One in five people worldwide have an underlying health condition that puts them at risk for a severe COVID-19 illness if they contract the virus, scientists found.

An estimated 1.7 billion people suffer from conditions ranging from type 2 diabetes to heart disease, according to a study published in The Lancet Global Health. About 349 million of them would probably need to go to the hospital for treatment if they were infected, Andrew Clark, an associate professor at the London School of Hygiene and Tropical Medicine, and colleagues found.

The researchers took risk factors highlighted in official guidelines, including heart disease and diabetes, and used broad epidemiology data such as the Global Burden of Diseases study to arrive at their estimates. Not everyone with an underlying condition would go on to develop severe symptoms, they said.

“It is time to evolve from a one-size-fits-all approach to one that centers on those most at risk,” Nina Schwalbe, a professor at Columbia University’s Mailman School of Public Health, wrote in an accompanying editorial. She called for a better understanding of risk factors including social determinants of health such as income, employment status and education.

Regions with younger populations, such as Africa, present less risk overall despite some spots where the prevalence of HIV and AIDS is high, the authors said. Others like Europe, where average ages are higher and almost a third of people have at least one health condition, may be less resilient. The report also highlighted risks for small island nations where the prevalence of diabetes is high, such as Fiji and Mauritius.