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HCQ study #73 of 258
6/29 Pre-Exposure Prophylaxis study (treated before exposed to the virus)
Ferreira et al., J. Medical Virology, July 9, 2020, doi:10.1002/jmv.26286 (preprint 6/29) (Peer Reviewed)
Chronic treatment with hydroxychloroquine and SARS-CoV-2 infection
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Chronic treatment with HCQ provides protection against COVID, odds ratio 0.51 (0.37-0.70).
The actual benefit is likely to be larger becasue research shows that the risk of COVID-19 for systemic autoimmune disease patients is much higher overall. Ferri et al. show OR 4.42, p<0.001 [1], which is the observed real-world risk, taking into account factors such as these patients potentially being more careful to avoid exposure.

Ferreira et al., 6/29/2020, retrospective, database analysis, Portugal, Europe, peer-reviewed, 3 authors.
risk of COVID-19 case, 47.1% lower, RR 0.53, p < 0.001, adjusted per study, odds ratio converted to relative risk.

Effect extraction follows pre-specified rules prioritizing more serious outcomes. For an individual study the most serious outcome may have a smaller number of events and lower statistical signficance, however this provides the strongest evidence for the most serious outcomes when combining the results of many trials.
Details of all 258 studies    Meta analysis
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