In regards to Risch paper, there is a March 2021 Lancet paper (see at the end) that refers to Risch and concludes that were no benefits. There was also a letter showing that described non-randomized experiments were not statistically valid. To trace this further, you can go to medline or pubmed or google scholar or any other citation system, find the paper you care about, and then look up later papers that cite your paper. Some may just include it into a list, but some might actually be a follow-up.
from a quick review pf Risch paper, I noticed 2 things:
1) a way to correct non-randomized trials is to match patients by their demographics – age, gender, health status. I don’t see this done
2) paper quotes one result that HCQ-AZ achieves 25x benefit, while HCQ by itself achieves 4x benefit. Given that later argument shifted to HCQ-AZ helps while HCQ does not, the quoted 4x benefit is a red flag – if this is a false conclusion
Christine Johnston et al, Hydroxychloroquine with or without azithromycin for treatment of early SARS-CoV-2 infection among high-risk outpatient adults: A randomized clinical trial