RSV Vaccination Prevented Hospital Stays in Older Adults

CATEGORY: IMMUNE HEALTH

Denmark ran a vaccine experiment the size of a small city last winter, and the unvaccinated half supplied nearly all the hospital cases. Among 131,276 adults aged 60 and older, half offered the RSV vaccine and half not, 18 unvaccinated participants were hospitalized with the virus over the season against 3 who’d been vaccinated, an 83% reduction.¹ It’s the first randomized evidence that the shot prevents the outcome it was built for: a hospital stay.

A National Registry Did the Counting

RSV, or respiratory syncytial virus, is a common winter lung virus. Most adults shrug it off as a cold. In older people it can descend into the lungs and become pneumonia-like illness, and until 2023 there was no vaccine against it. The earlier trials that won approval measured symptomatic illness in volunteers who kept symptom diaries.² Whether the vaccine keeps people out of the hospital had, until now, only been inferred from studies of people who chose vaccination on their own, a comparison always haunted by the possibility that the choosers were healthier to begin with. Here, a computer drew names from Denmark’s population registries. Those drawn got a digital invitation to be vaccinated free; the rest went about their winter as usual. Hospital diagnoses and lab tests, recorded nationally for everyone, settled the outcomes.

An 83% Drop in an Uncommon Event

The percentage is large; the everyday risk it shrinks is small. Even with no vaccine, RSV hospitalizations occurred at a rate of 0.66 per 1,000 participant-years, fewer than one per thousand people over a full year. The vaccine’s protection also reached beyond its named target. Hospital stays for severe lower-lung infections from RSV fell 92%, and admissions for respiratory illness of any cause dipped 15%, from 335 to 284, suggesting some RSV was hiding in cases nobody tested. Serious side effects were no more common in the vaccinated group. One winter and one country can’t say how long protection lasts, and a multi-season trial of a different RSV vaccine has already reported protection fading gradually over several years.³ But on the question that matters most for an older adult weighing the shot, the answer is no longer a guess.

Key Takeaways

• Randomly offering the RSV vaccine to half of 131,276 Danish adults 60 and older cut RSV hospitalizations 83% in one winter: 3 cases among the vaccinated versus 18 among the rest.
• The absolute risk was modest either way: even unvaccinated, RSV hospitalization struck fewer than one per thousand people per year.
• All-cause respiratory admissions fell 15%, and serious side effects didn’t differ between groups.
• Earlier evidence for preventing hospital stays came from people who chose vaccination themselves; this is the first test where a computer made the choice.

References

1. Lassen MCH, Johansen ND, Christensen SH, et al. RSV Prefusion F Vaccine for Prevention of Hospitalization in Older Adults. The New England Journal of Medicine. 2026;394(2):138–151. link
2. Walsh EE, Pérez Marc G, Falsey AR, et al. Efficacy and Safety of a Bivalent RSV Prefusion F Vaccine in Older Adults. The New England Journal of Medicine. 2023;388(16):1465–1477. link
3. Ison MG, Papi A, Athan E, et al. Efficacy, safety, and immunogenicity of the AS01E-adjuvanted respiratory syncytial virus prefusion F protein vaccine (RSVPreF3 OA) in older adults over three respiratory syncytial virus seasons (AReSVi-006): a multicentre, randomised, observer-blinded, placebo-controlled, phase 3 trial. The Lancet Respiratory Medicine. 2025;13(6):517–529. link