FNC treatment in viral (+) monkeys increased the levels of IL-4, IL-10, and IL-13 in the thymus, but not of IL-1β, INF-γ, TNF-α, and IL-6, suggesting a biological response against cytokine storm.38–45 Thus, we assume that the high efficiency of FNC in treating COVID-19 may be mediated via at least two steps: antiviral action in the thymus and subsequent promotion of immunity against viral infection for the entire body. Here, IL13 is linked to viral infectious disease.