C3 and COVID-19: The complement components C1q, C3, complement regulator factor D, factor I, and activation product C3b/iC3b exhibited associations with lymphocytes, C-reactive protein, and sodium levels, respectively, which have been described as markers associated with the prognosis of MIS-C and acute COVID-19.13 These results highlight the possible association of the complement system with the disease severity of MIS-C and COVID-19 in children.