Abstract
Background: Influenza vaccine effectiveness (VE) against a spectrum of severe disease, including critical illness and death, remains poorly characterized. Methods: We conducted a test-negative study in an intensive care unit (ICU) network at 10 US hospitals to evaluate VE for preventing influenza-Associated severe acute respiratory infection (SARI) during the 2019-2020 season, which was characterized by circulation of drifted A/H1N1 and B-lineage viruses. Cases were adults hospitalized in the ICU and a targeted number outside the ICU (to capture a spectrum of severity) with laboratory-confirmed, influenza-Associated SARI. Test-negative controls were frequency-matched based on hospital, timing of admission, and care location (ICU vs non-ICU). Estimates were adjusted for age, comorbidities, and other confounders. Results: Among 638 patients, the median (interquartile) age was 57 (44-68) years; 286 (44.8%) patients were treated in the ICU and 42 (6.6%) died during hospitalization. Forty-five percent of cases and 61% of controls were vaccinated, which resulted in an overall VE of 32% (95% CI: 2-53%), including 28% (-9% to 52%) against influenza A and 52% (13-74%) against influenza B. VE was higher in adults 18-49 years old (62%; 95% CI: 27-81%) than those aged 50-64 years (20%;-48% to 57%) and ≥65 years old (-3%; 95% CI:-97% to 46%) (P=.0789 for interaction). VE was significantly higher against influenza-Associated death (80%; 95% CI: 4-96%) than nonfatal influenza illness. Conclusions: During a season with drifted viruses, vaccination reduced severe influenza-Associated illness among adults by 32%. VE was high among young adults.
Original language | English (US) |
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Pages (from-to) | 1459-1468 |
Number of pages | 10 |
Journal | Clinical Infectious Diseases |
Volume | 73 |
Issue number | 8 |
DOIs | |
State | Published - Oct 15 2021 |
Keywords
- critical illness
- immunization
- influenza
- vaccination
- vaccine effectiveness
ASJC Scopus subject areas
- Microbiology (medical)
- Infectious Diseases