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

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 extended 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 identified optimal vaccine allocation strategies within- and between-countries to maximise averted deaths under constraints on dose supply. We found 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.

Vaccines and variants: Modelling insights into emerging issues in COVID-19 epidemiology

“…Given low vaccine efficacy, low coverage, or sustained transmission, prioritizing individuals >60 years of age should lead to the greatest reductions in hospitalisations and mortality (37) , while targeting younger individuals should lead to the greatest reduction in incidence (14) . However, clear thresholds for vaccine efficacy and population-level coverage were identified, beyond which (e.g., when vaccine supply increases) a suppression strategy that targets middle-aged (30–59) transmitters becomes optimal across all optimisation targets (e.g., incidence, hospitalisations, and deaths) [13] , [38] . Because human contact patterns are heterogeneous but broadly understood, targeted strategies are likely to be far more effective at reducing disease burden than indiscriminate vaccination campaigns, whether targeting is directed according to age (14) , occupation (e.g.…”

“…essential-workers; 29), or those with higher degrees of social connectivity (40) . Similarly, at the global level, several modelling studies have found that allocating available doses in proportion to each country’s population size (compared to the current practices favouring high-income countries) is close to the optimal strategy (13) and could double the global number of deaths averted (41) . Further, initially distributing single doses (for two dose vaccines) should avert more deaths than providing fewer people with two doses, provided that protection conferred by a single dose is sufficiently high [12] , [42] .…”

“…For example, models have explicitly captured social interactions to project the consequences of reopening schools [4] , [5] , [6] , [7] , increasing the proportion of onsite workers [5] , [8] , and reinstating international travel [9] , [10] . Analyses are now shifting to focus on understanding characteristics of mutating viruses (11) and optimising vaccine distribution [12] , [13] , [14] . Here, we update previous insights on the role of models in understanding COVID-19 epidemiology (15) with respect to vaccination and VoC.…”

Rural prioritization may increase the impact of COVID-19 vaccines in Sub-Saharan Africa due to ongoing internal migration: A modeling study

“…The copyright holder for this preprint this version posted June 21, 2021. ; https://doi.org/10.1101/2021.06. 18.21259164 doi: medRxiv preprint cination would yield the largest reductions in mortality [3,4] given the steep gradient of mortality observed with age in China, Europe, and other countries [5,6]. Meanwhile, HCW have been prioritized to preserve health system capacity [2].…”

Mathematical modeling of vaccination rollout and NPIs lifting on COVID-19 transmission with VOC: a case study in Toronto, Canada

“…There have been numerous mathematical models aiming to identify the best vaccination strategy 7,8,9,10,11,12,13,14,15,16 . Early models focused on reducing the spread of the infection and identifying priority groups for receiving the first dose.…”