When to Boost: How Dose Timing Determines the Epidemic Threshold

TL;DR

This paper analyzes how the timing and prioritization of vaccine doses influence the epidemic threshold, providing strategies to optimize vaccination schedules for disease eradication.

Contribution

It introduces a theoretical framework and validation methods to determine optimal dose scheduling and prioritization based on vaccination rates.

Findings

Prioritizing first doses at low vaccination rates prevents outbreaks.

High vaccination rates benefit from scheduling that outperforms first-come-first-served.

Adjusting inter-dose timing significantly impacts epidemic outcomes.

Abstract

Most vaccines require multiple doses, the first to induce recognition and antibody production and subsequent doses to boost the primary response and achieve optimal protection. We show that properly prioritizing the administration of first and second doses can shift the epidemic threshold, separating the disease-free from the endemic state and potentially preventing widespread outbreaks. Assuming homogeneous mixing, we prove that at a low vaccination rate, the best strategy is to give absolute priority to first doses. In contrast, for high vaccination rates, we propose a scheduling that outperforms a first-come first-served approach. We identify the threshold that separates these two scenarios and derive the optimal prioritization scheme and inter-dose interval. Agent-based simulations on real and synthetic contact networks validate our findings. We provide specific guidelines for effective resource allocation, showing that adjusting the timing between primer and booster significantly impacts epidemic outcomes and can determine whether the disease persists or disappears.