COVID-19 prophylaxis with doxycycline and zinc in health care workers: a prospective, randomized, double-blind clinical trial.

Objectives: This study aims to assess the efficacy of a combination treatment of doxycycline and zinc in the primary prevention of COVID-19 infection in Tunisian health care workers compared with two control groups.

Methods: We conducted a prospective, randomized, double-blind clinical trial over 5 months to determine the efficacy of a preventive combination treatment dose of doxycycline (100 mg/day) and zinc (15 mg/day), compared with a single-dose treatment with doxycycline versus placebo. The effectiveness of preventive treatment was measured by the significant decline in the number of cases of COVID-19 infection and/or a decrease in the viral load as determined by SARS-CoV-2 cycle threshold value using reverse transcription polymerase chain reaction tests.