Likewise, when compared with the non-PASC group using four relevant cohorts from three studies [43, 45, 47], long COVID-19 patients had higher mean IL-6 levels (mean difference = 3.32 pg/ml, 95% CI = 0.22–6.42 pg/ml, I2 = 88%, P = 0.04; Fig. 4B). This evidence concerns the gene IL6 and COVID-19.