As the new coronavirus continues to spread throughout the United States, reports of young people suddenly dying from Covid-19, the disease caused by the virus, are beginning to surface—and health experts aren't exactly sure why that's happening to some, when the disease causes only mild symptoms for most young patients.

Toolkit: Access our resources for a COVID-19 variant surge

Young people are developing Covid-19 at significant rates—and hundreds have died

According to an analysis of state data by the Washington Post, at least 759 people under the age of 50 in the United States had died from Covid-19 as of Wednesday. The Post identified at least 45 deaths among patients in their 20s, at least 190 deaths among patients in their 30s, and at least 413 deaths among patients in their 40s. The Post noted that the actual number of Covid-19 deaths among people younger than 50 is likely higher, as not all states report Covid-19 deaths by age.

CDC data on more than 1,400 hospitalizations related to Covid-19 shows people under the age of 50 accounted for about 25% of the hospitalizations. Most of those people had other underlying health conditions, but at least seven of them did not, CDC said.

The United States isn't the only country seeing large proportions of young people affected by Covid-19. Earlier this month, Maria Van Kerkhove, head of the World Health Organization's emerging diseases and zoonosis unit, said, "We are seeing more and more younger individuals who are experiencing severe disease." She explained, "We've seen some data from a number of countries across Europe where people of younger age have died. Some of those individuals have had underlying conditions, but some have not."

Reports: Key drivers of change for 7 specialty care markets

Why are some healthy, young people dying of Covid-19?

Health experts aren't sure why some otherwise healthy, young people are suddenly dying of Covid-19, but they do have some theories.

One theory is that some people are genetically predisposed to developing more severe cases of Covid-19 than others. For example, Philip Murphy, a biomedical researcher at the National Institute of Allergy and Infectious Diseases, told Science Magazine's Jocelyn Kaiser that variations in a person's ACE2 gene receptor potentially "could make it easier or harder for the virus to get into lung cells."

Michael Skinner, a virologist at Imperial College London, said he believes it's "very possible that some of us could have a particular genetic makeup that makes it more likely that we will respond badly to an infection with this coronavirus."

Another theory is that some patients might have low levels of surfactant, a substance the body produces to help the lungs expand and contract, as a result of the disease. If a patient lacks an adequate amount of surfactant, their lungs will become stiff, which could explain why some patients have trouble breathing even if they're on a ventilator, CNN reports.

There's also a theory that the virus could be causing what's known as a "cytokine storm" in some young patients. The phenomenon, named after cytokine proteins which are part of the immune system, causes the immune system to overreact to an external pathogen, like a virus. The response ultimately could cause a patient's immune system to attack their lungs, causing their lungs to stop delivering oxygen to the rest of their body, and leading to respiratory failure and potentially death.

Other health experts suggest that patients exposed to larger amounts of the new coronavirus could become sicker than others. Alison Sinclair, a virologist at Sussex University, said, "A person with a high viral load has more virus particles than one with a low load. We do not yet know what impact viral load has on the symptoms of a person infected with Covid-19. Whether there is a link between a high viral load and worse outcomes is going to be important to find out."

Case study: Recovery clinics for COVID-19 long-haulers

Younger people becoming more aware of Covid-19's dangers

Whatever the reason, the increasing reports of Covid-19 deaths among healthy, young patients are causing some to start taking the new coronavirus more seriously, Kaiser Health News reports.

KHN reports that, in early March, swarms of college students attended spring break parties throughout the country despite public health experts urging the public to practice social distancing. According to KHN, younger people may have ignored the warnings because, early on, they believed they weren't as vulnerable to the new coronavirus as older people or those with underlying health conditions.

But in recent weeks, more young people have become aware of their vulnerability to the virus, KHN reports.

Laura Mae, a 27-year-old in Milwaukee, was surprised when she developed Covid-19. After going out on March 14, Laura Mae developed a sore throat, fever, chills, shortness of breath, and exhaustion. She contacted a nurse via a local coronavirus hotline and was she was presumptive positive for Covid-19. This meant she should assume she had the disease even though she didn’t qualify for testing.

"It was a complete shock," she said. "I didn't realize that someone like me, a healthy 27-year-old who has no immune issues, could get so sick."

Now, Mae is warning others that they, too, could contract the new coronavirus—and potentially spread it to someone who might not survive Covid-19. "You might be young and healthy and be able to fight this off on your own, but there are people who could end up hospitalized, and it's not a joke," she said. "I was laughing at all the memes and the jokes [about the new coronavirus], and now I'm not. It's real" (Gupta, CNN, 4/6; Walker/Hopkins, Wall Street Journal, 4/9; McKie, The Guardian, 4/9; Mooney et. al., Washington Post, 4/8; Knight, Kaiser Health News, 4/10; Feuer, CNBC, 4/3; Kaiser, Science Magazine, 3/27).