Post-COVID condition, or long-COVID does not appear to be linked to direct viral invasion of the brain or active brain damage, according to a study.

Long-COVID is known to persist for several months subsequent to the initial infection. The condition includes various combinations of fatigue, apathy, and difficulties with memory and concentration.

Researchers at the University of Gothenburg in Sweden found that searching for abnormal biomarkers among the participants yielded no hits in either blood or cerebrospinal fluid samples.

The study, published in the Journal of Infectious Diseases, included 25 people with confirmed post-COVID conditions, six people without residual symptoms after COVID-19, and 17 control subjects who were completely free of COVID-19.

The strength of the study lies not in the number of participants, which is fairly limited, but in the fact that they all including the control subjects underwent not only blood tests but also the considerably more invasive procedure of lumbar punctures to collect cerebrospinal fluid.

At the time when the samples were taken, at least three months had passed since the first symptoms of COVID-19 in those who had had the disease. The samples were taken between February and November 2021 and were analysed for a total of 37 different biomarkers.

Notably, the blood and cerebrospinal fluid analyses showed that SARS-CoV-2 antigens were undetectable in all samples. Additionally, there were no significant differences between the groups when analysing blood and cerebrospinal fluid for immune activation or brain injury markers. 

The findings thus suggest that post-COVID condition is not the result of ongoing infection, immune activation, or brain damage.

"The findings enhance our understanding of post-COVID conditions. The results suggest that the condition is more likely a consequence of events that occur during the acute phase of COVID-19, rather than an ongoing viral infection or persistent inflammation of the central nervous system," said Nelly Kanberg, a doctoral student in infectious diseases at the University of Gothenburg's Sahlgrenska Academy.

The extent to which post-COVID conditions can be linked to the body's inflammatory response during the actual infection is unclear. Many studies are currently being carried out around the world, including those that explore risk factors for post-COVID conditions.