Number Needed to Treat (NNT) for RSV Vaccination in Geriatric Patients
The NNT to prevent one RSV-associated hospitalization over two RSV seasons ranges from approximately 159-233 for adults ≥75 years, 158-395 for adults 60-74 years with chronic conditions, and 1,370-2,463 for adults 60-74 years without chronic conditions, depending on the vaccine product used. 1
Calculating NNT from Available Data
The most direct NNT calculations come from the 2024 ACIP recommendations, which provide preventable outcomes per 1 million doses administered over two consecutive RSV seasons:
GSK Arexvy (RSVPreF3)
- Adults ≥75 years: 4,283 hospitalizations prevented per 1 million doses = NNT of 233 1
- Adults 60-74 years with ≥1 chronic condition: 2,839 hospitalizations prevented per 1 million doses = NNT of 352 1
- Adults 60-74 years without chronic conditions: 456 hospitalizations prevented per 1 million doses = NNT of 2,193 1
Pfizer Abrysvo (RSVpreF)
- Adults ≥75 years: 3,817 hospitalizations prevented per 1 million doses = NNT of 262 1
- Adults 60-74 years with ≥1 chronic condition: 2,530 hospitalizations prevented per 1 million doses = NNT of 395 1
- Adults 60-74 years without chronic conditions: 406 hospitalizations prevented per 1 million doses = NNT of 2,463 1
NNT for Severe Disease and Mortality
The benefit-risk analysis also provides data on preventing ICU admissions and deaths, though these are combined outcomes in the ACIP tables:
- For adults ≥75 years: The combined ICU admissions and deaths prevented range from 561-630 per million doses for Abrysvo and 605-630 per million doses for Arexvy, translating to an NNT of approximately 1,587-1,783 to prevent one ICU admission or death 1
Real-World Effectiveness Data Supporting NNT Calculations
Recent real-world effectiveness studies validate these NNT estimates:
A 2025 Danish pragmatic trial demonstrated that among 131,276 participants ≥60 years, RSVpreF prevented hospitalization for RSV-related respiratory tract disease with vaccine effectiveness of 83.3%, with only 3 hospitalizations in the vaccinated group versus 18 in controls 2
Real-world US data from 2023-2024 showed vaccine effectiveness of 75.1% against RSV-associated acute respiratory infection, with effectiveness of 75-82% against RSV-associated hospitalization across age groups 3, 4
Important Clinical Context for Interpreting NNT
Age-Stratified Risk Matters Significantly
The NNT varies dramatically by age because baseline risk increases substantially with advancing age:
- Adults ≥75 years have RSV-associated hospitalization rates of 210-343 per 100,000 annually, compared to lower rates in younger age groups 1
- The NNT is 6-10 times lower (more favorable) in adults ≥75 years compared to healthy adults 60-74 years 1
Comorbidity Status Dramatically Affects NNT
Adults 60-74 years with chronic conditions have an NNT approximately 6-7 times more favorable than those without chronic conditions 1. High-risk conditions include:
- COPD, asthma, chronic heart failure, diabetes, chronic kidney disease, and severe obesity (BMI ≥40) 1
- Immunocompromised states, including transplant recipients and those on immunosuppressive therapy 5
NNT Over Multiple Seasons
The NNT calculations above reflect outcomes over two consecutive RSV seasons, as vaccine efficacy wanes over time:
- First season efficacy: 82.6% (Arexvy) and 65.1-88.9% (Abrysvo) 1
- Second season efficacy: 56.1% (Arexvy) and 55.7% (Abrysvo) 1
- Third season efficacy: 48.0% (Arexvy) 1
Number Needed to Harm (NNH) for Context
To provide complete benefit-risk context, the NNH for Guillain-Barré syndrome is:
- RSVPreF3 (Arexvy): 333 doses per GBS case (3 cases per million doses) 1
- RSVpreF (Abrysvo): 62,500 doses per GBS case (16 cases per million doses) 1
The number of hospitalizations, ICU admissions, and deaths prevented exceeded the estimated vaccine-attributable GBS cases across all age and risk groups 1, 4
Practical Application Algorithm
For adults ≥75 years: Universal vaccination is recommended with highly favorable NNT of 159-233 to prevent one hospitalization 1, 5
For adults 60-74 years with chronic conditions: Vaccination is recommended with favorable NNT of 158-395 to prevent one hospitalization 1, 5
For adults 60-74 years without chronic conditions: Vaccination may be considered, but NNT is substantially higher at 1,370-2,463 to prevent one hospitalization 1