Optimal COVID-19 vaccine prioritization by age depends critically on inter-group contacts and vaccination rates

TL;DR

This study analyzes how inter-group contacts and vaccination rates influence optimal COVID-19 vaccination strategies, highlighting the critical role of social contact reductions in improving outcomes and informing tailored interventions.

Contribution

It provides a comprehensive analysis of 362,880 vaccination scenarios considering contact patterns and reinfection, revealing the importance of social contact reductions in strategy effectiveness.

Findings

Optimal strategies vary with vaccination rates and contact restrictions.

Contact reductions significantly improve vaccination outcomes.

Moderate vaccination rates combined with social restrictions can halt infection spread.

Abstract

The limited availability of COVID-19 vaccines has prompted extensive research on optimal vaccination strategies. Previous studies have considered various non-pharmaceutical interventions, vaccine efficacy, and distribution strategies. In this work, we address the combined effects of inter-group contacts and vaccination rates under contact reduction, analyzing the Spanish population's demographic and age group contact patterns and incorporating reinfection dynamics. We conduct an exhaustive analysis, evaluating 362,880 permutations of 9 age groups across 6 vaccination rates and two distinct, empirically quantified scenarios for social contacts. Our results show that at intermediate-to-high vaccination rates with unrestricted social contacts, optimal age-based vaccination strategies only slightly deviate from older-to-younger prioritization, yielding marginal reductions in deaths and infections. However, when significant reductions in social contacts are enforced -similar to the lockdowns in 2020-, there are substantial improvements, particularly at moderate vaccination rates. These restrictions lead to a transition where infection propagation is halted, a scenario that became achievable during the pandemic with the observed vaccination rates. Our findings emphasize the importance of combining appropriate social contact reductions with vaccination to optimize age-based vaccination strategies, underscoring the complex, nonlinear dynamics involved in pandemic dynamics and the necessity for tailored, context-specific interventions.