Keigai-rengyo-to as post-exposure prophylaxis for severe acute respiratory syndrome coronavirus 2 infection

Background: Effective prevention against COVID-19 is urgently required to control vaccine breakthrough infection. Laboratory and clinical data suggested that Keigai-rengyo-to (KRT) performs biological activity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We investigated whether KRT could prevent SARS-CoV-2 in medical personnel exposed to patients with COVID-19.Methods: We conducted an open-label controlled clinical trial of medical personnel after COVID-19 vaccination at our hospital (ClinicalTrials.gov: UMIN000048389). Participants were close contacts recently exposed (<72 h) to patients with COVID-19. We provided the participants with KRT (7.5 g/day for 5 days) or no drug as a control. The primary endpoint was nicking endonuclease amplification reaction or polymerase chain reaction confirming incident SARS-CoV-2 infection. Safety was assessed in all treated participants.Results: Between January and September 2022, 38 close contacts were assigned: 20 to the KRT group and 18 to the control group. During 2 weeks of follow-up, 10/38 (26%) participants had new-onset COVID-19. The incidence of COVID-19 was significantly lower in the KRT group (2/20; 10%) than in the control group (8/18; 44%), with a medium effect size (p < 0.05; phi coefficient = -0.391; total absolute risk reduction: 34.4% points). The number needed to treat to prevent the occurrence of a COVID-19 case was 2.9. The overall relative risk was 0.23 (95% confidence interval: 0.06-0.78). No serious safety problems were detected.Conclusion: Post-exposure prophylaxis with KRT can prevent the onset of COVID-19 in close contacts after vaccination. More randomized clinical trials with larger samples are required to better evaluate KRT as a post-exposure prophylaxis of SARS-CoV-2.(c) 2023 The Japanese Respiratory Society. Published by Elsevier B.V. All rights reserved.