Optimising health and economic impacts of COVID-19 vaccine prioritisation strategies in the WHO European Region: a mathematical modelling study

Abstract

Background: Countries in the World Health Organization (WHO) European Region differ in terms of the COVID-19 vaccine supply conditions. We evaluated the health and economic impact of different age-based vaccine prioritisation strategies across this demographically and socio-economically diverse region.

Methods: We fitted age-specific compartmental models to the reported daily COVID-19 mortality in 2020 to inform the immunity level before vaccine roll-out. Models capture country-specific differences in population structures, contact patterns, epidemic history, life expectancy, and GDP per capita.We examined four strategies that prioritise: all adults (V+), younger (20-59 year-olds) followed by older adults (60+) (V20), older followed by younger adults (V60), and the oldest adults (75+) (V75) followed by incrementally younger age groups. We explored four roll-out scenarios (R1-4) - the slowest scenario (R1) reached 30% coverage by December 2022 and the fastest (R4) 80% by December 2021. Five decision-making metrics were summarised over 2021-22: mortality, morbidity, and losses in comorbidity-adjusted life expectancy, comorbidity- and quality-adjusted life years, and human capital. Six vaccine profiles were tested - the highest performing vaccine has 95% efficacy against both infection and disease, and the lowest 50% against diseases and 0% against infection.

Findings: Of the 20 decision-making metrics and roll-out scenario combinations, the same optimal strategy applied to all countries in only one combination; V60 was more or similarly desirable than V75 in 19 combinations. Of the 38 countries with fitted models, 11-37 countries had variable optimal strategies by decision-making metrics or roll-out scenarios. There are greater benefits in prioritising older adults when roll-out is slow and when vaccine profiles are less favourable.

Interpretation: The optimal age-based vaccine prioritisation strategies were sensitive to country characteristics, decision-making metrics, and roll-out speeds. A prioritisation strategy involving more age-based stages (V75) does not necessarily lead to better health and economic outcomes than targeting broad age groups (V60). Countries expecting a slow vaccine roll-out may particularly benefit from prioritising older adults.

Funding: World Health Organization, Bill and Melinda Gates Foundation, the Medical Research Council (United Kingdom), the National Institute of Health Research (United Kingdom), the European Commission, the Foreign, Commonwealth and Development Office (United Kingdom), Wellcome Trust.

Keywords: COVID-19; Europe; Health economics; Mathematical modelling; Multicountry analysis; Policy evaluation; Vaccine policy.

Fig. 1

Model Framework This figure describes the overall model framework of the study, which consists of the fitting and projection stages. The “known parameters based on existing knowledge” were used in both fitting and projection stages. The remaining input was used in only one of the stages as specified.

Fig. 2

Key inputs and assumptions. (A) Example population age structure (for the United Kingdom, unit = million; those of other countries in the Region are presented in Supplementary Figure 1). (B) Example age-specific within-population contact patterns (for the United Kingdom). (C) Vaccine roll-out scenarios and the respective proportions of populations expected to be covered at different time points. Note that under different vaccine roll-out scenarios, the starting time of vaccination programs may differ. Grey lines in the background represent observed country-level vaccine uptakes (of the first dose) over time reported in the WHO European Region (as of October 2021). (D) Vaccine prioritisation strategies. Hatched areas indicate when no vaccine was allocated. (E) Vaccine profiles consisting of vaccine efficacy against infection and disease.

Fig. 3

Results of the fitting stage (A-C) Comparisons between observed (blue line) and predicted COVID-19 deaths using a deterministic realisation based on fitted parameters (black line) and 500 stochastic outbreak realisations based on the same fitted parameters (grey lines) in Georgia, Hungary, and the United Kingdom. (D) The estimated proportions of individuals no longer susceptible (non-susceptible) to SARS-CoV-2 infection on 01 January 2021. Age-specific immunity level estimates were weighted by population age structure while calculating the country-level immunity levels. Countries marked by crosshatch patterns are those that were not included in the fitting stage; countries marked by the solid grey area outside the WHO European Region. Shapefiles were downloaded from Eurostat GISCO.

Fig. 4

Optimal vaccine prioritisation strategies under different roll-out scenarios and decision-making metrics Main panel — Optimal strategies across the WHO European Region that minimise COVID-19 deaths, cases, losses in comorbidity-adjusted life expectancy (cLE), comorbidity- and quality-adjusted life-years (cQALY), and human capital (HC) as decision-making metrics. All decision-making metrics were summed over 01 January 2021-31 December 2022. Top right inserts within each panel — y-axis: Difference in outcome (totalled over the region) when a given prioritisation strategy is used across the entire WHO European Region compared to if the optimal prioritisation strategy in each country is used (black) x-axis: ranking. Shapefiles are downloaded from Eurostat GISCO ; countries marked by crosshatch patterns are those that were not included in the projection stage; countries marked by solid grey are those outside the WHO European Region. Country-specific results can be found in the Zenodo archive

Fig. 5

Optimal vaccine prioritisation strategies, given different vaccine profiles Optimal strategy for each country and vaccine profile while minimising mortality, morbidity, and losses in comorbidity-adjusted life expectancy (cLE), comorbidity- and quality-adjusted life-years (cQALY), and human capital (HC) for 38 countries in the WHO European Region. All decision-making metrics have been summed over 01 January 2021-31 December 2022. Country-specific results are in Supplemental Figures 19 and 20.