Objective - This work was undertaken to evaluate the protective effect of Arsenicum album 30C against COVID-19. Design - The work was designed as a prospective parallel cluster cohort study. Intervention - Participants were enrolled in a homeopathy intervention (HI) cohort (who received Arsenicum album) or in a non-intervention (NI) cohort (who received no systematic intervention) from COVID-19 containment areas of Delhi. Individuals of age 5 years or above were given four medicated pills of Arsenicum album 30C, while those from 1 to 5 years old were given two medicated pills in each dose. Results - The analysis included 10,180 individuals residing in 11 COVID-19 containment areas in Delhi, out of which 6,590 individuals were in the HI cohort and 3,590 individuals were in the NI cohort. The overall protective effect of Arsenicum album 30C was 83.43% (95% confidence interval [CI], 76.77 to 88.17): 45 cases per 6,590 (8.34 per 10,000 person-weeks) in the Arsenicum album 30C group versus 143 cases per 3,590 (45.01 per 10,000 person-weeks) in the NI cohort. The protective effect of Arsenicum album 30C against laboratory confirmed COVID-19 was 74.40% (95% CI, 55.08 to 85.41): 18 cases per 6,590 (3.32 per 10,000 person-weeks) in the Arsenicum album 30C group versus 38 cases per 3,590 (11.85 per 10,000 person-weeks) in the NI cohort. Conclusion – The   use of Arsenicum album 30C was associated with some protection against probable and laboratory-confirmed COVID-19 in a containment-zone setting. Randomized controlled trials are needed to confirm or refute these results.