In Older Adults, Flu Vaccination Went With Modestly Fewer Hospitalizations

CATEGORY: DISEASE PREVENTION

A yearly flu shot may do more than spare you a few days of fever and aches. In a Taiwanese study of more than two million adults aged 65 and older, those who were vaccinated before flu season were about 14% less likely to be hospitalized for influenza—a contagious respiratory infection—than those who went unvaccinated.¹

Slower Immune Response Makes Flu More Serious

As you age, your immune system responds more slowly to infections, so influenza is more likely to turn serious. In older adults, the flu can lead to hospital stays and dangerous complications such as pneumonia—an infection that fills the lungs’ air sacs with fluid. That is why researchers have focused on whether vaccination lowers not just infections, but the severe outcomes that land people in the hospital.

1.2 Million Vaccinated Matched to Similar Unvaccinated Adults

Researchers used Taiwan’s national health-insurance records to mimic a clinical trial without assigning shots themselves—an approach called target trial emulation. From the 2018–2019 flu season, they carefully matched 1.2 million vaccinated adults with 1.2 million similar unvaccinated adults aged 65 and older, then tracked hospital records across the season and beyond.¹ Because no one was randomly assigned, this is an observational study that shows an association, not proof of cause and effect; the matching and additional checks were designed to make the comparison as fair as possible.

About 3.1 Versus 3.7 Hospital Stays per 1,000

Vaccinated older adults had roughly 14% lower risk of being hospitalized for influenza—about 3.1 versus 3.7 hospital stays for every 1,000 people each year. The authors reported that about 47 people would need to be vaccinated for one season to avert one influenza-related hospitalization.¹ Among those who were hospitalized, vaccination was also linked to fewer serious complications, including about 30% lower risk of influenza-related death and about 12% lower risk of pneumonia. Protection tended to be strongest earlier in the season and among adults aged 65 to 74. Vaccination showed no significant link with fewer influenza-related outpatient or emergency room visits, unlike the clearer reduction in hospital admissions.¹

Two Million People, One Season, One Country

The size of this study—more than two million people—and its careful design make the link between flu vaccination and fewer severe outcomes hard to ignore, even though a single season in one country cannot capture every year or population. The findings add to a large body of evidence that seasonal vaccination is associated with fewer flu-related hospital stays in older adults.

Enhanced Formulations Linked to 11% to 18% Fewer Hospitalizations

A 2025 meta-analysis, a study pooling results from many earlier ones, covering nearly 193,000 people linked vaccination to less severe illness and fewer deaths at every age, though protection against catching the H3N2 strain of flu was weaker in older adults.² A separate review of adults 65 and older linked enhanced vaccine formulations, designed to produce a stronger immune response, to about 11% to 18% fewer flu hospitalizations than standard-dose shots.³

Key Takeaways

• In over two million adults aged 65 and older, flu vaccination was linked to about 14% lower risk of being hospitalized for influenza.
• Among those hospitalized, vaccination was associated with fewer serious complications, including pneumonia and influenza-related death.
• This is an observational study, so it shows an association rather than proof that the vaccine directly prevents 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.