Two recent studies provide possible explanations for the causes of long-term COVID-19, a syndrome that remains a mystery, one evoking the subsequent combined effect of the virus in different organs, and the other the course of its effect on brain cells.

Christopher Brightling, co-author of a study published Friday in The Lancet Respiratory Medicine, said there was "concrete evidence of changes in various organs of the body" after hospitalisation for Covid-19.

The study relied on an MRI performed on 259 patients hospitalized with COVID-19 in 2020 and 2021, and compared the results with tests conducted on about fifty people who were not infected at all.


Nearly a third of COVID-19 patients tested for "abnormalities" in many organs several months after leaving the hospital, including the brain, lungs, kidneys, and, to a lesser extent, the heart and liver.

For example, the researchers observed damage to the brain's white matter, a phenomenon that the scientific literature can link to a slight cognitive decline.

The study's authors and independent observers said the findings provide a possible explanation for long-term COVID-19 disease or the persistence of subsequent effects several months after infection.

This syndrome, which lacks a consensual definition among scientists, is still not understood at the physiological level, with several explanations, none of which are definitive.

The study, published on Friday, notes that long-term COVID-19 "is not explained by serious deficiencies concentrated in one organ" but rather "an interaction between at least two (different) organ dysfunctions," notes pulmonologist Matthew Baldwin, who was not involved in the study.

Brain pathway

The other study, published a week ago in the journal Biomedicine, focused on the impact of the disease on the brain.

The study, conducted by a team from France's National Institute of Health and Medical Research (INSERM), examined about 50 patients, some of whom experienced low testosterone levels linked to a virus change in some neurons that regulate reproductive functions.

The researchers measured the cognitive functions of these patients and observed impaired performance when this class of neurons was affected by the disease.

"These findings suggest that infection can lead to the death of these neurons and be the cause of certain symptoms that persist over time," the French National Institute of Health and Medical Research said in a press release.

Starting with fatigue, cough, shortness of breath, intermittent fever, loss of taste or smell, difficulty concentrating, and depression, long-term COVID-19 manifests itself as one or more symptoms from a long list generally within three months after infection and lasts at least two months, and these symptoms cannot be explained by other diagnoses and have an impact on the patient's daily life.

In France, 19% of adults or 4.2 million people over 06 years of age have been diagnosed with long-term COVID-18, and a small percentage (1.2%) said they face serious barriers to performing their daily activities, according to a study conducted by the French public health authority in autumn 2022 and published in June.

But symptoms improve slowly after two years in the vast majority of patients (90%) with long-term COVID-19, while others experience rapid improvement or, conversely, persist their disorders, according to a study published in May by Dr. Viet Thi Tran, an epidemiologist at the University of Paris-Cité, of 2197,19 patients with long-term COVID-<> who underwent regular follow-up.