More than 15% of people who developed COVID-19 would still have at least one symptom six
months older. In France, this would concern several hundred thousand people. The societal
consequences are important. The symptoms are very polymorphic; they evolve in a
fluctuating fashion and persist for several months. Neurological symptoms are often in
the foreground and include different symptoms, among which:

- Cognitive disorders (psychic slowing down, lack of clarity in thought, difficulty in
remembering certain facts, difficulty in performing double tasks, difficulty in
finding words).

- Sensory disturbances such as burning or tingling with or without root topography,
dizziness.

- Neurovegetative manifestations: sudden tachycardia, palpitations, vasomotor
disorders, excessive sweating, digestive disorders or post prandial malaise,
feelings of malaise (lipothymia with or without hypotension), dyspnea or a feeling
of dyspnea, urinary disorders

- Sleep disorders (insomnia, sleep fragmentation, nightmares or hypersomnia)

- Tension type headaches.

The mechanisms explaining the occurrence of these symptoms are still debated. An
important result is the recent demonstration by the UK's National Statistics Office that
people with "long COVID" may, for some, remain carriers of the SARS-CoV-2 virus for
several months. So far, viral persistence has only been demonstrated in a few specific
cases of immunocompromised people, almost all of them having been hospitalized.

Recently, in a pilot study conducted jointly by the Institut Pasteur and AP-HP, we
demonstrated that viral RNA could be found in immunocompetent patients with prolonged
neurological symptoms after COVID-19 (Melo et al 2021). This study concerned 4 patients
explored by micro-brushing the mucous membrane of the olfactory cracks under local
anesthesia more than 4 months after the initial COVID-19. In all patients, SARS-CoV-2 RNA
persisted in significant amounts.

Although this demonstration currently only concerns a small number of people, this study
provides evidence that the virus can remain hidden in the olfactory cracks (a tissue that
is part of the nervous system), including in people with PCR nasopharyngeal and / or
SARS-CoV-2 serology become negative. This persistence of the virus after a so-called
"acute" infection is not unique. In EBOLA virus disease, some people have been shown to
keep the virus in their semen for several months.

It is now necessary to determine whether this persistence is specific to long COVID, what
are the mechanisms and the consequences of this persistence of the virus.

One of the hypotheses is that the virus would persist in endothelial cells and / or
support cells. Intermittent reactivation of the virus would lead to intermittent
inflammation, secretion of pro-inflammatory cytokines, activation of coagulation and
innate immunity cells (monocytes, mast cells, astrocytes, cerebral glial cells) or
adaptive This activation could be due to origin of possible micro-thrombosis responsible
for a decrease in the oxygen supply in the tissues. This tissue hypoxia could cause the
intermittent "brain fog" complained about by patients and the cerebral hypo-metabolisms
seen on CT scans. The virus could infect other cells as well, and the issue of direct
infection of neurons remains unresolved.

In this study, we want to assess whether viral persistence is specific to patients with
prolonged symptoms following COVID-19, to assess whether the presence of SARS-CoV-2 RNA
is correlated with the ability of the virus to replicate, study the cellular
abnormalities associated with the presence of viruses, and correlate the observed
cellular and virological abnormalities with the clinical profile of patients.

We are interested in central neurological disorders, in particular cognitive disorders,
because they are often in the foreground, and they are by far the most disabling symptoms
for patients.