Influenza: WHO-commissioned review grades the risk factors for admission and death

Design

Systematic review and meta-analysis of observational studies, GRADE assessed

Population

63 studies, 2,150,518 patients with laboratory-confirmed seasonal influenza

Primary outcome

Hospital admission (non-severe); all-cause mortality (severe)

Effect

Admission: CVD OR 2.72, immunosuppression 2.70; death: bacterial co-infection OR 4.13, malnutrition 3.29

A systematic review for the WHO influenza guideline pooled 63 observational studies with adjusted estimates, covering 2.15 million patients with laboratory-confirmed seasonal influenza, and graded certainty with GRADE.

In non-severe influenza, moderate-to-high certainty risk factors for admission were cardiovascular disease (OR 2.72), immunosuppression including HIV (2.70), neurological disease (2.31), chronic respiratory disease (2.24), each decade of adult age (1.72), pregnancy (1.88), diabetes (1.84) and cancer (1.75). In severe influenza, the strongest risk factors for death were secondary bacterial infection (4.13), malnutrition (3.29), sepsis (3.19), acute kidney injury (2.92) and age 65 or over (2.47).

The list largely confirms who should be offered early antivirals and vaccination. The mortality factors are the useful addition for inpatient teams: bacterial co-infection, malnutrition and kidney injury identify patients to escalate early. Malnutrition, relevant to many Indian inpatients, appears as a strong predictor.

• Offer early antiviral treatment to outpatients with any listed risk factor
• Vaccinate pregnant women, people with chronic heart, lung, neurological or kidney disease, and the immunosuppressed
• In admitted patients, look actively for bacterial co-infection and treat it
• Assess nutritional status and kidney function on admission
• Escalate early when sepsis or acute kidney injury develops

Why it matters

It gives a graded evidence base for triage decisions that are often made on instinct.

Don't overread it

These are observational associations; they identify who is at risk, not that treating a risk factor lowers mortality.

The statistics, in plain English

Odds ratios here are adjusted for other factors, so each estimates the independent association. Wide intervals, such as 1.53 to 11.14 for bacterial co-infection, mean the size is uncertain even if the direction is clear. GRADE certainty reflects how confident the reviewers are in each estimate, not how strong the effect is.

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