Although the enrichment analysis on the gene set in cluster 4 of ATAC-Seq showed no significant pathways associated with immune responses, chromatin accessibility at the CXCL13 locus was still increased 28 days after the second vaccination, suggesting that the innate immune memory induced by mRNA vaccines may promote B cell maturation and antibody responses and help develop a rapid host defense against natural infection (41, 42). Here, CXCL13 is linked to infection.