Survey of 319 autoimmune disease patients taking C
Q with 5.3% COVID-19 incidence, compared to a control group from the general population (matched on age, sex, and region, but not adjusted for autoimmune disease), with 3.4% incidence.
It not clear why authors did not compare with autoimmune patients not on C
Q. Other 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 , which is the observed real-world risk, taking into account factors such as these patients potentially being more careful to avoid exposure. If we adjust for the different baseline risk, the result becomes RR 0.36, p<0.001, suggesting a substantial benefit for HC
Q treatment (as shown in other studies).
There may also be significant survey bias - those experiencing COVID-19 may be more likely to respond to the survey.
Authors note that they "could not eliminate completely the possibility of some bias due to the intrinsic condition of the individuals within the treatment group that are undergoing ch
loroquine or derivative drug treatment due to other diseases that alter their health status and may have different comorbidities", however they could account for one significant bias by comparing with matched autoimmune disease patients.