RSV Vaccine Protection in Older Adults Persisted Across Several Winters but Gradually Faded

CATEGORY: IMMUNE HEALTH

One dose of an RSV vaccine cut cases of RSV-related chest illness in adults 60 and older by 62.9% across three full RSV seasons. The shield weakened winter by winter: 82.6% protection in the first season, 56.1% in the second, 48.0% in the third. Nearly 25,000 people took part in the randomized, placebo-controlled trial, published in The Lancet Respiratory Medicine.¹ A second dose, given a year after the first, was tested as well. It added no clear benefit.

Twenty-Five Thousand Adults, Watched for Three Winters

RSV, or respiratory syncytial virus, is a common winter virus that most people shrug off as a cold. In older adults it can descend into the lungs and turn dangerous. The trial behind these numbers was international and funded by the vaccine’s maker, GSK. A random allocation gave 12,468 adults the RSVPreF3 vaccine and 12,498 a placebo, and neither the participants nor the staff judging their illnesses knew who had received which. For a median of about two and a half years, every case of RSV-related lower respiratory tract disease was laboratory-confirmed and logged, season by season. That phrase covers illness reaching the airways of the chest, with symptoms like new wheezing, deep cough or shortness of breath.

From Four-Fifths Protection to About Half

The seasonal pattern was consistent. Strong protection at first, then a gradual slide. Across all three seasons combined, one dose prevented 62.9% of RSV chest illness and 51.1% of RSV respiratory illness of any severity. Protection behaved less like a switch that flips off than like a phone battery aging: by the third winter it no longer held its original charge, but it still carried enough to matter. Serious side effects judged related to vaccination were rare, occurring in fewer than 1% of participants.¹

The Second Dose That Added Little

The researchers built the revaccination question into the trial itself. Before the second season, part of the vaccinated group received another dose, to see whether an annual top-up would restore the first winter’s peak protection. It did not clearly do so. Across three seasons, protection in the revaccinated group came to 67.8%, in the same general range as a single dose. That unfulfilled expectation matches how the shot is handled in the United States, where the RSV vaccine is given as a one-time dose rather than repeated each year. Nor is durability unique to this product. In its own randomized trial, a competing RSV vaccine made by a different manufacturer also kept a substantial share of its protection through a second season without another dose.²

Key Takeaways

• One dose prevented 62.9% of RSV-related chest illness across three seasons in adults 60 and older, running from 82.6% in the first winter down to 48.0% by the third.
• A second dose a year later did not clearly improve on single-dose protection, which matches current U.S. practice of giving the vaccine once rather than annually.
• A separate randomized trial of a competing vaccine also found protection carrying into a second season, so multi-winter durability looks like a feature of the class rather than one product.
• Serious side effects judged related to the vaccine were rare, at fewer than 1% of participants.

References

1. Ison MG, 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
2. Walsh EE, Pérez Marc G, Falsey AR, et al. RENOIR Trial—RSVpreF Vaccine Efficacy over Two Seasons. The New England Journal of Medicine. 2024;391(15):1459–1460. link