The risk of severe COVID-19 disease is known to be higher in older individuals and those with underlying health conditions. Understanding the number of individuals at increased risk of severe COVID-19 illness, and how this varies between countries should inform the design of possible strategies to shield or vaccinate those at highest risk.
We estimated the number of individuals at increased risk (those with at least one condition listed as ‘at increased risk of severe COVID-19 disease’ in current guidelines) by age (5-year age groups), sex and country (n=188) based on prevalence data from the Global Burden of Disease (GBD) study for 2017 and United Nations population estimates for 2020. We also calculated the number of individuals without an underlying condition that could be considered at increased risk because of their age, using minimum ages from 50 to 70 years. The list of underlying conditions relevant to COVID-19 disease was determined by mapping across from the conditions listed in GBD to the guidelines published by WHO and public health agencies in the UK and US. We analysed data from two large multimorbidity studies to determine appropriate adjustment factors for clustering and multimorbidity. To help interpretation of the degree of risk among those at increased risk, we also estimated the number of individuals at high risk (those that would require hospital admission if infected).
We estimate that 1.7 (1.0 - 2.4) billion individuals (22% [15-28%] of the global population) are at increased risk of severe COVID-19 disease due to underlying conditions (ranging from <5% of those aged <20 years to >66% aged 70+ years), and that 349 (186-787) million (4% [3-9%]) are at high risk (ranging from <1% aged <20 years to >25% of males aged 70+ years). The share of the population at increased risk is highest in countries with older age populations, African countries with high HIV/AIDS prevalence and small island nations with high diabetes prevalence. Estimates of the number of individuals at increased risk are most sensitive to the prevalence of chronic kidney disease (CKD), diabetes, cardiovascular disease (CVD) and chronic respiratory disease (CRD).
About one in five individuals worldwide could be at increased risk of severe COVID-19 disease due to underlying health conditions. However, for many of these individuals their condition will not be severe enough to be captured in health systems and their level of increased risk may be quite modest. Indeed, we estimate that about one in 20 individuals could require hospital admission if infected. The degree of risk varies substantially by age and sex, with men aged 70+ years at particularly high risk. Our estimates are uncertain, and focus on underlying conditions rather than other risk factors (ethnicity, deprivation, obesity, occupation, residence etc.) but provide a starting point for considering the number of individuals that may need to be shielded or vaccinated as the global pandemic unfolds.