Influenza risk concentrates in vulnerable patients

Older age, immune compromise, and chronic illness identify patients at highest influenza risk.
*Systematic review and meta-analysis of observational studies; Level 2 (OCEBM).

Citation

Gao Y, Liu M, Uyeki TM, et al. Risk factors for hospital admission and mortality in patients with influenza virus infection: a systematic review and meta-analysis. Lancet Respir Med. Published online September 8, 2026. doi:10.1016/S2213-2600(26)00195-5

Background

Influenza usually resolves without complications, but some patients require hospital care or die. This review was done to support updated World Health Organization guidance by clarifying which patients with seasonal influenza are at greatest risk.

Patients

2,150,518 patients of any age with laboratory-confirmed seasonal influenza from 63 observational studies. Excluded studies of only pandemic or animal-origin influenza, case-control studies, small studies, and studies without adjusted estimates.

Intervention

Presence of clinical risk factors.

Control

Absence of the same risk factor.

Outcome

Hospital admission among non-severe influenza; all-cause mortality among severe influenza.

Follow-up Period

Varied by study; recruitment years 2005 to 2024.

Results

Patient group Outcome Key factor Adjusted odds ratio
Non-severe influenzaHospital admissionCardiovascular diseaseOR 2.72 (95% CI 1.24 to 5.94)
Non-severe influenzaHospital admissionImmune compromiseOR 2.70 (95% CI 1.55 to 4.70)
Non-severe influenzaHospital admissionChronic respiratory diseaseOR 2.24 (95% CI 1.90 to 2.64)
Severe influenzaDeathSecondary bacterial infectionOR 4.13 (95% CI 1.53 to 11.14)
Severe influenzaDeathSepsisOR 3.19 (95% CI 2.08 to 4.89)
Severe influenzaDeathAge 65 years or olderOR 2.47 (95% CI 2.21 to 2.75)

OR=odds ratio; CI=confidence interval.

Analyses used adjusted study estimates. Results were consistent after excluding pandemic-era studies and studies with higher bias risk.

Limitations

Evidence was observational, so unmeasured confounding remains possible. Some risk factors relied on few studies, definitions varied, children were underrepresented, and results mainly reflect adult populations in Europe, North America, and Asia.

Funding

WHO and Chinese public grants; no reported funder role.

Clinical Application

Prioritize vaccination, early antivirals, and closer monitoring for influenza patients with these high-risk features.