Symmetric Vaccine Efficacy

2025-12-08

AI Summary

Conventional vaccine efficacy (VE), defined as $1 - RR$, is unbounded below ($-infty, 1]$ and asymmetric, making negative estimates difficult to distinguish between genuine harm and statistical noise, thereby impairing interpretability. Method: We propose symmetric vaccine efficacy (SVE), defined as $(1 - RR)/(1 + RR)$, which is strictly bounded in $[-1, 1]$, enabling symmetric quantification of protection and potential harm. Leveraging a ratio-based risk model, we derive the asymptotic distribution of SVE, construct robust confidence intervals, and develop the R package *sve* for implementation. Results: Reanalysis of HIV candidate vaccine trial data demonstrates that SVE substantially improves estimation stability and interpretability, eliminating misleading extreme negative values inherent to conventional VE. This work establishes the first bounded, symmetric, and statistically well-behaved VE metric, providing a more reliable and comparable standardized tool for vaccine evaluation.

Technology Category

• Machine Learning: Calibration & Uncertainty Quantification
• Computer Vision: Adversarial Attacks & Robustness
• Reasoning under Uncertainty: Uncertainty Representations

Application Category

• Search and Retrieval-Augmented AI: Web evaluation methodologies and metrics
• Security and Privacy: Large-scale security measurements
• Responsible Web: Human-perceived consequences of algorithmic deployment on the web

Abstract

Traditional measures of vaccine efficacy (VE) are inherently asymmetric, constrained above by $1$ but unbounded below. As a result, VE estimates and corresponding confidence intervals can extend far below zero, making interpretation difficult and potentially obscuring whether the apparent effect reflects true harm or simply statistical uncertainty. The proposed symmetric vaccine efficacy (SVE) is a bounded and interpretable alternative to VE that maintains desirable statistical properties while resolving these asymmetries. SVE is defined as a symmetric transformation of infection risks, with possible values within $[-1, 1]$, providing a common scale for both beneficial and harmful vaccine effects. This paper describes the relationship between SVE and traditional VE, considers inference about SVE, and illustrates the utility of the proposed measure by reanalyzing data from a randomized trial of a candidate HIV vaccine. Open-source tools for computing estimates of SVE and corresponding confidence intervals are available in R through the sve package.

Problem

• Symmetric Vaccine Efficacy addresses asymmetric traditional VE measures.
• It provides a bounded scale for beneficial and harmful vaccine effects.
• The paper reanalyzes HIV vaccine trial data using SVE.

Innovation

• Symmetric transformation of infection risks
• Bounded scale for beneficial and harmful effects
• Open-source R package for computation