The impact of quality-adjusted life years on evaluating COVID-19 mitigation strategies: lessons from age-specific vaccination roll-out and variants of concern in Belgium (2020-2022)

Abstract

Background: When formulating and evaluating COVID-19 vaccination strategies, an emphasis has been placed on preventing severe disease that overburdens healthcare systems and leads to mortality. However, more conventional outcomes such as quality-adjusted life years (QALYs) and inequality indicators are warranted as additional information for policymakers.

Methods: We adopted a mathematical transmission model to describe the infectious disease dynamics of SARS-COV-2, including disease mortality and morbidity, and to evaluate (non)pharmaceutical interventions. Therefore, we considered temporal immunity levels, together with the distinct transmissibility of variants of concern (VOCs) and their corresponding vaccine effectiveness. We included both general and age-specific characteristics related to SARS-CoV-2 vaccination. Our scenario study is informed by data from Belgium, focusing on the period from August 2021 until February 2022, when vaccination for children aged 5-11 years was initially not yet licensed and first booster doses were administered to adults. More specifically, we investigated the potential impact of an earlier vaccination programme for children and increased or reduced historical adult booster dose uptake.

Results: Through simulations, we demonstrate that increasing vaccine uptake in children aged 5-11 years in August-September 2021 could have led to reduced disease incidence and ICU occupancy, which was an essential indicator for implementing non-pharmaceutical interventions and maintaining healthcare system functionality. However, an enhanced booster dose regimen for adults from November 2021 onward could have resulted in more substantial cumulative QALY gains, particularly through the prevention of elevated levels of infection and disease incidence associated with the emergence of Omicron VOC. In both scenarios, the need for non-pharmaceutical interventions could have decreased, potentially boosting economic activity and mental well-being.

Conclusions: When calculating the impact of measures to mitigate disease spread in terms of life years lost due to COVID-19 mortality, we highlight the impact of COVID-19 on the health-related quality of life of survivors. Our study underscores that disease-related morbidity could constitute a significant part of the overall health burden. Our quantitative findings depend on the specific setup of the interventions under review, which is open to debate or should be contextualised within future situations.

Keywords: COVID-19; Model; Non-pharmaceutical intervention; QALY; SARS-CoV-2; Vaccine.

Fig. 1

Health states and transitions in the two-strain transmission model. The model structure is described in the main text and model parameters are listed in the Supplementary Information

Fig. 2

Overview of the duplicated two-strain model structure to account for vaccine type- and dose-specific immunity against infection and severe disease in combination with differential waning immunity over time. The grey boxes embody the transmission structure included in Fig. 1 while only the Susceptible and Recovered are shown here (with $R_i$ representing $R_a$ and $R_b$). More information on the waning states is included in Table 1

Fig. 3

Reported and scenario-based uptake of COVID-19 vaccines over time in adults above the age of 20y (top) and 0-19-year-old children (bottom). The uptake is presented in terms of the absolute number of doses (left axis) and as a percentage of the target group (right axis)

Fig. 4

Projected daily hospital admissions with COVID-19 in Belgium with adjusted vaccine uptake for 5-11-year old children or adults. The curves represent the time-dependent point-wise average of 400 stochastic realisations, while the 95% credible interval is shown by the shaded area. Related figures on hospital occupancy, ICU load and mortality are included in the Supplementary Information

Fig. 5

Average age-specific QALY gain with the increased childhood vaccination in Jul-Sept 2021 (red, left) and the increased first booster dose uptake in adults by Feb 2022 (blue, right). The effects are presented by illness-related, i.e. due to mild and severe infections, and mortality-related QALY gain

Fig. 6

Sensitivity analysis on the projected QALY gain when assuming 0% or 30% vaccine-effectiveness against transmission and in the absence of the Omicron VOC. Results are shown per vaccine uptake scenario in terms of the mean (cross) and corresponding 95% CrI (whiskers)