An RSV vaccine cut hospital stays in older adults, with most to gain for weak immunity
Infections and vaccines after 50Part of a story we are following · 9 articles · See every update
The RSV vaccine’s overall effectiveness against hospitalization was 83.3% in older adults in Denmark, and unvaccinated people with weakened immunity were hospitalized more than nine-fold as often, in an analysis of the DAN-RSV trial published in October 2026 in The Lancet Healthy Longevity. People with weak immunity may gain most from protection against these infections.
RSV, or respiratory syncytial virus, can cause serious lung infections in older adults, and people with weakened immune systems are at even higher risk. The DAN-RSV trial in Denmark randomly offered more than a hundred thousand older adults an RSV vaccine.
What did the trial test?
In November and December 2024, 131 276 adults aged 60 or older in Denmark were randomly assigned to a single dose of a bivalent RSV prefusion F vaccine, RSVpreF, or no vaccine. Among them, 5199, or 4.0%, had immunosuppression, defined as at least one hospital encounter for an immune-weakening condition or treatment. Hospitalizations were tracked through national registries until May 31, 2025.
What did the study find about infections?
| Result | |
|---|---|
| RSV hospitalization without vaccine, weakened immunity | 4.68 per 1000 person-years |
| RSV hospitalization without vaccine, normal immunity | 0.50 per 1000 person-years |
| Vaccine effectiveness, overall | 83.3% |
| Vaccine effectiveness, weakened immunity | 60.5% (very uncertain) |
| Vaccine effectiveness, normal immunity | 92.3% |
The difference in effectiveness between groups was not statistically significant, and only 21 people in total were hospitalized with RSV, so the estimate for people with weakened immunity was very imprecise.
Why does this matter?
People with weakened immunity were far more likely to land in the hospital with RSV. Even if the vaccine works somewhat less well in them, the absolute benefit could be larger because their risk is so much higher. The authors suggest prioritizing vaccination in this group.
How solid is this evidence?
It’s good. Mongevity rates it B on our A-to-E scale: a large randomized trial, but this is a subgroup analysis that wasn’t powered to detect differences, the trial was open-label, it covered one season and it was funded by the vaccine maker.
What are the open questions?
Larger studies are needed to confirm how well the vaccine protects people with different types of immunosuppression, such as cancer treatment, transplants or immune-suppressing drugs, and whether a second dose helps.
What does this mean for you?
If you’re 60 or older, and especially if you have a condition or take medicines that weaken your immune system, ask your doctor whether an RSV vaccine is recommended for you this season.
How do I explain this at dinner?
In a huge Danish trial, an RSV vaccine kept many older adults out of the hospital. People with weak immune systems were more than nine times as likely to be hospitalized without it, so they may benefit most. A good question for the table: who in your family is at higher risk from winter viruses?
In one sentence: an RSV vaccine reduced RSV hospitalizations in adults 60 and older, and people with weakened immunity, whose risk was far higher, could gain the most.
Questions and answers
- Who is at highest risk from RSV?
- Older adults with weakened immunity: unvaccinated, their RSV hospitalization rate was 4.68 vs. 0.50 per 1000 person-years.
- How well did the vaccine work?
- Overall effectiveness against RSV hospitalization was 83.3%.
- Does it work with weakened immunity?
- The estimate was 60.5%, but very uncertain; there was no statistical evidence that it differed from other people.
