Estimating Vaccine Efficacy Against Transmission via Effect on Viral Load.

Lee Kennedy-Shaffer,Marc Lipsitch,Rebecca Kahn

doi:10.1097/ede.0000000000001415

Lee Kennedy-Shaffer, Marc Lipsitch + Show 1 more

Open Access

https://doi.org/10.1097/ede.0000000000001415

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Abstract

Determining policies to end the SARS-CoV-2 pandemic will require an understanding of the efficacy and effectiveness (hereafter, efficacy) of vaccines. Beyond the efficacy against severe disease and symptomatic and asymptomatic infection, understanding vaccine efficacy against virus transmission, including efficacy against transmission of different viral variants, will help model epidemic trajectory and determine appropriate control measures. Recent studies have proposed using random virologic testing in individual randomized controlled trials to improve estimation of vaccine efficacy against infection. We propose to further use the viral load measures from these tests to estimate efficacy against transmission. This estimation requires a model of the relationship between viral load and transmissibility and assumptions about the vaccine effect on transmission and the progress of the epidemic. We describe these key assumptions, potential violations of them, and solutions that can be implemented to mitigate these violations. Assessing these assumptions and implementing this random sampling, with viral load measures, will enable better estimation of the crucial measure of vaccine efficacy against transmission.

Highlights

Determining policies to end the SARS-CoV-2 pandemic will require an understanding of the efficacy and effectiveness of vaccines
Similar methods have been proposed to estimate the vaccine efficacy on incident infection, accounting for vaccine effects that change the duration of infection by incorporating random sampling and testing among randomized controlled trials (RCTs) participants.[17,18]
Follmann and Fay focus on the inferential method and statistical properties of such an estimator,[18] we focus here on assumptions about the infection and transmission process and the vaccine effect that are necessary for consistent estimation of this effect and for proper interpretation of observed differences in viral load

Summary

Introduction

Determining policies to end the SARS-CoV-2 pandemic will require an understanding of the efficacy and effectiveness (hereafter, efficacy) of vaccines. Under the assumptions that: the incidence rate in each arm of the trial is constant across time (Assumption 1); and vaccination status does not affect the probability of having contact with a susceptible individual given that an individual is infectious (Assumption 2), the vaccine efficacy against transmission is given by: VET

Results

Conclusion