Within-country age-based prioritisation, global allocation, and public health impact of a vaccine against SARS-CoV-2: A mathematical modelling analysis

Alexandra B Hogan,Robert Verity,Edward Knock,Nicholas F Brazeau,Daniel J Laydon,Farzana Muhib,Peter Winskill,Katharina Hauck,John A Lees,Alessandra Løchen,Marc Baguelin,Arran Hamlet,Charles Whittaker,Katy A M Gaythorpe ,Neil Ferguson ,Giovanni Charles ,Lilith K Whittles ,Oliver Watson ,Patrick Walker ,Azra C Ghani

doi:10.1016/j.vaccine.2021.04.002

Abstract

The worldwide endeavour to develop safe and effective COVID-19 vaccines has been extraordinary, and vaccination is now underway in many countries. However, the doses available in 2021 are likely to be limited. We extend a mathematical model of SARS-CoV-2 transmission across different country settings to evaluate the public health impact of potential vaccines using WHO-developed target product profiles. We identify optimal vaccine allocation strategies within- and between-countries to maximise averted deaths under constraints on dose supply. We find that the health impact of SARS-CoV-2 vaccination depends on the cumulative population-level infection incidence when vaccination begins, the duration of natural immunity, the trajectory of the epidemic prior to vaccination, and the level of healthcare available to effectively treat those with disease. Within a country we find that for a limited supply (doses for < 20% of the population) the optimal strategy is to target the elderly. However, with a larger supply, if vaccination can occur while other interventions are maintained, the optimal strategy switches to targeting key transmitters to indirectly protect the vulnerable. As supply increases, vaccines that reduce or block infection have a greater impact than those that prevent disease alone due to the indirect protection provided to high-risk groups. Given a 2 billion global dose supply in 2021, we find that a strategy in which doses are allocated to countries proportional to population size is close to optimal in averting deaths and aligns with the ethical principles agreed in pandemic preparedness planning.

Highlights

COVID-19 has caused an unprecedented global public health and economic challenge which will continue to disrupt lives and livelihoods until a preventative intervention, such as a vaccine, becomes widely available
We extend a model of SARS-CoV-2 transmission to explore the public health impact of different vaccine characteristics, epidemic stages, and population-targeting strategies
We explore the implications of these characteristics for within-country allocation and global allocation and quantify the maximum public health benefit of different allocation strategies under a range of likely supply constraints, over the time periods 2021 only and 2021–2022

Summary

Introduction

COVID-19 has caused an unprecedented global public health and economic challenge which will continue to disrupt lives and livelihoods until a preventative intervention, such as a vaccine, becomes widely available. Even as some countries begin to introduce approved vaccines, the demand for doses is likely to exceed supply through 2021 due to constraints in manufacturing. To meet principle B, vaccine dose allocation will need to be balanced against both life-expectancy (in order to minimise life-years lost) and the additional variation in the risk of death resulting from, for example, inequitable access to healthcare across the globe. Aligned with principle D, it is likely that any vaccine allocation would prioritise essential workers such as those providing the frontline health response[14]. Adhering to these principles to derive a fair and optimal allocation strategy, given limited vaccine stocks is far from straightforward

Methods

Results

Conclusion