Impacts of delayed influenza vaccination on clinical outcomes in ICU-admitted patients with influenza: A retrospective cohort study

Abstract

Background: Influenza vaccination is an effective measure for reducing the risk of severe influenza infection. However, the task of achieving adequate vaccination rates remains a global challenge. It is unclear whether delayed influenza vaccination is useful for influenza patients. We conducted this study to investigate whether delayed vaccination can reduce mortality in these patients.

Methods: This retrospective cohort study was conducted by reference to the Medical Information Mart for Intensive Care IV (MIMIC-IV) 3.0 database, focusing on patients admitted to the ICU with a diagnosis of influenza. Patients were divided into two groups on the basis of post-admission vaccine use. Propensity score matching (PSM) and inverse probability of treatment weighting (IPTW) were applied to reduce baseline imbalance. The primary outcome was 28-day mortality. Regression analysis and machine learning models, including the Boruta algorithm and LASSO analysis, were used to assess the association between postadmission influenza vaccination use and prognosis results. Sensitivity and subgroup analyses were conducted to evaluate the robustness of the findings.

Results: This study focused on a cohort of 277 influenza patients from 2008 to 2022. Following the implementation of a 1:1 nearest-neighbor PSM procedure, 164 patients were successfully matched. In the PSM cohort, delayed vaccination was not associated with 28-day mortality (Model I: RR, 1.07; 95 % CI, 0.55-2.08; P=0.838; Model II: RR, 0.84; 95 % CI, 0.44-1.61; P = 0.602; Model III: RR, 0.81; 95 % CI, 0.43-1.56; P = 0.534). In the IPTW cohort, the association remained non-significant (Model I: RR, 1.22; 95 % CI, 0.73-2.03; P=0.446; Model II: RR, 1.12; 95 % CI, 0.66-1.91; P=0.662; Model III: RR, 1.17; 95 % CI, 0.72-1.88; P = 0.524). The secondary outcomes, including 60-day mortality, 90-day mortality, ICU mortality and hospital mortality, use of continuous renal replacement therapy and need for mechanical ventilation, remained consistent.

Conclusions: Our study revealed that delayed vaccination did not improve outcomes for critically ill influenza patients, thus highlighting the urgent need for early vaccination to reduce the severity of the disease and protect vulnerable people.

Keywords: Influenza; Intensive care unit; MIMIC-IV; Mortality; Vaccine.