IL6 and COVID-19: In contrast, when compared with patients in the acute phase using seven cohorts from seven studies [13, 34, 37, 38, 44, 46, 48], long COVID-19 patients had lower mean IL-6 levels (mean difference =  − 14.49 pg/ml, 95% CI =  − 24.59 to − 4.39 pg/ml, I2 = 94%, P = 0.005; Fig. 5A).