Symmetric vaccine efficacy

Area of Science:

• Biostatistics
• Vaccinology
• Epidemiology

Background:

• Traditional vaccine efficacy (VE) measures are asymmetric, bounded above by 1 but not below.
• This asymmetry can lead to difficulties in interpreting VE estimates and confidence intervals (CIs), potentially obscuring true vaccine effects or indicating statistical uncertainty.

Purpose of the Study:

• To introduce and define symmetric vaccine efficacy (SVE) as a bounded and interpretable alternative to traditional VE.
• To explore the statistical properties and inferential methods for SVE.
• To demonstrate the utility of SVE using real-world vaccine trial data.

Main Methods:

• Defined SVE as a symmetric transformation of infection risks, yielding values between -1 and 1.
• Analyzed the relationship between SVE and traditional VE.
• Developed methods for statistical inference regarding SVE.
• Reanalyzed data from a candidate HIV vaccine trial using SVE.

Main Results:

• SVE provides a bounded scale [-1, 1] for vaccine effects, accommodating both benefits and harms.
• The proposed SVE measure resolves the asymmetries inherent in traditional VE.
• Application to HIV vaccine trial data illustrated the practical utility of SVE.

Conclusions:

• SVE is a statistically sound and interpretable measure for vaccine efficacy, offering advantages over traditional VE.
• SVE facilitates a clearer understanding of vaccine performance, including potential adverse effects.
• Open-source R tools are available for computing SVE estimates and CIs.