Covid-19: why the disease carries long-term health risks, even after mild forms
Covid-19: why the disease carries long-term health risks, even after mild forms
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"Living with the virus." When it appeared, this slogan described a distant future. It now summarizes the attitude adopted in most European countries, including France, where health restrictions have virtually disappeared. More than 130,000 people are testing positive for Covid-19 every day , a total never reached before the end of 2021, but the subject has disappeared from public debate. Yet the virus has not ceased to be dangerous. It still kills 101 people a day on average, mostly vulnerable or unvaccinated. A series of recent studies has also lifted the veil on its long-term effects: after an infection, the risk of other pathologies increases, even for those who do not present a risk factor,by the long Covid .
In April 2021, a first study by three researchers from the University of Saint-Louis (United States), published by the journal Nature *, identified a myriad of health problems that affected people who had Covid-19 more frequently. . Using an extensive health database of US Army veterans, the authors had compared nearly 5 million non-sick people and 77,000 people who tested positive, starting on the 30th day after their infection. Five months later, they had more respiratory problems and also suffered more "disorders of the nervous and neurocognitive system, mental health, metabolism, cardiovascular, gastrointestinal, malaise, fatigue, musculoskeletal pain and anemia"than people with a similar profile who have never tested positive. Even non-hospitalized patients presented this risk of sequelae.
An increased risk of heart problems
Since then, this database has been used for several studies by the same team, including one on cardiovascular risks, published in February in Nature *. "It shows a risk multiplied by 1.5 or 2 on all events" , not only the well-known cardiac inflammations in patients with Covid-19, observes Ariel Cohen, former president of the French Society of Cardiology. In people who test positive (more than 150,000 have been observed), the risk of stroke is thus multiplied by 1.52 in the year following infection, the risk of pulmonary embolism by 2.93, that of syndrome acute coronary by 1.72.
"At the start of the pandemic, we thought that Covid-19 was simply a source of decompensation for existing risks" , recalls Ariel Cohen. That is to say that people predisposed to these problems declared them on the occasion of an infection by Sars-CoV-2. The results of these American researchers are "a surprise" , he admits.
"This study shows that there is an aggravated risk related to the infection itself and that it does not go away over time as we thought."
Ariel Cohen, former president of the French Society of Cardiologyat franceinfo.fr
If the way in which the virus causes such sequelae is not entirely clear, observation of patients has already shown "that the virus attacks the wall of blood vessels" , which in particular promotes the appearance of clots, explains Olivier Robineau, infectious disease specialist at Tourcoing hospital (North).
On the brain, more blurred symptoms
Patients cured of Covid-19 also have a higher risk of developing kidney-related pathologies, according to a study by the same American team, published in November in the Journal of the American Society of Nephrology *. The data point in particular to a risk of end-stage renal failure multiplied by three in former Covid-19 patients (and by 2.15 in those who have not been hospitalized). Indeed, because it creates vascular problems, the virus can affect a large number of organs. "All these organs are vascularized. As soon as the function of the artery is impaired, there is a risk that they will be affected" , explains cardiologist Ariel Cohen.
In the minds of the general public, Covid-19 is more associated with symptoms like loss of taste and smell. But they point out that the virus also affects the brain and nervous system. Patients with long Covid report in particular difficulty concentrating and a form of "mental fog". A study on the brains of monkeys infected with the virus, published on April 1 in Nature Communications * , showed damage "that can lead to [these] long-term neurological symptoms of long Covid" , including in animals without developed a severe form.
"Researchers warn of a risk of dementia" favored by the damage caused by the virus, reports Olivier Robineau. The authors of an article published by the journal Science * in January, note that the damage observed in some patients "raises the possibility that the infection can accelerate or trigger the future development of neurodegenerative diseases such as Alzheimer's or Parkinson's disease ".
This hypothesis remains for the moment more vague than that of cardiovascular problems, nuance Olivier Robineau, who recalls that these disorders would take years to appear. Health data from American veterans, however, concludes an increased risk of cognitive decline (multiplied by 1.8) or depression (multiplied by 1.39) in the year following infection, according to a study published on February 16 by the British Medical Journal *.
A virus "revealing" cases of diabetes
This statistical approach has limits. A latest study of these data, published on March 21 in The Lancet *, observes that people cured of Covid-19 are more likely (+40%) to develop type 2 diabetes in the following year. The pandemic will leave "a legacy of chronic disease" , says its lead author, Ziyad Al-Aly, in Nature *. Eric Renard, vice-president of the Francophone Diabetes Society, sees no indication that the virus itself causes diabetes.
"The most obvious link is a revelation link. Covid-19 stresses the body, which can reveal latent diabetes."
Eric Renard, vice-president of the Francophone Diabetes Societyat franceinfo.fr
The possibility that the virus is only a trigger is recognized by American scientists and corresponds to what is observed after other infections. Eric Renard does not believe in the risk of an epidemic of type 2 diabetes: "These patients will simply have discovered their diabetes in an unusual way, with insulin treatment from the outset, but they will fall into line." The study has the merit, he judges, of drawing the attention of doctors to the interest of measuring the blood sugar of people cured of Covid-19, especially if they present other risk factors for diabetes.
Diseases "which remain rare"
"We must remain calm" , pleads infectious disease specialist Olivier Robineau. Recent studies show "an indisputable excess risk" of certain pathologies for Covid-19 patients, "but on events which remain rare. We are not going to have an epidemic of pulmonary embolisms." He also recalls that other elements, such as tobacco and diet, are risk factors that weigh much more heavily in the development of cardiovascular disease, for example.
“There is no reason to panic people in whom the infection has resolved and who are doing perfectly well” , adds Jérôme Larché, referent for monitoring the long Covid in Occitania. "Simply, we must encourage them to consult if there is a problem." Before monitoring all people cured of Covid-19, it is already necessary to identify and direct those who face prolonged symptoms, a "big challenge" , he explains. Another priority "is to make up for the delay in the care of many patients because of the pandemic" , recalls cardiologist Ariel Cohen.
The study of the sequelae of Covid-19 is also only in its infancy. Other work will have to confirm them and refine the measurement of the risks caused by Covid-19, on populations more representative than veterans of the American army, an older and male public than the average.
These risks of Covid-19 remain, moreover, according to these same studies, proportional to the severity of the disease: a reassuring observation while the rise of the Omicron variant and vaccination have reduced the proportion of severely affected patients. But for Jérôme Larché, what we know about the after-effects encourages "activating all possible levers to avoid being contaminated, from the vaccine to wearing a mask" . “Covid-19 is anything but a small temporary infection without consequences” , he recalls.
Large studies illustrate the range of potential sequelae of infection. If they need to be refined, they remind us that the circulation of the virus is not without consequences for overall health.
