CCL2 and COVID-19: In our cohort, we compared two types of vaccines and demonstrated that inactivated COVID-19 vaccines trained human monocytes to a regulatory phenotype, mediated by histone modifications in the IL6 and IL10 genes, whereas the non-replicating viral vector COVID-19 vaccine drove human monocytes to a regulatory phenotype, mediated by histone modifications in the IL6, IL10, TNF, and CCL2 genes.