The influenza vaccine is one of the best ways to prevent influenza infection, but little is known about influenza vaccine failure.
This study evaluated patients admitted for an acute respiratory illness during the 2015-2019 influenza seasons to compare vaccinated, influenza-negative patients to vaccinated, influenza-positive patients. Statistical analyses were performed with STATA and R using Pearson’s chi-squared, Kruskal-Wallis, Wilcoxon rank-sum tests and multivariate logistic regression.
1236 patients vaccinated for influenza were enrolled, of which 235 (19%) tested positive for influenza. Demographics, vaccines and comorbidities were similar between the groups except for morbid obesity (13% in the influenza negative vs. 8%, p=0.04), and immunosuppression (63% in the influenza positive vs. 54%, p=0.01). Logistic regression analysis demonstrated older patients (OR 1.47, 95%CI 1.03-2.10) and immunosuppressed patients (OR 1.56, 1.15-2.12) were at increased risk for influenza despite immunization. When evaluated by influenza subtype, immunosuppression was found to increase the risk for influenza A/H3N2 (OR 1.86, 95%CI 1.25-2.75).
Our study demonstrated increased risk of influenza vaccine failure in older patients and immunosuppressed patients. These groups are also at increased risk for influenza complications. To improve protection of patients against future influenza illnesses, more effective vaccines and strategies are needed.
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