1328. Risk Factors for Severe Influenza Outcomes Among Infants Born Between 2011 and 2019

BACKGROUND: Influenza in infancy can cause significant morbidity and mortality. This study aimed to characterize influenza outcomes in infants < ορ = 12 months and identify risk factors for severe infection. METHODS: A retrospective cohort of infants ≤ 12 months born between 2011-2019 who received longitudinal ambulatory and inpatient care within a multi-facility hospital system and had laboratory-confirmed influenza were included. Perinatal, medical and illness characteristics were described. Risk factors for severe influenza (hospitalization, intensive-care unit (ICU) admission, secondary bacterial infections) were analyzed using Chi-square analysis and multivariate logistic regression. RESULTS: Among 421 infants with influenza, 134 (32%) were < 6 months (m), 28 (6.5%) were born prematurely (< 35 weeks gestational age), and 41(10%) had chronic medical conditions (CMC). 62 (15%) required hospital admission, 13 (21%) of which required ICU care. No deaths were reported. Secondary bacterial infections were diagnosed in 101 (24%) including acute otitis media (84%), pneumonia (15%) and sinusitis (3%). Prematurity (OR 3.6, 95%CI:1.5-8.3), age < 6m (OR 3.4, 95%CI:1.9-5.9), and CMC (OR 7.6, 95%CI 3.8-15.3) were significantly associated with hospitalization. Prematurity, age < 6m, and CMC were also associated with ICU admission. Infants > 6m (OR 2, 95%CI:1.2-3.5) were more likely to be diagnosed with a secondary bacterial infection than younger infants. Among infants > 6m, complete influenza vaccination (2 doses) was associated with lower rates of antibiotic use (OR 0.5, 95% CI:0.3-0.9) compared to partial or no vaccination, but did not significantly affect hospitalization, ICU admission, or frequency of secondary bacterial infections. Adjusting for prematurity, age < 6m remained associated with hospitalization (aOR 4, 95%CI: 2.1-7.3) as did presence of CMC (aOR 7.3, 95%CI 3.3- 15.7). For ICU admission, age < 6m (aOR 6.3, 95%CI:1.6-24.1) and CMC (aOR 19.7,95%CI:4.9-79.5) were also independent risk factors. CONCLUSION: Younger age and chronic medical conditions were independent risk factors for severe influenza infection. Complete influenza vaccination in eligible age groups was associated with decreased antibiotic use. DISCLOSURES: John V. Williams, MD, GlaxoSmithKline (Advisor or Review Panel member, Independent Data Monitoring Committee)Quidel (Advisor or Review Panel member, Scientific Advisory Board) Judith M. Martin, MD, Merck Sharp and Dohme (Consultant)