2756. Pragmatic Assessment of Influenza Vaccine Effectiveness in the DoD (PAIVED), Influenza-Like-Illnesses (ILIs) Sub-Study at the Marine Corps Recruit Depot-San Diego, CA (MCRD-SD) During the 2018–2019 Influenza Season

Abstract Background Military recruits suffer high rates of influenza and influenza-like illness (ILI) during training. ILIs may lead to morbidity, lost training time, and hospitalization. We evaluated the incidence and clinical outcomes of ILI among recruits at Marine Corps Recruit Depot San Diego (MCRD-SD) in a prospective trial of influenza vaccine efficacy. Methods Recruits at MCRD-SD were enrolled to compare the effectiveness of 3 types of FDA approved influenza vaccine: Afluria®, an egg-based vaccine; Flucelvax®, a cell-culture-derived vaccine; and Flublok®, a recombinant vaccine. Four companies of recruits were enrolled sequentially from 28 November 2018 to 19 December 2018, then randomized in a 1:1:1 ratio. Participants were followed for 18 weeks at MCRD-SD and Camp Pendleton. All participants who presented with ILI symptoms at medical care sites underwent viral diagnostic testing in addition to immunologic studies. Recruits were excluded from participation if <18 years of age, if previously vaccinated in the 2018–2019 season, or if reporting allergy to the vaccines. Results Of 1338 recruits approached, 771 (57.6%) participants consented for enrollment. All recruits were men between 18 and 28 years. There were 182 ILIs amongst 177 recruits (23% of 771 recruits). Nasal swabs were obtained in 180/182 cases (99%). Mean duration of ILI symptoms was 7 days. Mean days of fever was 4. Subjects reported a total 168 days of reduced training (range 0–14 days; mean 0.9 days). There were 47 total days of missed training for all subjects (range of 0–4 days; mean 0.3 days/subject). There were no hospitalizations related to ILIs. Approximately 82% (148/182) of ILIs presented within the first 3 weeks of training; 44% (80/182) of ILIs occurred during the second week of training. PCR- nasal swabs results; race/ethnicity data, and frequency of ILI mapped to week of training are illustrated below. Conclusion ILIs can negatively impact training effectiveness. Days lost to training from ILIs and hospitalizations can prevent successful completion of training with impact on military readiness. PAIVED may inform the DoD on future strategies to minimize influenza and other respiratory threats in recruit military populations. Influenza vaccine effectiveness will be reported separately. Disclosures All authors: No reported disclosures.