RSV Vaccine Cuts Hospitalizations 83% in Older Adults — Even the Immunosuppressed
A large Danish RCT finds Pfizer's RSVpreF vaccine dramatically reduces RSV hospitalizations in adults 60+, with high-risk immunosuppressed patients showing the greatest absolute benefit.
Summary
A nationwide Danish randomized trial of over 131,000 adults aged 60 and older tested the bivalent RSV prefusion F protein vaccine (RSVpreF) against no vaccination. Overall, the vaccine reduced RSV-related hospitalizations by 83%. Among the 4% of participants who were immunosuppressed — a group with more than nine times the baseline RSV hospitalization rate of non-immunosuppressed individuals — the vaccine showed a numerically lower but statistically similar effect. The absolute risk reduction was largest in immunosuppressed adults, suggesting they stand to gain the most from vaccination. The study could not statistically confirm a difference in vaccine effectiveness between subgroups due to limited event numbers. Results support prioritizing RSV vaccination in immunosuppressed older adults pending larger confirmatory studies.
Detailed Summary
Respiratory syncytial virus (RSV) is a serious and underappreciated threat to older adults, causing substantial hospitalizations and mortality in people over 60. Those with immunosuppression — due to cancer treatment, organ transplant, or immune-modulating therapies — face even steeper risks. This prespecified analysis of the DAN-RSV trial examined whether Pfizer's bivalent RSVpreF vaccine performs equivalently in immunosuppressed versus immunocompetent older adults.
The DAN-RSV trial was a pragmatic, open-label, nationwide randomized clinical trial conducted across Denmark from November to December 2024. Over 131,000 adults aged 60 and older were randomized 1:1 to receive a single dose of RSVpreF or no vaccine. Immunosuppression was defined as at least one hospital encounter involving an immunosuppressive condition or treatment. Outcome data were drawn from nationwide registries, with follow-up extending through May 2025.
The headline result confirmed the vaccine's strong overall effectiveness: RSVpreF reduced RSV-related respiratory hospitalizations by 83.3% (95% CI: 42.9–96.9%) across the full population. Among the 5,199 immunosuppressed participants, the incidence of RSV hospitalization in unvaccinated individuals was more than nine times higher than in non-immunosuppressed controls (4.68 vs. 0.50 events per 1,000 person-years). Vaccine effectiveness in the immunosuppressed subgroup was 60.5%, compared to 92.3% in those without immunosuppression, but the interaction p-value was 0.22 — no statistically significant difference between groups.
Critically, the estimated absolute rate reduction was largest among immunosuppressed adults (2.83 fewer hospitalizations per 1,000 person-years vs. 0.46 in non-immunosuppressed adults), meaning that even if relative effectiveness is modestly lower, the absolute benefit of vaccination is substantially greater in this high-risk group.
Limitations include underpowering for subgroup analysis — only 21 total RSV hospitalization events occurred, seven of which were in immunosuppressed participants — making definitive conclusions impossible. The summary is based on the abstract only, and Pfizer funded the trial.
Key Findings
- RSVpreF vaccine reduced RSV hospitalizations by 83% overall in adults aged 60+ in a large Danish RCT.
- Immunosuppressed adults had 9x higher baseline RSV hospitalization rates than non-immunosuppressed peers.
- Vaccine effectiveness was 60.5% in immunosuppressed vs. 92.3% in non-immunosuppressed adults, but the difference was not statistically significant.
- Absolute risk reduction was ~6x greater in immunosuppressed adults, supporting prioritized vaccination in this group.
- No statistically significant interaction between immunosuppression status and vaccine effectiveness was detected (p=0.22).
Methodology
Prespecified subgroup analysis of a pragmatic, open-label, nationwide randomized clinical trial in Denmark (DAN-RSV); 131,276 adults aged 60+ randomized 1:1 to RSVpreF or no vaccine during November–December 2024. Outcomes ascertained via nationwide health registries with follow-up through May 2025.
Study Limitations
The subgroup analysis was underpowered — only 7 RSV hospitalization events occurred in immunosuppressed vaccinated vs. unvaccinated participants combined — making the 60.5% effectiveness estimate highly uncertain with a confidence interval crossing zero. The trial was Pfizer-funded, introducing potential conflicts of interest. This summary is based on the abstract only, as the full text is not open access.
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