During the outbreak of COVID-19, some DMARDs were recommended for the treatment of COVID-19, and the results of a small randomized controlled trial showed that the level of C-reactive protein (CRP) in 5 COVID-19 patients was significantly lower after receiving treatment with leflunomide, and inflammation was controlled, thus preliminarily confirming the efficacy of leflunomide in treating COVID-19 (26). Here, CRP is linked to COVID-19.