Factors Associated with Antibiotic Initiation After DaBT-Hib-IPV Vaccination in NICU-Hospitalized Preterm Infants: The Role of C-Reactive Protein.

Objective: The purpose of this study was to evaluate the factors, particularly post-vaccination C-reactive protein (CRP) and the neutrophil-to-lymphocyte ratio (NLR), associated with the clinical decision to initiate antibiotic treatment following the 2-month diphtheria-acellular pertussis-tetanus-Haemophilus influenzae Type B-inactivated poliovirus (DaBT-Hib-IPV) vaccine in hospitalized infants. Methods: A retrospective review was conducted on the medical records of 46 infants. The study included infants hospitalized between 2022 and 2024 at Mersin City Training and Research Hospital who received the 2-month vaccine and subsequently underwent post-vaccination laboratory testing. Infants were categorized based on whether they received antibiotic treatment. Results: Antibiotics were administered to 20 infants, and 26 were observed without any treatment. Despite having a significantly higher gestational age (p = 0.027), the hospital stays of the antibiotic group were significantly longer (median 99 vs. 78 days, p < 0.001). C-reactive protein (CRP) and the neutrophil-to-lymphocyte ratio (NLR) were elevated in the antibiotic group (CRP = 2.82 vs. 1.63 mg/dL, p < 0.001; NLR= 0.90 vs. 0.72, p = 0.041). Culture positivity was low in antibiotic recipients (3/20, 15%). CRP was the only independent predictor of antibiotic administration when adjusted for gestational age and weight at vaccination (Exp(B) = 3.997, p = 0.003). Conclusions: In this cohort of NICU-hospitalized, predominantly preterm infants, a population that does not represent the general population of vaccinated 2-month-old infants, post-vaccination elevations in CRP and NLRs were associated with the clinical decision to initiate antibiotic treatment; however, in the absence of a validated infection reference standard, these markers cannot be assumed to reliably differentiate true infection from vaccine-induced inflammation. To prevent unnecessary antibiotic use and optimize patient management, these markers must be evaluated in conjunction with clinical findings, culture results, and supplementary biomarkers.