3 Health Risks of Covid-19 That Are Not Often Discussed


The third, most worrisome one is just recently noted.


As global mass vaccination is going on, we have been fixating on the risks of Covid-19 vaccines. At least I’ve written a number of such articles, namely on the biodistribution of mRNA and DNA vaccines, vaccine-induced blood clots and low platelets, and original antigen sin. But this time, let’s look at the virus (SARS-CoV-2) or disease (Covid-19) more closely.

First, let’s briefly recap what most of us already knows about the health risks of SARS-CoV-2 or Covid-19:

  • It can cause severe pneumonia, blood clots, and multi-organ failure that can hospitalize a person and can be fatal, especially for those who are older and have pre-existing medical conditions.
  • It binds to the ACE2 receptor on human cells easily owing to its unique furin cleavage site, allowing SARS-CoV-2 to infect all sorts of cells from the brain to the toes, making the virus highly infectious and contagious.
  • It can cause the long-COVID or post-COVID syndrome (as elaborated more later), even in young persons who only had non-severe Covid-19,

But SARS-CoV-2 or Covid-19 is capable of so much more than these.

1. Being asymptomatic doesn’t mean that nothing is going on inside the body

SARS-CoV-2 causes asymptomatic (symptomless) infection about 40–45% of the time. But having no observable symptomatic manifestation does not mean that nothing is going on inside the body.

SARS-CoV-2 can still replicate itself in the body of asymptomatic infected persons. On-going viral replication comes with viral shedding, and the shed virus may still infect others. A 2021 study from the U.S. Centers for Disease Control and Prevention (CDC) estimates that asymptomatic persons contribute to 59% of all transmission (i.e., 35% from pre-symptomatic and 24% from never-symptomatic persons).

Asymptomatic infection is also not without any health consequences.

Studies performing chest computed tomography (CT) scans have revealed lung abnormalities in 30–50% of asymptomatic adults infected with SARS-CoV-2. Even in children who got infected asymptomatically, 25% still showed abnormal chest CT scan results in a study. A case series report has also noted similar chest CT abnormalities in 3 out of 4 children with asymptomatic SARS-CoV-2 infection.

CT uses X-ray with computer imaging software to create an image of how an organ looks like. A CT scan is deemed ‘abnormal’ when the imaged organ doesn’t look right, but it doesn't tell us what the specific problem is. An abnormal chest CT scan could mean many things, such as pneumonia, heart failure, lung cancer, tuberculosis, lung scarring, or nothing serious.

Myocarditis (inflamed heart muscle) has also been observed via magnetic resonance imaging (MRI) in 78% (out of 100) of recovered Covid-19 patients, including those who were asymptomatic. Their hearts also showed signs of tissue scarring and reduced blood pumping efficiency. And these problems were absent in the control group (SARS-CoV-2-negative). Another cardiac MRI study of 26 young athletes with asymptomatic SARS-CoV-2 also found that 15% showed myocarditis and 30% showed cardiac scarring.

Similar to CT, abnormal MRI results could also mean nothing worrisome. “This may be clinically inconsequential, or it could lead to chronic effects,” Anthony Fauci, MD, director of the National Institute of Allergy and Infectious Diseases and chief medical advisor for the White House, said.

But a separate study reported only 1.4% of student-athletes (2 out of 145) who recovered from non-severe Covid-19 had abnormal cardiac MRI results. Another newer study examined 149 health care workers who had non-severe Covid-19 and 75 who never had Covid-19 (control group). And although they noted cardiac MRI abnormalities in about 10% of participants, this outcome was not significantly different between the Covid-19 and control groups.

These latter two studies suggest that post-Covid heart problems may not be as common as we thought. But we also cannot dismiss the studies (discussed earlier) that have found otherwise. So, in sum, even mild or asymptomatic Covid-19 could sometimes lead to lung and heart abnormalities.

Although “they were very mild abnormalities, that doesn't mean they weren’t real,” Patricia Bandettini, MD, a senior researcher at the National Heart, Lung, and Blood Institute, said. Other experts theorized thatorgan reserve” — where a healthy organ has some reserve or capacity to withstand some amount of damage and continue to function normally — may be at play.

But at this point, nobody knows for sure if such heart and lung abnormalities have any long-term health consequences. After all, there’s a lesser incentive to study more or less healthy people, unless problems arise.

Image by Freepik

2. Long-COVID can disrupt daily activities, affect children, and last for years

Many of us have heard of the long-haulers — now called long-COVID or post-COVID syndrome — who suffer multi-organ symptoms for many months after Covid-19. Theories on the biological cause(s) of long-COVID include viral persistence, immune system dysfunction, and residual organ damage such as persistent brainstem dysfunction or lung scarring. The WHO and U.K. Office for National Statistics (ONS) has estimated that 10% of Covid-19 cases — hospitalized or not — will turn into long-COVID.

Its common symptoms include fatigue, breathlessness, cognitive impairment (brain fog, attention or memory problems), headache, muscle pain, joint pain, heart palpitations, cough, chest pain, etc. Although these symptoms can be manageable, they also can be serious to the point of disrupting normal day-to-day lives.

In a 6-month follow-up study of 183 previously hospitalized persons for Covid-19, 56% developed long-COVID. Of this 56%, 31% had no difficulties doing their usual daily activities, 15% faced some limitations, 7% could not do some activities, and 3% became dependent on caregivers. Before Covid-19, 85% of the survivors were healthy; after Covid-19, it’s down to 44% at 6-month.

A survey study of 3,762 Covid-19 survivors found that 45% needed a reduced work schedule than pre-Covid life, and 22% were not working when taking the survey due to long-COVID. The respondents took the survey at about 6–7 months after Covid-19, and 92% of them had non-severe Covid-19 that needed no hospitalization. But this study distributed the surveys to online support groups, so the sampling is not random.

Unfortunately, even children are not spared from long-COVID. A case series identified five children aged 8–15 who manifested multi-organ symptoms at 6–8 months following Covid-19 diagnosis. Later, in a survey study of 150 children who developed long-COVID, symptoms persisted for 8 months or more. And 83% of the children had changes in energy levels, 59% in mood, 56% in sleep, and 50% in appetite compared to pre-Covid life at 8-month.

Another study looked at 129 children survivors of Covid-19 from a university hospital in Rome and found 53% developed long-COVID at a 5-month follow-up. But 53% prevalence may be an overestimate. The U.K. ONS, on the other hand, has estimated that 13–15% of children (aged 2–16 years) will face persistent symptoms for at least five weeks after getting Covid-19. That said, current studies are still limited to draw any firm conclusions about how often children develop long-COVID, as well as how serious it is and how long it lasts.

From these studies, it appears that long-COVID can persist for up to 7 months or more. Some have already lived with long-COVID for over a year. This begs the question: how long will full recovery take? Although we still don't know the answer, we can infer hints from its predecessor, SARS-1.

According to a 4-year follow-up study on 181 SARS survivors (average age of 43 years) from Hong Kong, 40% still suffer from fatigue, 27.1% had chronic fatigue syndrome per the CDC criteria, and 42.5% had at least one psychiatric disorder— e.g., posttraumatic stress disorder, depression, and somatoform pain disorder — per the Diagnostic and Statistical Manual of Mental Disorders (fourth edition). And these clinical outcomes were not influenced by sex, socioeconomic status, pre-existing comorbidities, or initial SARS severity.

Even at a 15-year follow-up, a study performed chest CT scans and lung function tests on 35 SARS survivors from China and noted impaired total lung capacity and gas exchange efficiency in 37% of them. Yes, even after 15 years. So, we shouldn’t be surprised if long-COVID will last for years too.

Image by Freepik

3. Covid-19 increases the risks of other diseases in the future

This health risk was just recently noted, at least more recent than the other two, and it’s also more serious.

For a study published in March 2021, researchers in the U.K. followed 47,780 Covid-19 survivors (average age of 64.5 years) from hospital discharge for the next 140 days. From a pool of 50 million, another group of 47,780 persons was selected to match for age, sex, comorbidities, ethnicity, and socioeconomic status to ensure fair comparisons with the Covid-19 group.

Within the 140-day period, what they found is disturbing: 29.6% received a respiratory disease diagnosis, 29.4% got re-hospitalized, and 12.3% died in the Covid-19 group — equating to the respective risks of 6-, 3.5-, and 7.7-times greater than the control group. These numbers were only 5.4%, 9.2%, and 1.7%, respectively, in the control group. And Covid-19 also up the risks of cardiovascular disease, chronic liver disease, chronic kidney disease, and diabetes diagnoses by 3-, 2.8-, 1.9-, and 1.5-times, respectively, compared to controls. However, this study mainly looked at hospitalized persons, so the findings may not generalize to the healthier populations. In fact, the study’s analyses showed that the risks mainly apply to those older than 70 years.

Still, this is not to say that young persons who got mild Covid-19 are free of this worry either. In another study published in March 2021, 201 persons with long-COVID (45 years on average; 80% had mild Covid-19) were followed for about 140 days. Compared to healthy controls, 70% of the long-COVID group had at least one organ imaging abnormalities, and 29% had at least two; namely in the heart (26%), lungs (11%), kidneys (4%), liver (28%), pancreas (40%) and spleen (4%). But this study did not investigate if these organ abnormalities will heal completely or lead to other diseases in the future.

One month later, a separate study published in Nature (a world-ranking journal) arrived at similar conclusions. Using the U.S. national healthcare databases, this study compared 73,435 non-hospitalized Covid-19 survivors to a control group of 4,990,835 non-Covid, non-hospitalized persons to learn what happened in the next six months after Covid-19.

After adjusting for age, sex, and many other variables, results revealed that Covid-19 survivors were at 1.59-times (59%) greater risk of death within the next six months. Specifically, 22.8 per 1000 persons in the Covid-19 group and 14.4 per 1000 persons in the control group died, equating to an excess of 8 deaths per 1000 persons at 6-months. (Note that this is discounting those who have died early from Covid-19, the non-survivors.) Moreover, in this study, Covid-19 survivors face excess burden from other illnesses:

  • Respiratory symptoms or use of benzodiazepines (anti-anxiety drug): excess of 20–30 cases per 1000 persons at 6-month.
  • Neurological symptoms, fatigue, muscle pain, sleep or metabolic disorders, or the use of non-opioid analgesics, antilipidemics, or blood thinners: excess of 10–20 cases per 1000 persons at 6-month.
  • Respiratory failure, lower respiratory tract disease, neurological, anxiety, stress-related, gastrointestinal or skin disorders, diabetes, obesity, anemia, or the use of opioid analgesics or antidepressants: excess of 3–10 cases per 1000 persons at 6-month.
  • Conditions unrelated to Covid-19 (e.g., cancer, accidents, fitting of dental or hearing devices): no excess burden; that is, similar rates between Covid-19 and non-Covid groups.

The Nature study has also investigated how survivors previously hospitalized for Covid-19 (n = 13,654) versus influenza (n =13,997) fare in the next 150 days. Adjusted for relevant variables like age and sex, Covid-19 survivors had a 1.5-times greater risk of death — amounting to an excess of 28.8 deaths per 1000 persons at 5-month — than influenza survivors. Compared to influenza, Covid-19 survivors also had more excess cases — ranging from 5–45 cases per 1000 persons at 5-month — of metabolic, neurological, cardiovascular, blood clotting, gastrointestinal, and fatigue disorders. And there were no differences between Covid-19 and influenza survivors when it comes to unrelated events such as cancers or accidents.

Overall, the three studies presented in this section show that Covid-19 survivors — hospitalized or not — are at increased risks of other diseases in the coming months. While it’s true that only randomized trials can prove cause and effect, it is not right to give people Covid-19 for the sake of research. As these studies have used proper control groups, it is very tough to deny that Covid-19 is not responsible for the study results. So, it is all the more crucial now, especially for Covid-19 survivors, to prioritize our health.

What infectious diseases can do

Does this mean that Covid-19 is a one-of-a-kind infectious viral disease that can cause unique health problems? Not really. Yes, the three abovementioned health problems may be specific to Covid-19, but other infectious diseases also come with their lesser-known complications.

Herpes simplex virus type-1 (HSV-1), for example, causes cold sores (blisters) in the lips. But not many know HSV-1 also increases the risk of Alzheimer’s disease, a memory disorder, to some extent. As HSV-1 hides in the trigeminal nerve near the mouth permanently, HSV-1 can reactivate and cause cold sores when the person is stressed emotionally or physically (weakened immune system or surgery). The reactivated HSV-1 can also hurt neurons in the brain, especially in the hippocampus, where memories are stored. Other microbes that can harm memory function include the human immunodeficiency virus (HIV-1), hepatitis C virus, Porphyromonas gingivalis, and a few others.

Long-COVID is a form of post-viral chronic illness, which is not unique to Covid-19. Prior coronavirus diseases, SARS and the Middle East respiratory syndrome (MERS), can cause similar post-viral illnesses. The CDC has also stated that one in ten people infected with Epstein-Barr virus, Ross River virus, or Coxiella burnetti will develop myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Other infections linked to ME/CFS include human herpesvirus 6, rubella, enterovirus, Candida albicans, and HIV-1.

All in all, infectious diseases like Covid-19 are often capable of causing more problems than we thought. Maybe there are more side effects of Covid-19 — or any infectious diseases for that matter — that are yet to be exposed. Microbes like viruses and bacteria have long been drivers of human and animal evolution for millions of years, so it’s not surprising to see that microbes have far-reaching impacts on our health and biology.

This article was previously published in Microbial Instincts with minor modifications.

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MSc Biology student | 5x first-author academic papers | 100+ articles on coronavirus | Freelance medical writer


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