Eight-in-ten people hospitalised with Covid are left with brain damage, according to new research.
Symptoms range from headaches and loss of sense of smell or taste – to comas and strokes.
Those affected are six times more likely to die from the infection, say scientists.
The shock findings are based on an interim analysis from the Global Consortium Study of Neurologic Dysfunction in Covid-19 (GCS-NeuroCOVID).
Among 3,744 hospitalised adults, an alarming 82 per cent had neurological problems.
Nearly four in 10 reported headaches – and almost a third said they lost their sense of smell or taste.
Of clinically diagnosed syndromes – abnormalities a bedside doctor can observe – acute encephalopathy was most common.
The term refers to general damage to the brain – temporary or permanent conditions that affect its structure or function.
Lead author Professor Sherry Chou said: “Even if the pandemic is completely eradicated, we are still talking about millions of survivors who need our help.
“It is important to find out what symptoms and health problems those patients are facing, and there is still plenty of work for years to come.”
Principal investigator Prof Chou, of the University of Pittsburgh, added: “Acute encephalopathy is by far the most common symptom that we see in the clinic.
“Those patients may be in an altered sensory state or have impaired consciousness, or they don’t feel like themselves and act confused, delirious or agitated.”
It affected almost half the patients – ahead of coma (17 per cent) and strokes (six per cent).
Prof Chou said: “Very early on in the pandemic, it became apparent a good number of people who were sick enough to be hospitalised also develop neurological problems.
“A year later, we are still fighting an unknown invisible enemy and, like in any battle, we need intel – we have to learn as much as we can about neurological impacts of Covid-19 in patients who are actively sick and in survivors.”
But those events were very rare – occurring in less than one percent of cases.
Covid-19 is known to infect the brain and affect the body’s network of neurons.
Now scientists are investigating the long-term impact – to see if the virus causes enduring brain damage.
Having a pre-existing neurological condition – from brain, spinal cord and nerve diseases to chronic migraines or dementia – doubled the risk.
Any neurological symptoms related to the virus – from loss of smell to strokes – was linked to a six-fold higher risk of dying.
But even if a patient beats the odds and recovers, their long-term health outlook is still uncertain, said Prof Chou.
The early results, published in JAMA Network Open, are part of the worldwide effort to gather information about its incidence, severity and outcomes.
It is the largest cohort study of its kind to date – spanning 133 sites across all continents except Antarctica.
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Coronavirus has even been found to directly attack the brain – causing meningitis and brain swelling, or encephalitis.
But those events were very rare – occurring in less than one percent of the cases.
The GCS-NeuroCOVID consortium has attracted collaborators from Europe, North and South America, Asia, the Middle East and Africa.
The cognitive and neurological implications of Covid-19 remain unknown.
But they are of growing concern to doctors, who have found evidence of the virus in the brain, and central nervous system.
A British and US team have launched a research project to see if the infection increases the risk of developing Alzheimer’s.
The full repercussions of brain-related problems caused by coronavirus will not be fully understood for decades as survivors age.
But autopsies, mouse studies and data from other respiratory viruses are cause for concern, researchers have warned.
One study found even people with moderate cases of Covid-19 can suffer strokes and seizures.