Abstract: medRxiv preprint doi: https://doi.org/10.1101/2021.05.14.21257059; this version posted May 16, 2021. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. All rights reserved. No reuse allowed without permission. Hydroxychloroquine For Prophylaxis Of COVID-19 In Health Workers: A Randomized Clinical Trial. AUTHORS: Jorge Rojas-Serrano, Angelica Margarita Portillo-Vásquez Ireri Thirion-Romero, Joel Vázquez-Pérez, Fidencio Mejía-Nepomuceno Alejandra Ramírez-Venegas, Karla Midori Pérez-Kawabe, Rogelio Pérez-Padilla. On behalf of the RESEARCH GROUP ON HYDROXYCHLOROQUINE FOR COVID-19 also formed by Dr. Cristobal Guadarrama, Dr. Carmen Margarita Hernández Cárdenas, Dr. Luis Felipe Jurado Camacho Dr. Sebastián Rodríguez Llamazares, Dra. Alejandra Ramírez Venegas ACKNOWLEDGMENTS: FUNDING Support for the trial was received from the Instituto Nacional de Enfermedades Respiratorias (INER), from CONACYT (national council of science and technology) and by SANOFI-AVENTIS through an investigator-sponsored trial. Neither the INER, CONACYT or SANOFI AVENTIS had role in the des ign of the study, collection of data, analysis, results interpretation, the writing of the final report and the decision to submit the article to publication. NOTE: This preprint reports new research that has not been certified by peer review and should not be used to guide clinical practice. medRxiv preprint doi: https://doi.org/10.1101/2021.05.14.21257059; this version posted May 16, 2021. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. All rights reserved. No reuse allowed without permission. SUMMARY Health care workers are at high risk of being infected with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV2). Our aim is to evaluate the efficacy and safety of hydroxychloroquine (HCQ) for prophylaxis of COVID19 in health personnel exposed to patients infected by SARS-COV-2. Methods: Double-blind randomized, placebo-controlled single center clinical trial. Included subjects were health care workers caring for severe COVD19 patients. Main outcome was time to symptomatic SARS-CoV2 infection. Results: 127 subjects with a confirmed baseline negative RT-PCR SARS-CoV2 test were included in the trial, 62 assigned to HCQ and 65 to placebo. One subject (1.6%) in the HCQ group and 6 (9,2%) subjects in the placebo group developed COVID-19. (Log Rank test p = 0.09). No severe COVID19 cases were observed. The study was suspended because of a refusal to participate and losses to follow up after several trials reported lack of effectiveness of hydroxychloroquine in hospitalized patients with COVID-19. CONCLUSION Although the number of symptomatic infections in health personnel was lower in the HCQ group, the difference was not statistically significant. The trial is underpowered due to the failure to complete the estimated sample size. Key words: COVID-19, health workers, prophylaxis, hydroxychloroquine, medRxiv preprint doi: https://doi.org/10.1101/2021.05.14.21257059; this version posted May 16, 2021. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. All rights reserved. No reuse allowed without..