1512. Influenza vaccine effectiveness wanes over the influenza season: results from five military treatment facilities

BACKGROUND: Influenza vaccination can reduce influenza burden, but questions have arisen about the duration of vaccine protection. While the timing of vaccination varies, annual receipt of influenza vaccine is mandated for active duty military personnel. The goal of this analysis is to determine if influenza vaccine effectiveness decreases over time. A secondary goal of this analysis is to determine if repeated influenza vaccination is associated with risk for influenza. METHODS: Otherwise healthy individuals presenting for treatment of acute respiratory infections at 5 military treatment facilities from 2009 to 2018 were enrolled in the Acute Respiratory Infection Consortium (ARIC) study. Individuals with complete demographics, influenza vaccination in the two years prior to illness, and influenza laboratory results were included in this analysis (n=1,273). Multivariate logistic regression was used to calculate the odds of an influenza diagnosis according to time since influenza vaccination, categorized in 90-day periods. The model also included age, race, month of diagnosis, influenza season, and whether the participant received 4+ influenza vaccinations in the past 5 years. RESULTS: One hundred and ninety-two individuals (15%) had laboratory confirmed influenza (Table 1). Participants were mostly active duty, male, and white. Over half of the participants received 4+ influenza vaccinations in the past 5 years. Participants who were vaccinated 90-179 and 180+ days ago had greater odds of being diagnosed with influenza than did individuals who were vaccinated < 90 days prior to illness onset (Table 2). Participants who were 18-24 years old had lower odds of influenza than individuals in other age groups. Vaccine experience (vaccinated against influenza for at least four of the past five years), race, and ethnicity were not statistically significantly associated with influenza diagnosis. Table 1. Characteristics of individuals included in the analysis of waning influenza vaccine effectiveness in the ARIC study [Image: see text] Table 2. Multivariate logistic regression results from model using influenza diagnosis as the outcome variable. Also included in the model are season and month of diagnosis. [Image: see text] CONCLUSION: Influenza vaccination was most effective 14-89 days post-vaccination and effectiveness decreased thereafter. Repeat influenza vaccination, however, was not significantly associated with greater odds of influenza. The waning effectiveness of influenza vaccination indicates additional consideration be given to the timing of vaccination. Disclaimer [Image: see text] DISCLOSURES: All Authors: No reported disclosures