1161. Effectiveness of the Influenza Vaccine for Preventing Laboratory-Confirmed Influenza Infections in Outpatient Immunocompromised Adults, 2017-2018

Abstract Background While the number of immunocompromised (IC) individuals continues to rise, the existing literature on influenza vaccine effectiveness (VE) in IC populations is limited. IC individuals have a higher risk of severe influenza and influenza-related hospitalizations, and understanding the VE of the seasonal influenza vaccines in IC populations remains paramount. Methods Using 2017-2018 US Flu VE Network (US Flu VE) data, we examined the VE of the 2017-2018 seasonal influenza vaccine against symptomatic influenza in outpatient settings among IC adults. Patients were enrolled from outpatient sites in five states. IC status was determined by ICD-10 codes. We used logistic regression and adjusted for enrollment site, race, self-reported general health status, age, and onset date of symptoms. Separate models were used to calculate and compare the VE for non-IC and IC among outpatient adults >18 years. Results 5671 participants were included in the adult analytic dataset, and 455 (8%) were IC. The VE among non-IC was 31% (95% CI: 22, 39) and among IC participants was -4 % (95% CI: -66, 35). P-value for interaction by IC status was 0.100. Conclusion We observed lower VE against symptomatic influenza among non-hospitalized patients with immunocompromising conditions though the difference was not statistically significant. This study demonstrates the capacity to study a large IC population using an existing influenza VE network and contributes to the literature to support large, multicenter VE studies for IC populations. Disclosures Richard K. Zimmerman, MA; MD; MPH; MS, Sanofi Pasteur: Grant/Research Support MaryPatricia Nowalk, PhD, RDN, Merck & Co.: Grant/Research Support|Merck & Co.: Honoraria|Sanofi: Grant/Research Support Fernanda P. Silveira, MD, Ansun: Grant/Research Support|Eurofins Viracor: Advisor/Consultant|Janssen: Advisor/Consultant|Merck: Grant/Research Support|Regeneron: Grant/Research Support|Takeda: Advisor/Consultant Emily T. Martin, PhD, MPH, Merck: Grant/Research Support