Pre-Exposure Prophylaxis study (treated before exposed to the virus)
et al., medRxiv, doi:10.1101/2020.05.04.20089904 (Preprint)
Association of previous medications with the risk of COVID-19: a nationwide claims-based study from South Korea
Database analysis of many drugs and COVID-19 cases, with 23 cases taking HC Q, and 251 control patients not taking HC Q, showing OR 1.07, p=0.77, and in multivariable analysis OR 1.48, p=0.086. Patients taking HC Q are most likely taking it for systemic autoimmune diseases where the risk of COVID-19 is much higher, for example OR 4.42, p<0.001 according to  (which includes factors such as systemic autoimmune disease patients potentially being more careful to avoid exposure). The result therefore suggests a substantial benefit for HC Q, as is also shown in Ferri et al. Adjusting for the difference in baseline risk of systemic autoimmune patients results in RR 0.24. Details of the multivarible analysis in the paper are not provided for assessment, but the analysis may be significantly affected by overfitting and/or multicollinearity. We note that many results in this study differ significantly from other research, for example proton pump inhibitors show OR 0.62, p<0.001 whereas PPIs are classified as "no expected benefit" and other research suggests they increase risk.
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