In Older Adults, Flu Vaccination Went With Modestly Fewer Hospitalizations

CATEGORY: DISEASE PREVENTION

Among adults aged 65 and older, having a flu shot before the season tracked with about 14% fewer hospitalizations for influenza, in a Taiwanese study of more than two million people. In plain counts that is roughly 3.1 hospital stays per 1,000 people a year against 3.7. Influenza is a contagious respiratory infection. The comparison sets people who took the shot beside people who did not, so it describes a link.¹

Why Influenza Turns Serious Later in Life

An aging immune system answers an infection more slowly. That lag gives influenza room to become something worse: a hospital stay, or pneumonia, an infection that fills the lungs’ air sacs with fluid. So the useful question is not simply whether vaccination prevents infections. It is whether vaccination changes the outcomes that put people in a hospital bed.

A Trial Built Out of Insurance Records

Nobody can randomly assign flu shots to two million people. So the researchers built the closest available substitute from Taiwan’s national health-insurance records, an approach called target trial emulation. From the 2018-2019 season they matched 1.2 million vaccinated adults aged 65 and older to 1.2 million unvaccinated adults who resembled them, then followed hospital records through the season and beyond it.¹ Matching is not randomization. People who get vaccinated differ from people who do not in ways that records cannot fully capture, which keeps this observational, and the extra checks the authors ran were aimed at narrowing that gap.

Forty-Seven Vaccinations, One Hospital Stay Averted

The authors translated the 14% into a second form: about 47 people would need to be vaccinated for one season to prevent a single influenza hospitalization.¹ Among those admitted anyway, vaccination went with milder courses, including about 30% lower risk of influenza-related death and about 12% lower risk of pneumonia. Protection ran strongest early in the season and among adults aged 65 to 74. One result broke from the rest. Vaccination showed no significant link with fewer influenza-related outpatient or emergency room visits, even while the gap in hospital admissions held.¹

Enhanced Shots Added 11% to 18%

A single season in a single country cannot stand in for every year or every population, since flu strains shift and so does the match between strain and vaccine. Wider evidence fills that in. A 2025 meta-analysis, which pools results from many earlier studies, covering nearly 193,000 people tied vaccination to less severe illness and fewer deaths at every age, though protection against catching the H3N2 strain was weaker in older adults.² A separate review of adults 65 and older tied enhanced formulations, designed to provoke a stronger immune response, to about 11% to 18% fewer flu hospitalizations than standard-dose shots.³

Key Takeaways

• Among more than two million adults aged 65 and older, flu vaccination was associated with about 14% fewer influenza hospitalizations, or roughly 3.1 stays per 1,000 people a year against 3.7.
• Among people admitted anyway, vaccination was associated with fewer serious complications, including pneumonia and influenza-related death. No clear link showed up with fewer outpatient or emergency room visits.
• Records were matched, not randomized. The study points to an association rather than showing the vaccine produced these outcomes.

References

1. Peng ZY, Hua YT, Huang WT, Wu JS, Ou HT. Reduced risks of influenza-associated hospitalization and complications following vaccination among over 2 million older individuals: a nationwide study using target trial emulation framework. BMC Medicine. 2025;23:157. link
2. Presa J, Arranz-Herrero J, Alvarez-Losa L, et al. Influenza vaccine outcomes: a meta-analysis revealing morbidity benefits amid low infection prevention. European Respiratory Review. 2025;34(175):240144. link.
3. Ferdinands JM, Blanton LH, Alyanak E, et al. Protection against influenza hospitalizations from enhanced influenza vaccines among older adults: a systematic review and network meta-analysis. Journal of the American Geriatrics Society. 2024;72(12):3875–3889. link.