This Is Why COVID Kills Some People and Others Are Symptom-Free, Study Says

"This could help explain why some people show milder symptoms of disease while others get severely sick."

At this point in the coronavirus pandemic, one thing has become very clear: A brush with the novel coronavirus is not the same for every patient. The way someone's body is affected by COVID-19 can vary wildly from person to person. And while some end up dying as a result of intense battles with the virus, there are others who somehow manage to never develop so much as a slight fever or minor cough. Now, a new study is shedding light on why some people have hardly any COVID symptoms at all after contracting the virus—and it may have to do with that pesky common cold you dread every year.

Based on the new study published in the journal Science, the presence of the immune system's memory T cells could be the key to understanding why some infected patients remain asymptomatic. Since the common cold is another type of coronavirus, previous exposure to a cold could provide a more efficient rapid immune response, due to T cells recognizing how to essentially deactivate the coronavirus more quickly. This would make some COVID-19 infections a much less arduous fight, and potentially mean less of the typical COVID symptoms others experience.

photo of two black men, one who's coughing and one who's not

"We have now proven that, in some people, pre-existing T cell memory against common cold coronaviruses can cross-recognize SARS-CoV-2, down to the exact molecular structures," co-leader of the study Daniela Weiskopf, PhD, La Jolla Institute for Immunology (LJI) Research Assistant Professor, said in a statement. "This could help explain why some people show milder symptoms of disease while others get severely sick."

The research itself was built heavily upon previous work by fellow LJI scientist Shane Crotty, PhD, whose study found that 40 to 60 percent of people who were never previously exposed to SARS-CoV-2 still had specific T cells that could react to the virus. After studying the connection between people who had been exposed to COVID-19's "less dangerous cousins," analysis showed that patients never previously exposed to the novel coronavirus were able to produce T cells that fought against SARS-CoV-2 as well as four different types of common cold coronaviruses.

"Immune reactivity may translate to different degrees of protection," co-leader of the study Alessandro Sette, PhD, said in a statement. "Having a strong T cell response, or a better T cell response may give you the opportunity to mount a much quicker and stronger response."

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Previous research on the reasons behind severe COVID-19 cases trod heavily on genetic markers such as blood type, the age of the patient, and exactly how the virus enters the body. And while the authors of the new study agree that more research is needed to substantiate their findings, they're also confident that this data could help in developing effectively potent vaccines.

"We knew there was pre-existing reactivity," Sette said. "This study provides very strong direct molecular evidence that memory T cells can 'see' sequences that are very similar between common cold coronaviruses and SARS-CoV-2." And for more on the spread of COVID-19, check out Dr. Fauci Says There's Now Evidence That Coronavirus Spreads This Way.

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Zachary Mack
Zach is a freelance writer specializing in beer, wine, food, spirits, and travel. He is based in Manhattan. Read more
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