“Long COVID, or post-acute COVID syndrome (PACS), is now estimated to occur in 19% of adults having presented with COVID-19.. PACS is believed to be caused by immunological changes that persist after acute infection. Furthermore, it is now increasingly recognized that these changes include not only those in the adaptive immune system, such as production of autoantibodies or autoreactive T cells due to molecular mimicry, but also those in the innate immune system.. A new study by Cheong et al. in Cell reveals crucial differences in the transcriptional and epigenetic state of innate immune cells and their progenitors [among PASC patients].. the study team demonstrated that myeloid cells and hematopoietic progenitor cells harbored transcriptional and chromatin accessibility changes that did not return to baseline even 1 year after acute SARS-CoV-2 infection. These data provide powerful evidence that persistent changes (i.e., trained immunity) may underlie PACS..”