Older people remain most at risk of dying from the new coronavirus disease, COVID-19. The majority of people who get COVID-19 have minor or moderate sickness. But "majority" does not mean "all." So, who else should be concerned about contracting severe, even deadly, cases of COVID-19?

It may be months before scientists have enough data to say for sure who, aside from the old, is most at risk and why. But, medical experts have already learned some helpful information from numbers on early cases around the world.

Not just the old getting sick

In China, 80 percent of COVID-19 deaths were among people in their 60s or older.

This alone means some countries face higher percentages of deaths from the disease. Italy has the world's second oldest population after Japan. Italy has reported more than 80 percent of deaths in the country so far were among those 70 or older.

But, "the idea that this is purely a disease that causes death in older people we need to be very, very careful with," said Dr. Mike Ryan. He is the World Health Organization's emergencies chief.

Between 10 and 15 percent of people under 50 have moderate to severe infections, he said last week.

"Young people are not invincible," said the WHO's Maria Van Kerkhove. She noted that more information is needed about the disease in all age groups.

Italy reports 25 percent of its confirmed cases are among people ages 19 to 50. In Spain, about 33 percent are under the age of 44. In the U.S., the Centers for Disease Control and Prevention's first examination of cases found that 29 percent were ages 20 to 44.

Then there is the mystery of how the disease affects children. They have made up a small amount of the world's case counts to date. Most appear to get only mildly ill.

Another question is what part children play in spreading the virus. Researchers at Canada's Dalhousie University recently wrote in The Lancet Infectious Disease publication: "There is an urgent need for further investigation of the role children have in the chain of transmission."

Pre-existing conditions

Along with age, existing health conditions are a major predictor of who suffers most from COVID-19. In China, 40 percent of people who required critical care had health problems before they became infected. COVID-19 deaths in China were highest among people who already had heart disease, diabetes or chronic lung diseases.

Pre-existing health problems can also increase risk of infection. This includes people who have weak immune systems caused by things such as cancer treatment. Additional threats are likely to be discovered.

Italy reported that of the first nine people younger than 40 who died of COVID-19, seven were confirmed to have serious health issues such as heart disease.

Heart disease is a very general term. But, so far, it looks like those most at risk have serious cardiovascular disease such as congestive heart failure or severely blocked or hardened arteries, said Dr. Trish Perl. She is infectious disease chief at UT Southwestern Medical Center.

Arteries are the largest tubes through which blood flows around the body.

Any sort of infection generally makes diabetes harder to control. But it is not clear why diabetics appear to be at greater risk with COVID-19.

As for preexisting breathing diseases, "this is really happening in people who have less lung capacity," Dr. Perl said.

Asthma, a breathing condition that affects 300 million people worldwide, is also a special worry.

The gender mystery

Several countries have observed that men are more likely to get severely sick from COVID-19. This is not a surprise to researchers. During the outbreaks of the coronavirus diseases SARS and MERS, scientists also found that men generally had more severe cases than women.

In China, a little more than half the COVID deaths have been among men. Some other parts of Asia report similar amounts. In Italy, men so far make up 58 percent of infections. And a report on Britain's first 200 coronavirus patients admitted to critical care said that about sixty-five percent were male.

One reason? Worldwide, men are more likely to have smoked more heavily and for longer periods than women. The European Center for Disease Prevention and Control is urging research into smoking's connection to COVID-19.

Sex hormones may be involved also. In 2017, American researchers who infected mice with SARS found that male mice were more likely to die. Estrogen -- a female sex hormone -- seemed protective. When the mice had their ovaries removed, deaths among female mice increased.

I'm Ashley Thompson.

The Associated Press reported this story. Ashley Thompson adapted it for VOA Learning English. Caty Weaver was the editor.

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mild - n. not harsh or severe

invincible - adj. impossible to defeat or overcome

transmission - n. the act or process by which something is spread or passed from one person or thing to another

role - n. a part that someone or something has in a particular activity or situation

diabetes - n. a serious disease in which the body cannot properly control the amount of sugar in your blood because it does not have enough insulin

chronic - adj. continuing or occurring again and again for a long time

immune system - n. the system that protects your body from diseases and infections

asthma - n. a physical condition that makes it difficult for someone to breathe

hormones - n. natural substances produced in the body which influence the way the body grows or develops

ovary - n. one of usually two organs in women and female animals that produce eggs and female hormones