2732. Estimate of the Effectiveness of Influenza Vaccine among Children for the 2017–2018 Season

BACKGROUND: The 2017–2018 influenza season was one of the deadliest in decades, with 180 pediatric deaths, 80% among children who did not receive the vaccine. Circulating influenza strains change periodically, making it important to determine vaccine efficacy on an annual basis specifically in susceptible populations. The primary aim of our study was to estimate the effectiveness of the influenza vaccine for the 2017–2018 season. Secondary aims were to determine effect of weaning immunity and of previous season vaccination. METHODS: Children 6 months to 17 years tested for influenza during the 2017–2018 season at Children’s Hospital of New Orleans were included. Clinical charts were reviewed, and immunization status confirmed via the Louisiana Immunization Registry. Using a multivariable logistic regression model vaccine effectiveness (VE) was estimated by comparing vaccination status of influenza-positive vs. influenza-negative cases with the formula VE = (1 − OR) × 100%. RESULTS: 4,825 children were included; 22% of them tested positive for influenza, mostly influenza A (61.9%); 21% had received an influenza vaccine prior to illness: 14% among the influenza-positive and 23% among influenza-negative (P < 0.0001). Overall, VE for the 2017–2018 influenza season was 43% (95% CI 30, 53); 44% for influenza A and 38% for influenza B. While receiving current year (2017–2018) vaccine had the most effect, receiving the previous year (2016–2017) vaccine had additional benefit. We found no waning immunity of the vaccine for the 2017–2018 season. CONCLUSION: Influenza VE was modest for children in the local area of New Orleans and similar to the CDC’s findings for the nation as a whole. Previous year vaccination had a small, but significant benefit and there was no evidence of waning immunity in our cohort. Ongoing national and local surveillance is important to understand the benefit of influenza vaccination. DISCLOSURES: All authors: No reported disclosures.