negligible harm—that subgroup actually did a bit worse than the control group.

So to get an average 17% improvement across the whole group we’re combining two start days of positive improvement (days 1 and 2) with two start days that (eyeballing the chart) round off to roughly zero improvement (days 3 and 4). Since the N was pretty evenly spread across days, basic math says if we JUST looked at the benefit for people who start as early as day 1 or 2 we should expect to find about twice as much improvement which is to say a ~34% reduction in illness!

Given the curve on that data, I’m optimistic about prophylactic use; it’s possible that starting on day 0 or day −1 does even *better* than 34%. And (contrary to the retracted studies) they found no evidence at all of serious side effects or heart issues.

If this study result replicates then people who obtain HCQ in advance (so they don’t have to wait for study enrollment or shipping) and start taking it *immediately* upon known exposure are ~1/​3rd less likely to show any symptoms of covid than if they didn’t do that. Which could save thousands of lives. (We can’t be 95% sure of this result yet because the study was too small, but less-than-perfect knowledge is still knowledge and under the current circumstances probably worth acting on.)

(Caveat: they didn’t find benefit for age>50, the group we care most about. Caveat to the caveat: there were only 5 people in the “control” for age 50 - they didn’t have nearly enough oldsters enrolled in the study to expect meaningful results for them.)

• Thank you for looking deeper into this. A likely 13 reduction when taking it on day 1 is amazing. And if people at risk take it routinely (“day zero”) it might be even better. I guess I have to update back to 40% likely it works.