Most people who get the coronavirus will fully recover and go right back to their lives. But the latest research suggests that at least 10 percent have long-term symptoms, even after their body has apparently cleared the virus. <\/p>\n
The condition, known as \u201clong Covid,\u201d has emerged as a scary feature of the pandemic \u2014 a reminder that even as hospitalizations and deaths come down, millions of people will continue to suffer from the aftermath of infection. <\/p>\n
And, as it turns out, \u201cthis isn\u2019t unique to Covid,\u201d Akiko Iwasaki, an immunologist at the Yale School of Medicine, told Vox. <\/p>\n
Instead, Covid-19 appears to be one of many infections, from Ebola to strep throat, that can give rise to stubborn symptoms in an unlucky subset of patients. \u201cIt is more typical than not that a virus infection leads to long-lasting symptoms in some fraction of individuals,\u201d Iwasaki said. <\/p>\n
The difference now is that, with 137 million Covid-19 cases worldwide and counting, long-haulers are more visible: Their suffering has come on in unprecedented numbers. It\u2019s also possible the coronavirus causes long-term symptoms even more frequently than other infections. <\/p>\n
In this week\u2019s episode of Unexplainable<\/em>, we dive into what we know about long Covid and what other viruses can teach us about the condition, including the leading hypotheses for what might be driving symptoms in Covid long-haulers. <\/p>\n \n \n We also look at what we can learn from patients who have been grappling with medically unexplained symptoms \u2014 the kind that don\u2019t correspond to problematic diagnostic test results or imaging \u2014 for years before the pandemic hit. Here\u2019s a rundown of what scientists think could explain the mysterious symptoms, and why even the vaccine might not help. <\/p>\n 1) The virus and \u201cviral ghosts\u201d didn\u2019t actually leave the body<\/p>\n The first explanation for what might cause persistent symptoms in people who\u2019ve been infected with Covid-19 is the simplest: The virus or its components might still be lurking in the body somewhere, long after a person starts testing negative. <\/p>\n We\u2019ve learned from other long-term viral illnesses that, in some cases, pathogens do not fully clear the body. \u201cIt\u2019s out of the blood but gets into tissue in a low level \u2014 the gut, even maybe the brain in some people who are really sick \u2014 and you have a reservoir of the virus that remains,\u201d PolyBio Research Foundation microbiologist Amy Proal told Vox. \u201cAnd that drives a lot of inflammation and symptoms.\u201d<\/p>\n These viral reservoirs have been documented following infections with many other pathogens. During the 2014-2016 Ebola epidemic, studies emerged showing the Ebola virus could linger in the eye and semen. There were similar findings during the 2015-2016 Zika epidemic when health officials warned about the possibility that Zika could be sexually transmitted. (Viral reservoirs are also why the moniker \u201cpost-viral\u201d can be problematic, Proal added.)<\/p>\n A related explanation for what might be happening with long-Covid patients is what Iwasaki calls \u201cviral ghosts.\u201d While the intact virus may have left the body, \u201cthere may be RNA and protein from the virus that\u2019s lingering and continuing to stimulate the immune system,\u201d Iwasaki said. \u201cIt\u2019s almost like having a chronic viral infection \u2014 it keeps stimulating the immune system because the virus or viral components are still there, and the body doesn\u2019t know how to shut it off.\u201d <\/p>\n Recent studies in Nature<\/em> and The Lancet<\/em> documented coronavirus RNA and protein in a variety of body systems, including the gastrointestinal tract and brain. <\/p>\n In autopsies of people with chronic fatigue syndrome, researchers also found enterovirus RNA and proteins in patients\u2019 brains, including, in one case, in the brain stem region. The brain stem controls sleep cycles, autonomic function (the largely unconscious system driving bodily functions, such as digestion, blood pressure, and heart rate), and the flu-like symptoms we develop in response to inflammation and injury. <\/p>\n \u201cIf that area of the brain signaling becomes dysregulated [by viruses],\u201d Proal said, \u201c[that] can result in sets of symptoms that meet a diagnostic criteria for [chronic fatigue syndrome], or even for long Covid.\u201d <\/p>\n 2) Other pathogens lurking in the body reawaken <\/p>\n Other pathogens already lurking in the body prior to a coronavirus infection might also exacerbate symptoms. For example, viruses in the herpes family \u2014 such as Epstein-Barr (the cause of mono) or varicella zoster (the cause of chickenpox and shingles) \u2014 stay dormant in the body forever. Under normal conditions, the immune system can keep them in check. <\/p>\n \u201cSo, for example, 90 percent of people in the world already have herpes viruses,\u201d said Proal. \u201cBut in those patients, the immune system keeps them in a place where they can\u2019t replicate, where they can\u2019t express proteins. They\u2019re kind of controlled.\u201d <\/p>\n But then Covid-19 comes along, and all of a sudden these other viruses get a chance to gain a foothold again. With the immune system tied up fighting Covid-19, the other viruses may reawaken. And they \u2014 not the coronavirus \u2014 drive symptoms. <\/p>\n 3) The immune system turns on the body <\/p>\n Another key hypothesis: Long-Covid patients have developed an autoimmune disorder. The virus interrupts normal immune function, causing it to misfire, so that molecules that normally target foreign invaders \u2014 like viruses \u2014 turn on the body.<\/p>\n These \u201crogue antibodies,\u201d known as autoantibodies, \u201cattack either elements of the body\u2019s immune defences or specific proteins in organs such as the heart,\u201d according to Nature<\/em>. The assault is thought to be distinct from cytokine storm, an acute immune system disorder that appeared as a potential threat early in the pandemic. <\/p>\n \u201cUnder that scenario, we talk about molecular mimicry,\u201d Proal said. \u201cBasically, the virus creates proteins that look like human proteins or tissue, and that kind of tricks the immune system.\u201d Here, the the immune system tries to target the virus, which \u201cif it has a similar size and shape to a human tissue or protein, it fires on the human tissue or protein as well,\u201d she added.<\/p>\n 4) The microbiome gets thrown out of whack <\/p>\n It\u2019s also possible the coronavirus might deplete important microorganisms in the gut microbiome \u2014 the trillions of bacteria, viruses, and fungi that live in and on the body. <\/p>\n In one study, researchers tracked blood and stool samples from 100 patients hospitalized with SARS-CoV-2 infection, testing some up to 30 days after they cleared the virus. (They also collected samples from a control group for comparison.) And they found Covid-19 infection was linked to a \u201cdysbiotic gut microbiome,\u201d even after the virus cleared the respiratory tract; they also hypothesized that it might contribute to the persistent health problems some patients are experiencing.<\/p>\n \u201cUnder conditions of health, those communities are in a state of balance. It\u2019s like a forest, like different organisms are doing different things, but it\u2019s in a harmonious state,\u201d Proal said. But Covid-19 could lead to an imbalance in the microbiome. \u201cAnd a huge number of symptoms are tied to microbiome dysbiosis. Irritable bowel syndrome or even neuro-inflammatory symptoms can be driven by these ecosystems when they go out of balance, too.\u201d <\/p>\n 5) The body is injured<\/p>\n The virus might have cleared the body but left injuries in its wake \u2014 scars in the lungs or damage to the heart, for example \u2014 and these injuries might give rise to symptoms. <\/p>\n According to a recent preprint involving 201 patients, 70 percent had impairments in one or more organs four months after their initial Covid-19 symptoms set in. In other unpublished research, radiologists at the University of Southern California tracked hospitalized patients\u2019 lung recovery using CT scans. They found one-third had scars caused by tissue death more than a month later. Other patients may have brain damage that causes neurological symptoms. <\/p>\n There\u2019s also growing evidence of widespread cardiac injury, even in patients who aren\u2019t hospitalized. In a JAMA Cardiology<\/em> study, researchers performed cardiac MRIs on 100 patients in Germany who had recovered from Covid-19 within the past two to three months. An astounding 78 percent still had heart abnormalities.<\/p>\n<\/div>\n<\/div>\n For coronavirus patients who had to be admitted to intensive care units, there\u2019s a related explanation: Long before the pandemic, the intensive care community coined a term for the persistent symptoms people frequently experience following stays in an ICU for any reason, from cancer to tuberculosis. These symptoms include muscle weakness, brain fog, sleep disturbances, and depression \u2014 the aftermath of a body lying around in a hospital bed for days on end and injuries or side effects from treatments patients received, including intubation. <\/p>\n