Human coronavirus data from four clinical trials of masks and respirators

•We reviewed seasonal coronavirus data from four randomized clinical trials of face masks and respirators.•Data from a community trial showed no transmission of seasonal coronaviruses from infected children to parents who wore a mask.•Data from healthcare worker randomized clinical trials showed a four-fold lower rate of coronavirus infections in people wearing an N95 respirator compared to surgical masks, but this difference was not significant.•Data from a clinical trial of mask use by infected patients did not show any transmission of coronaviruses from the sick individual to family contacts. There are few published data on the efficacy of masks or respirators against coronavirus infections. This is an important research question to inform the response to the COVID-19 epidemic. The transmission modes of human coronaviruses are similar, thought to be by droplet, contact, and sometimes airborne routes. There are several randomized clinical trials of masks and respirators, but most used clinical endpoints or tested only for influenza. In four trials that we conducted, we tested for human coronaviruses, but only composite viral endpoints were reported in the trials. We reviewed and analyzed the coronavirus data from four of our trials. Laboratory-confirmed coronavirus infections were identified in our community household trial (one case), health worker trials (eight cases), and trial of mask use by sick patients (19 cases). No coronavirus infections were transmitted in households to parents who wore P2 or surgical masks, but one child with coronavirus infection transmitted infection to a parent in the control arm. No transmissions to close contacts occurred when worn by sick patients with coronavirus infections. There was a higher risk of coronavirus infection in HCWs who wore a mask compared to a respirator, but the difference was not statistically significant. These are the only available clinical trial data on coronavirus infections associated with mask or respirator use. More clinical trials are needed to assess the efficacy of respiratory protection against coronavirus infections.