Impossible to answer. We simply don't have data to show whether this would be effective as prophylaxis even if we knew it worked against COVID-19.
I'm already on 400mg Plaquenil for inflammatory poly arthritis. Assuming it's helpful for COVID19, is this offering me extra protection? Note: I am not looking for way around any guidelines, we are being very strict with social distancing, disinfecting high touch surfaces daily, and following our stay at home orders. I'm more curious, really! And wondering if it's safer for me to be the one who goes to the grocery store when needed. Thanks!