Effectiveness of influenza vaccination to prevent severe disease: a systematic review and meta-analysis of test-negative design studies
Bibliographic record
Abstract
BACKGROUND: Seasonal influenza vaccination may be effective against severe influenza disease. OBJECTIVES: To assess evidence on the real-world effectiveness of influenza vaccination in preventing severe influenza-related outcomes. METHODS: Data sources: PubMed, Ovid, and Cochrane CENTRAL from inception to September 24, 2024. STUDY ELIGIBILITY CRITERIA: Observational test-negative design studies reporting influenza vaccine effectiveness (IVE) against influenza-associated hospitalisation, death, pneumonia, intensive care unit admission, or ventilatory support. PARTICIPANTS: Hospitalized adults and children with laboratory-confirmed influenza and inpatient controls who tested negative for influenza infection. INTERVENTIONS: Influenza vaccination. ASSESSMENT OF RISK OF BIAS: Newcastle-Ottawa Scale and Grading of Recommendations Assessment, Development, and Evaluation were used to assess study quality and evidence certainty. METHODS OF DATA SYNTHESIS: We extracted study characteristics and ORs or IVE estimates and corresponding 95% CI. Both crude and adjusted estimates were considered and analysed using a random-effects model. We calculated the pooled IVE overall and by season, age group, circulating strains, vaccine type, and match between the vaccine and circulating strains. RESULTS: Overall, 7727 publications were identified, 461 reviewed, and 165 included. Pooled IVE was 42% (95% CI: 39-44) against influenza-associated hospitalisation (very low certainty), 36% (95% CI: 24-46) against death (no certainty), 51% (95% CI: 36-63) against pneumonia (low certainty), 52% (95% CI: 38-63) against intensive care unit admission (very low certainty), and 55% (95% CI: 44-64) against ventilatory support (low certainty). IVE varied by age and was generally higher (up to 2-fold) in children compared to adults. Higher IVE was observed against influenza A(H1N1) compared to A(H3N2) and in seasons with good vaccine match. Hospitalisation IVE was slightly higher for quadrivalent (45% (95% CI: 32-56)) compared to trivalent (36% (95% CI: 27-43)) vaccine. CONCLUSIONS: Seasonal influenza vaccination moderately reduces severe influenza-related outcomes, particularly in children, against A(H1N1), and with a good vaccine-strain match. PROSPERO REGISTRATION: CRD42023476003.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.017 | 0.037 |
| Meta-epidemiology (narrow) | 0.003 | 0.002 |
| Meta-epidemiology (broad) | 0.024 | 0.040 |
| Bibliometrics | 0.004 | 0.004 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.003 | 0.002 |
| Open science | 0.003 | 0.002 |
| Research integrity | 0.003 | 0.003 |
| Insufficient payload (model declined to judge) | 0.004 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".