The Number Needed to Immunize (NNI) to Assess the Benefit of a Prophylaxis Intervention with Monoclonal Antibodies Against RSV
Abstract
1. Introduction
2. Materials and Methods
2.1. Search Strategy
2.2. Study Selection
3. Results
3.1. Search Results
3.2. Definition and Context of Application of NNI
3.3. Calculating NNI
3.4. Summary of the Results of the Studies on NNI Applied to Monoclonal Antibodies Against RSV Disease
4. Discussion
4.1. Limitations of NNV and NNI
4.2. Advantages of NNV and NNI
4.3. Comparison of NNI with NNV of Some Vaccination Strategies
4.4. Use of Nirsevimab for RSV Prevention
4.5. The Practical Implications of Using NNI in Health Policy Decision-Making
4.6. Limitations of Study
5. Conclusions
Author Contributions
Funding
Conflicts of Interest
References
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NNT (Number Needed to Treat) | NNV (Number Needed to Vaccinate) | NNI (Number Needed to Immunize) | |
---|---|---|---|
Definition | The number of subjects needed to treat in order to prevent one outcome | The number of subjects needed to vaccinate in order to prevent one outcome | The number of subjects needed to be immunized to prevent one outcome |
Population | Patients | Healthy subjects | Healthy subjects |
Intervention | Medication | Vaccine | Vaccine or antibody |
Outcomes | Recovery | Active prevention | Active or passive prevention |
Authors | Journal | Year | Country | NNI Use | Context |
---|---|---|---|---|---|
Finelli et al. [35] | Vaccine | 2020 | USA | NNI to prevent one RSV-associated outpatient visit; NNI to prevent one RSV-associated lower respiratory tract infection (LRI) outpatient visit; RSV-associated hospitalizations | NNI to prevent RSV with extended half- life monoclonal antibody (EHL-mAb) |
Francisco et al. [36] | Anales de Pediatrìa (English edition) | 2023 | Spain | NNI to prevent one RSV-associated hospitalization; NNI to prevent one RSV-associated hospitalization combined with severe disease | Francisco et al., in a Statement of the Spanish Society of Paediatric Infectious Disease (SEIP), provided recommendations for the administration of nirsevimab for prevention of RSV disease |
O’Leary et al. [37] | Pediatrics | 2023 | USA | NNI with nirsevimab to prevent outpatient visits; NNI with nirsevimab to prevent emergency department visits; NNI with nirsevimab to prevent hospital admissions; NNI with nirsevimab to prevent Intensive Care Unit (ICU) admissions | The Advisory Committee on Immunization Practices (ACIP), a group of medical and public health experts that provides advice to the Centers for Disease Control and Prevention (CDC) |
Mallah et al. [19] | The Lancet Infectious Diseases | 2024 | Spain | NNI to avoid one RSV-related lower respiratory tract infection (LRTI) hospitalization | Results of a population-based longitudinal study |
Marcellusi et al. [39] | Global and Regional Health Technology Assessment | 2025 | Italy | NNI to prevent one RSV-related event per season | NNI is used to describe the potential benefits of a new prophylaxis strategy targeting all infants with nirsevimab compared to the current prophylaxis with palivizumab |
Outcome | AGE | Immunization Efficacy | NNI |
---|---|---|---|
RSV-associated outpatient visit | 0–5 months | 50% | 9–25 (95% CI 7–37) |
70% | 7–18 (95% CI 5–25) | ||
90% | 5–14 (95% CI 4–18) | ||
6–11 months | 50% | 8–22 (95% CI 6–33) | |
70% | 6–16 (95% CI 5–23) | ||
90% | 5–12 (95% CI 4–17) | ||
RSV-associated LRI outpatient visit | 0–5 months | 50% | 24–44 (95% CI 17–76) |
70% | 17–32 (95% CI 13–50) | ||
90% | 14–25 (95% CI 10–37) | ||
6–11 months | 50% | 18–47 (95% CI 13–84) | |
70% | 13–33 (95% CI 10–56) | ||
90% | 10–26 (95% CI 8–42) | ||
RSV-associated hospitalizations | 0–5 months | 50% | 52–118 (95% CI 39–138) |
70% | 37–85 (95% CI 30–96) | ||
90% | 29–66 (95% CI 24–74) | ||
6–11 months | 50% | 149–392 (95% CI 95–526) | |
70% | 107–280 (95% CI 73–360) | ||
90% | 83–218 (95% CI 60–270) |
Strengths of NNI/NNV | Limits of NNI/NNV |
---|---|
NNI and NNV enable comparison to estimate the effort required to generate a significant public health impact, assuming high uptake and high coverage among the target population | NNI and NNV do not consider the indirect effects of vaccination |
NNI and NNV are tools for estimating the cost associated with preventing a single disease event | Absence of defined threshold for interpretation of NNI and NNV |
NNI can help to show the value of immunization to different stakeholders and decision makers | Possible underestimation for diseases with low R0 |
NNI enables comparison of different health strategies (not only preventive) |
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Boccalini, S.; Gironi, V.; Buscemi, P.; Bonanni, P.; Muzii, B.; Parisi, S.; Borchiellini, M.; Bechini, A. The Number Needed to Immunize (NNI) to Assess the Benefit of a Prophylaxis Intervention with Monoclonal Antibodies Against RSV. Vaccines 2025, 13, 791. https://doi.org/10.3390/vaccines13080791
Boccalini S, Gironi V, Buscemi P, Bonanni P, Muzii B, Parisi S, Borchiellini M, Bechini A. The Number Needed to Immunize (NNI) to Assess the Benefit of a Prophylaxis Intervention with Monoclonal Antibodies Against RSV. Vaccines. 2025; 13(8):791. https://doi.org/10.3390/vaccines13080791
Chicago/Turabian StyleBoccalini, Sara, Veronica Gironi, Primo Buscemi, Paolo Bonanni, Barbara Muzii, Salvatore Parisi, Marta Borchiellini, and Angela Bechini. 2025. "The Number Needed to Immunize (NNI) to Assess the Benefit of a Prophylaxis Intervention with Monoclonal Antibodies Against RSV" Vaccines 13, no. 8: 791. https://doi.org/10.3390/vaccines13080791
APA StyleBoccalini, S., Gironi, V., Buscemi, P., Bonanni, P., Muzii, B., Parisi, S., Borchiellini, M., & Bechini, A. (2025). The Number Needed to Immunize (NNI) to Assess the Benefit of a Prophylaxis Intervention with Monoclonal Antibodies Against RSV. Vaccines, 13(8), 791. https://doi.org/10.3390/vaccines13080791