CD4 and hand, foot and mouth disease: As shown in Fig 3 and S1 Table, the results of routine laboratory diagnoses for patients with severe HFMD showed IL-6 levels (SMD = 1.57, 95%CI: 0.55 to 2.60), and neutrophils ratio (SMD = 0.55, 95%CI: 0.17 to 0.93) compared with patients with mild HFMD, but the results displayed reduced CD4+ levels (SMD = -1.38, 95%CI: -2.33 to -0.43), lymphocytes ratio (SMD = -0.48, 95%CI: -0.93 to -0.33) and WBC count (SMD = -0.68, 95%CI: -1.33 to -0.04).