IL6 and COVID-19: The level of IL-6 in long COVID-19 patients was higher than that in healthy individuals, whether the mean values were given directly by the studies (mean difference = 12.42 pg/ml, 95% CI = − 2.43 to 27.28, P = 0.10) or obtained from the medians (mean difference = 5.92 pg/ml, 95% CI = 3.12–8.72, P < 0.0001).