How many people in hospital with flu had the flu vaccine
Executive summary
Recent surveillance and effectiveness studies show that a minority of hospitalized flu patients had been vaccinated in Southern Hemisphere analyses (15.9% vaccinated among hospitalized cases) and vaccine effectiveness (VE) against hospitalization often ranged roughly 34–57% depending on age and network (example: 38%–57% in adults ≥65) [1] [2]. U.S. and Southern Hemisphere reports agree vaccines cut hospitalizations substantially but many hospitalized people remain unvaccinated [3] [2].
1. What the data say: proportion of hospitalized flu patients who were vaccinated
Interim Southern Hemisphere surveillance pooled by CDC and partners found that only 15.9% of hospitalized flu patients (SARI cases) had received the season’s vaccine at least 14 days before illness onset; the same analysis reported 21.3% vaccination among outpatients with influenza-like illness (ILI) [1]. U.S.-focused VE networks report detailed counts of vaccinated and unvaccinated patients used to estimate VE, but public summaries emphasize that many hospitalized influenza patients were not vaccinated, and vaccination status is a core variable in those analyses [2] [4].
2. How to read that proportion: test-negative design and “vaccinated” definition
VE studies cited use a test-negative case-control design and count a patient as vaccinated if they received the seasonal vaccine ≥14 days before symptom onset; those vaccinated <14 days before illness were excluded [2]. That methodological choice means the reported percentages of vaccinated hospitalized people reflect a specific, publicly defensible definition and are not raw counts of any prior vaccination [2].
3. Vaccine effectiveness against hospitalization: substantial but imperfect protection
Interim VE estimates show the vaccine reduces odds of influenza-associated hospitalization by roughly one-half in pooled Southern Hemisphere data (adjusted VE ≈49.7% against hospitalization) and variable protection in U.S. networks—examples include 38% and 57% VE against hospitalization among adults ≥65 in different U.S. networks [3] [2]. Those VE figures explain why vaccinated people still appear among hospitalized cases: a vaccine that is 50% effective cuts risk but does not eliminate it [3] [2].
4. Why some hospitalized patients were vaccinated: age, comorbidity, and exposure
VE is typically lower among older adults and can be lower when circulating strains shift; Southern Hemisphere data show lower VE in older adults (about 37.7%) versus higher VE in children and people with comorbidities in some analyses [3]. That means older or medically vulnerable vaccinated people still face meaningful residual risk of severe disease and hospitalization [3].
5. Vaccine coverage matters: many hospitalizations occur among the unvaccinated
Reports emphasize falling vaccination uptake in some groups (for example, flu vaccination in U.S. children and adults ≥65 had declined compared with pre‑COVID rates) and low proportions vaccinated among hospitalized cases in surveillance datasets imply that low coverage contributes to high hospitalization totals overall [5] [1]. Public-health messaging ties rising hospital burdens to both viral dynamics and vaccination gaps [5].
6. Competing perspectives and limitations in the reporting
Surveillance estimates vary by geography, season, and methodology. Southern Hemisphere pooled data (8 countries) give one set of numbers, while U.S. VE networks (VISION, IVY, US Flu VE) give somewhat different age‑specific VE estimates—VE estimates range across networks [3] [2]. Available sources do not mention a single unified U.S. national percentage of hospitalized flu patients who had been vaccinated for the 2024–25 season; instead, reporting focuses on VE estimates and vaccination percentages within surveillance networks (not found in current reporting).
7. What this means for individuals and policy
Taken together, the data show vaccination substantially reduces the risk of hospitalization (often by roughly half), yet some vaccinated people—particularly older adults and those with comorbidities—will still be hospitalized when transmission is high [3] [2]. Public-health authorities emphasize boosting coverage and using antivirals to reduce severe outcomes in tandem with vaccination [6].
8. Bottom line and unanswered questions
The concrete figure available from pooled Southern Hemisphere surveillance is that 15.9% of hospitalized influenza cases were vaccinated [1]; U.S. network reports document VE estimates and vaccination proportions within their surveillance cohorts but do not provide a single national hospitalized-case vaccination percentage for the season in the provided sources [2] [4]. Readers should expect variation by age, region, and season—and note that available sources do not mention a definitive U.S. national percentage of vaccinated hospitalized flu patients for 2024–25 (not found in current reporting).