For a study, it was determined that influenza vaccines provided benefits in addition to the direct effect; however, the effect was minimal in the trial. Exceptions notwithstanding, the purpose of global vaccine recommendations should remain the provision of verifiable, direct protection to those who have been vaccinated. From November 2016 to August 2019, researchers looked at the prevalence of fluoroquinolone-resistant Enterobacterales(FQRE) colonization among patients undergoing hematopoietic cell transplantation (HCT) and compared the risk of gram-negative bloodstream infection (BSI) between FQRE-colonized and non colonized individuals. During neutropenia, all patients were given levofloxacin prophylaxis. Stool samples were taken at admission for HCT and weekly until neutropenia was recovered and subjected to FQRE selective culture. Antimicrobial susceptibility testing was performed on all isolates using broth microdilution. Whole-genome sequencing was also performed on FQRE isolates. FQRE was colonized in 54 of 234 (23%) patients prior to HCT, including 30 of 119 (25%) allogeneic HCT recipients and 24 of 115 (21%) autologous HCT recipients. FQRE colonization was linked to recent antibiotic use (P=.048). In addition, 91% of colonizing FQRE isolates were E. coli, and 29% generated extended-spectrum -lactamases. Only 2 of 180 (1.1%) patients who were not colonized with FQRE on admission had gram-negative BSI, compared to 17 (31%) FQRE-colonized patients who acquired gram-negative BSI despite levofloxacin prophylaxis (P=.001). FQRE isolates that were genetically identical to the colonizing strain caused 15 (88%) of the 17 gram-negative BSIs in FQRE-coloniSed patients. While receiving levofloxacin prophylaxis, nearly one-third of HCT patients with pre-transplant FQRE colonization developed gram-negative BSI, with infections caused primarily by their colonizing strains. On the other hand, Levofloxacin prophylaxis was highly successful in patients who were not previously infected with FQRE.