Researchers warn of severe long-term damage to the brain after Covid following new study.
Six years on from the outbreak that reshaped the world, Covid continues to cast a long shadow. While many hoped the pandemic would eventually become a closed chapter, mounting scientific evidence suggests that for hundreds of millions of people, the consequences are far from over.
Avindra Nath, clinical director of Neurological Disorders and Stroke at the National Institutes of Health, has been tracking the long-term neurological effects of Covid since the early days of the pandemic.
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“We thought for a long time that once you have it and you’re done with it, that’ll be it,” Nath told Bloomberg in June 2020. “But it turns out that that’s not the case. Thousands of patients now are complaining of the fact that they have persistent symptoms.”
Long Covid has since become one of the fastest-growing diagnoses and one of the most economically disruptive chronic conditions in modern medicine. A study published in December estimated that as many as 400 million people worldwide are living with lasting consequences of a SARS-CoV-2 infection, also known as long-Covid.
However, the research goes beyond fatigue and breathlessness. Large-scale population studies and observational research are suggesting people who contracted Covid face a 'statistically elevated risk of cognitive impairment' compared to matched control groups. In older age groups, the risk extends to 'dementia-level decline', sometimes months or even years after the initial infection.
The correlation was consistent across cognitive testing, health records and symptom surveys.
Alongside this, a study published in January followed essential workers who had provided blood samples both before and after contracting Covid. It found that people who developed long-term neurological symptoms after Covid also showed increased levels of phosphorylated tau, a protein linked to early brain degeneration.
This was especially true when symptoms lasted more than a year.
However, the study's authors stress that the findings do not suggest that Covid directly causes Alzheimer's, but rather that the biological pattern is something to be aware of.
Meanwhile, Nath's research on autopsy findings, imaging studies and long-term clinical assessments has given him reason to believe the virus can accelerate neurodegenerative processes, especially in older patients.
“The incidence and prevalence of Alzheimer’s is going to just escalate,” he says. “It’s a huge public-health problem.”
And the mounting research backs his claim.
A study from NYU Langone Health found that in patients experiencing neurological long-Covid symptoms, a brain structure involved in regulating immune activity and clearing waste showed signs of enlargement and impaired blood flow, which correlated with blood markers linked to Alzheimer's.
And a separate study from October 2024 found that even mild Covid infection could produce subtle but measurable changes in cognition and memory that persisted for at least a year in a small group of volunteers.
At the NIH, Nath is leading a clinical trial that approaches long Covid as an immune-driven neurological condition, testing whether therapies can reduce lingering inflammation and help restore brain function long after Covid has passed.
“There’s something really biologically wrong,” Nath told Bloomberg. “They need to seek help. And if their physicians cannot figure it out, they need to find researchers who are looking into these things.”