Three months ago, the 28-year-old postdoctoral research associate from Newcastle, United Kingdom, was on the road with friends in a band as they toured venues in the French Alps.

He came down with Covid-19 symptoms, and like many coronavirus patients, spent weeks in bed.

Unlike other people, however, Green's life hasn't returned to normal.

"Since then it's been on and off with extreme tiredness and fatigue," he said.

Every day he has brain fog, difficulty concentrating and problems with short-term memory that make reading, writing and speaking harder.

"Breathing has been very difficult," he said. "I don't feel like I have my full breath capacity. If I go for a walk for one minute, I'll be really exhausted."

The profound mark the disease has made on Green's life isn't uncommon.

"About 80% are going to experience a mild or asymptomatic version of Covid. It's the other 20% that we're worried about," said Dr. Luis Ostrosky-Zeichner, a professor of medicine at the University of Texas McGovern Medical School.

"One out of five patients are going to get a severe form of the disease."

Some young people are not getting better

As case counts among young people rise, Green and others in their 20s want to share stories of the wreckage Covid-19 has wrought in their lives.

Those patients can potentially experience permanent lung damage, including scarring and reduced lower respiratory capacity.

"The thing that we don't yet fully appreciate is what happens when you get infected, and you get serious disease, and you recover?" said Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, at the BIO International Convention in June.

"We don't know the extent of full recovery or partial recovery, so there's a lot we need to learn," he said.

Young people, who are less likely to die from coronavirus than their grandparents, are an important target of those lessons.

Whether they contracted the virus among the snow-capped peaks of the Alps or in the heart of the outbreak in New York City's borough of Queens, some 20-somethings are getting sick from Covid-19. And staying sick.

Their stories are a warning from millennials to millennials: Don't play the odds with coronavirus because this disease could permanently damage your body.

"What I like to tell my students and patients is that this is a lottery you do not want to win," said Ostrosky-Zeichner.

Read more: What we know now about Covid-19 symptoms (and what to do)

A 28-year-old postdoc feels like a leper

At home in Newcastle, Green is in his fourth month of Covid-19 aftermath.

He has a doctor's note saying that he shouldn't return to full-time work, but he picks up an occasional project when he can. There isn't much else to do resting in bed.

The symptoms are lingering, and they're severe.

"Two weeks ago I had a crushing sensation in my chest," he said. "It felt like I couldn't breathe. That was the worst pa