PARIS — It started as a mild cough. She had no underlying health issues.

But on March 24, at the age of 16, rather than becoming one of the many coronavirus patients to see their symptoms come and go, Julie became the youngest person in France to die from the disease. Health officials said she contracted a severe form of the virus, which is extremely rare among young people — rare but not impossible.

"People need to stop thinking that the virus only affects the elderly. No one is invincible in the face of this virus," her sister told Le Parisien.

For most, the message had seemed clear: the older you are, the more at risk you are from coronavirus. But even top medical researchers from around the world are still trying to understand the nature of COVID-19, and particularly who is most vulnerable.

In recent days, new data has sparked concern of an increasing number of young people infected around the world, as several deaths of teenagers made headlines in Europe and the U.S.. In their latest media briefing, WHO officials also warned about a surge in cases of young people dying from the virus. "We are seeing more and more younger individuals who are experiencing severe disease," Dr. Maria Van Kerkhove said, "Some of those individuals have had underlying conditions, but some have not."

So what do we know about the "age factor" for COVID-19?

*In Moscow, 56% of new coronavirus cases are younger than 40 years old, reported The Moscow Times. According to the city's coronavirus crisis center, 45% of Moscow's patients in serious condition are younger than 60 years old and nearly 40% of patients younger than 40 years old are on respirators.

No one is invincible in the face of this virus.

*In Australia, people in their 20s have more confirmed cases of COVID-19 than any other age group. The highest share, 11,3% of cases are among people aged 25 to 29, followed by those aged 60 to 65 who make up 9,5% of positive cases, reports The Guardian. Australian experts believe the data might be skewed because people in their 20s are more likely to travel or meet returned travelers. Both testing and infection is therefore more concentrated among this group.

*In Chicago, a nine-month-old became the first infant in the U.S. to die of the disease, while a twelve-year-old girl fell victim to coronavirus in Belgium.

Statistically, it is still proven, that those over 60 are still at highest risk of developing a severe case or dying from the disease. But as Anthony Fauci of the US National Institute of Allergy and Infectious Diseases told BBC, the virus "isn't a mathematical formula", so there are reasons for people in every age group to be cautious.

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