Influenza Vaccination Status and Clinical Outcomes Among Adults Hospitalized with Community-Acquired Pneumonia: A Retrospective Cohort from Saudi Arabia

Background: Influenza vaccination is widely recommended to prevent influenza and its complications; however, its association with clinical outcomes among high-risk populations remains uncertain. This study aimed to investigate the association between influenza vaccination status and clinical outcomes among adults hospitalized with community-acquired pneumonia (CAP) in Saudi Arabia. Methods: This retrospective cohort study included adults hospitalized with CAP in Saudi public hospitals between October 2023 and March 2024. Data on demographic characteristics, comorbidities, influenza vaccination status, laboratory-confirmed influenza infection, intensive care unit (ICU) admission, in-hospital mortality, and length of hospital stay were obtained from electronic health records. Logistic regression analyses were performed to evaluate the associations between influenza vaccination and clinical outcomes. Results: Among 485 patients, 114 (23.5%) had received the seasonal influenza vaccine. The prevalence of laboratory-confirmed influenza infection was similar among vaccinated and unvaccinated patients (57.9% vs. 58.5%, p-value = 0.910). Vaccinated patients were less likely to require ICU admission (1.8% vs. 7.5%, p-value = 0.025), while no significant differences were observed in length of hospital stay or in-hospital mortality. After adjustment for age, sex, and comorbidities, influenza vaccination was associated with lower odds of ICU admission (OR = 0.200, 95% CI: 0.045, 0.894). No significant associations were observed between influenza vaccination and laboratory-confirmed influenza infection, length of hospital stay, or in-hospital mortality. Conclusions: Among adults hospitalized with CAP in Saudi Arabia, influenza vaccination was associated with a lower likelihood of ICU admission, supporting its potential role in reducing disease severity among high-risk populations.