CXCL11 and influenza: In conclusion, despite antibiotic treatment for bacterial coinfections, critically ill COVID-19 patients maintained very high levels of IL-15, granzyme B, CCL2, CCL7, CCL8, CXCL1, CXCL10, CXCL11, and CXCL12α and the serine protease inhibitors SLPI and elafin in their lungs, whereas after influenza infection these molecules returned to basal levels in the recovery phase.