An estimated 1,7 billion people (which represents 22% of the world’s population) have at least one underlying health condition that could put them in a coronavirus risk category — and this doesn’t even include factors such as poverty and obesity.

If infected, about 349 million of them would have to go to the hospital for treatment.

More than eight million people worldwide have already been diagnosed with COVID-19 and at least 434,000 have died. But the deaths haven’t been distributed evenly. Those with underlying health conditions, such as heart disease and diabetes, have been much more vulnerable.

In the new study, the researchers established 11 categories of underlying conditions that could raise the risk of severe COVID-19, a form of the symptomatic disease that requires hospitalization, using information from the World Health Organization and health agencies in the United States and Britain.

The list included patients who regularly take immunosuppressive drugs or are undergoing immunity-weakening treatments. But excluded healthy older individuals, at risk of coronavirus due to their age, as well as poverty and obesity, which can play a role in the susceptibility of the person to the disease and the access to health care.

Data from the Global Burden of Disease Study was used by the researchers, a global epidemiological survey done in 2017 to identify the number of individuals with high-risk conditions. Their analysis found than one-fifth of the world’s population may be at increased risk of more severe disease.

Nevertheless, increased risk is not the same as high risk. Not everyone that has a health condition will go to the hospital, the researchers explained. Only 4% of the world’s population would have to be hospitalized if they get infected, the study writes — but that’s still 349 million people.

But the level of risk actually depends on age, gender and geographical location. The risk goes from 1% of people under 20 to about 20% of those aged 70 or older and reaches more than 25% in males over 70. Twice the number of men as women would require hospitalization in all age groups under 65.

Parts of the world with younger populations, such as Africa, have a lower risk overall despite some spots where the prevalence of HIV and AIDS is high, the authors said. Meanwhile, other areas like Europe, where the average age is higher and a third of the people have at least one health condition, could be less resilient.

“The share of the population at increased risk of severe COVID-19 is generally lower in Africa than elsewhere due to much younger country populations, but a much higher proportion of severe cases could be fatal in Africa than elsewhere,” said in a statement Andrew Clark, co-author of the study.

The findings could help government officials focus containment efforts on people vulnerable to the virus’s most dangerous effects and eventually prioritize them for vaccination. When the pandemic started, researchers knew chronic conditions could worsen the disease. Now, there’s a better “understanding of the numbers involved,” Clark said.

The study was published in the journal The Lancet.