One in five people have underlying health condition increasing risk of severe COVID-19, estimates suggest

An estimated 1.7 billion people, 22 percent of the world population, have at least one underlying health condition that could increase their risk of severe novel coronavirus (COVID-19) if infected, according to a new modeling study published in the journal The Lancet Global Health.

Although the estimates provide an idea of the number of people governments should prioritize for protective measures, not all individuals with these conditions would go on to develop severe symptoms if infected. The authors estimate that 4 percent of the world's population, 349 million of 7.8 billion people, would require hospitalization if infected, suggesting that the increased risk of severe COVID-19 could be quite modest for many with underlying conditions.

Guidelines published by the World Health Organization and by public health agencies in the United States and United Kingdom identify risk factors for severe COVID-19, including cardiovascular disease, chronic kidney disease, diabetes, and chronic respiratory disease.

The new study uses data from 188 countries and provides global, regional, and national estimates for the number of people with underlying health conditions. The authors caution that they focused on underlying chronic conditions and didn't include other possible risk factors for COVID-19 that are not yet included in all guidelines, such as ethnicity and socioeconomic deprivation. Their estimates are therefore unlikely to be exhaustive but serve as a starting point for policymakers.

The authors based their estimates on disease prevalence data from the Global Burden of Diseases, Injuries and Risk Factors Study (GBD) 2017, United Nations population estimates for 2020, and the list of underlying health conditions relevant to COVID-19, as defined by current guidelines. The authors point out that the GBD prevalence estimates are likely to be higher than those from national databases because they're designed to capture cases that might be undiagnosed or not severe enough to be included in electronic health records. They analyzed the number of people with an underlying condition by age group, sex, and country for 188 countries.

To help determine the degree of increased risk, the researchers also provided separate estimates of the proportion of all people with and without underlying conditions who would require hospitalization if infected. The authors calculated those at high risk using infection hospitalization ratios for COVID-19 and made adjustments for differences between countries.

Countries and regions with younger populations have fewer people with at least one underlying health condition, while those with older populations have more people with at least one condition. For example, the proportion of the population with one or more health condition ranges from 16 percent in Africa (283 million people out of 1.3 billion) to 31 percent in Europe (231 million out of 747 million).

Small island nations with high diabetes prevalence, such as Fiji and Mauritius, have among the highest proportion of people with an underlying condition. In Africa, countries with the highest HIV/AIDS prevalence, such as eSwatini and Lesotho, have a greater proportion of people with an underlying condition than countries with lower prevalence, such as Niger.

Globally, less than 5 percent of people aged under 20 years, but more than 66 perfcent of those aged 70 and above, have at least one underlying condition that could increase their risk of severe COVID-19. Among the working age population of 15 to 64 years old, 23 percent are estimated to have at least one underlying condition. The prevalence of one or more condition listed on current guidelines is similar between the sexes, but the authors said they assumed males were twice as likely as females to require hospitalization if infected.

The authors estimate that 349 million people worldwide are at high risk of severe COVID-19, meaning they would require hospital treatment if infected. This risk varies from less than 1 percent of people under 20 to nearly 20 percent of those aged 70 or older, rising to more than 25 percent in males over 70. In all age groups under 65, around twice the number of men as women would require hospitalization. Above 65 years, the ratio becomes less marked because women are over-represented in older age groups due to longer life expectancy.

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