COVID-19 can damage the brain, causing long-term problems with thinking and memory. New research suggests the damage comes from the immune system's reaction to the coronavirus, not the virus itself.



Scientists are learning that COVID-19 can cause long-term damage to the brain. Problems with memory and thinking may linger for months after an infection. NPR's Jon Hamilton reports that COVID-19 may even increase the risk of Alzheimer's.

JON HAMILTON, BYLINE: Early in the pandemic, people with COVID-19 began reporting an odd symptom - the loss of smell and taste. The reason wasn't congestion. Somehow, the SARS-CoV-2 virus was affecting nerves that carry information from the nose to the brain. Dr. Gabriel de Erausquin is a brain scientist at the Long School of Medicine at UT Health in San Antonio. He says he and his colleagues became worried.

GABRIEL DE ERAUSQUIN: We were afraid, I would say, that SARS-CoV-2 was going to invade the brain.

HAMILTON: De Erausquin says that fear intensified when some COVID-19 patients began reporting symptoms associated with brain damage.

DE ERAUSQUIN: Forgetfulness that interferes with their ability to function. They complain about trouble with organizing their tasks. And that entails things such as being able to prepare a meal.

HAMILTON: So de Erausquin and a team of scientists reviewed dozens of studies about COVID-19's impact on the brain. Their findings appear today in the journal Alzheimer's & Dementia. De Erausquin says it's likely that some patients will face long-term problems.

DE ERAUSQUIN: Even if the proportion - the rate is not very high, the absolute numbers of people who will suffer these consequences is likely to be high.

HAMILTON: COVID-19 can produce blood clots that lead to a stroke, and it can cause lung damage that deprives the brain of oxygen. To understand other mechanisms, though, scientists needed brains from COVID patients who had died. And Dr. Avi Nath of the National Institute of Neurological Disorders and Stroke says early on, they didn't have any.

AVINDRA NATH: Because it was such an infectious organism, people were not conducting autopsies at most places.

HAMILTON: That's changing, though. Nath was part of a team that studied brain tissue from 19 COVID patients. The team saw widespread evidence of inflammation and damage. Nath says they also found a possible explanation.

NATH: What we found was that the very small blood vessels in the brain were leaking. And it wasn't evenly. You would find a small blood vessel here and a small blood vessel there.

HAMILTON: Nath says it was like a series of tiny strokes affecting different areas of the brain. The finding could explain why COVID-19 patients have such a wide range of brain-related symptoms. For some, it's problems with memory and thinking or mood. For others, Nath says, it's problems related to brain areas that control functions like heart rate, breathing and blood pressure.

NATH: They complain of heart racing. When they stand up, they get quite dizzy. They can have, you know, urinary problems.

HAMILTON: Still others report feeling extreme fatigue. Heather Snyder of the Alzheimer's Association says inflammation and leaky blood vessels may also contribute to another brain problem.

HEATHER SNYDER: We know that those are important in Alzheimer's disease, and we're seeing them play a key role here in COVID-19. And what that might mean in later life - we need to be asking that question now.

HAMILTON: So the Alzheimer's Association and researchers from more than 30 countries have formed a consortium to study the long-term effects of COVID-19 on the brain. Snyder says it should help answer some important questions.

SNYDER: What's happening at six months, 12 months, 18 months and going forward in terms of their behavior, their memory, their overall functioning as well.

HAMILTON: And will they develop new brain impairments as they age?

Jon Hamilton, NPR News.

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