Burden of Disease Methods: A Guide to Calculate COVID-19 Disability-Adjusted Life Years

Abstract

Background To date, most efforts to understand the comparative population health impact of COVID-19 have been made using mortality-based metrics [1,2]. This has intensified discussion over methodological choices; in particular, how we value the life-years prematurely lost due to COVID-19 [3]. So far, the direct impact of COVID-19 on population health has varied across countries, with wide variation in incidence and infection fatality rates [4]. Understanding and quantifying the combined impact of morbidity and mortality is a key step to standardizing comparisons across countries, and to quantify the within-country impact of COVID-19 relative to other causes of disease and injury, sub-national areas or demographics [5]. This can be achieved by estimating summary measures of population health like disability-adjusted life years (DALYs). The estimation of DALYs is useful to provide comprehensive and comparative public health intelligence to inform decision-making for the management of the COVID-19 pandemic, particularly around the extent of direct and indirect consequences [6]. At present, the Global Burden of Disease (GBD) study has not integrated COVID-19. Some studies have already estimated DALYs due to COVID-19. The first published assessment was performed for Korea, up until the end of April 2020 [7]. An assessment, using a similar time frame, followed for Italy [8]. To date, published studies have only included one COVID-19 related health state, or disability weights were country-specific [7–9]. Aim Our paper provides a step-by-step guide to define COVID-19 as a cause of disease burden, which can be used to calculate DALYs. Additionally, we suggest pragmatic data inputs, reflecting that availability and quality of data inputs will vary by country. This paper builds on previous DALY calculation guides [10,11]. As our paper provides suggestions for different solutions, we recommend that users should be clear about their methodological choices to aid comparisons and knowledge translation. Methodology The impact of COVID-19 on health occurs through two main pathways: directly, as an infectious disease; and indirectly, as a risk factor, for example, through increases in mental health issues due to national lockdowns or delays to surgery, follow-ups and diagnoses through restrictions to vital healthcare services [6]. A group within COST Action (European Cooperation in Science and Technology) CA18218—European Burden of disease Network—convened to establish a common methodological approach to estimate DALYs directly due to COVID-19. This paper presents the developed consensus approach in three steps. The first relates to defining study parameters. The steps that follow relate to estimating the impact of morbidity, in terms of years lived with disability (YLD); and mortality, in terms of years lost to premature mortality (YLL). DALYs quantify the full population health impact and are calculated by summing YLD and YLL. DALYs can be estimated based on grouped characteristics of interest, such as demographics (e.g. age, sex, socioeconomic status, and ethnicity), geographical region, or time.