Mechanism · Neurology
Neuroinflammation
The brain runs its own immune patrol. In long COVID that patrol can stay switched on long after the infection clears, producing a low, persistent inflammation inside the brain. It is one of the most cited explanations for the neurological side of long COVID.
Short version: the brain's immune cells, the microglia, can stay activated after COVID, producing inflammation inside the brain that fits brain fog and related symptoms.
The brain has its own immune system
The brain is patrolled by microglia, immune cells that normally rest quietly. When they sense danger they activate, releasing inflammatory signals. Useful in a real emergency; harmful when the alarm will not switch off. That stuck-on state is neuroinflammation.1
How COVID sets it off
Two routes are described. Inflammatory signals and viral fragments, including the spike protein, can reach the brain when the blood-brain barrier is leaky, and the resulting microglial activation has been seen directly in tissue studies.1, 2
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Why it matters for symptoms
Activated microglia disturb the chemistry that neurons rely on, which fits brain fog, unrefreshing sleep, and the way mental effort can trigger a crash. It connects the brain symptoms to the same inflammation seen elsewhere in the body.3
Where treatment stands
No anti-inflammatory drug is proven to calm long COVID neuroinflammation, and self-medicating carries risks. Pacing mental load remains the dependable tool while trials continue.
What we don't know
Honest about the edges of the evidence. These are open questions, not settled answers.
- How much of the inflammation is driven by viral fragments versus the body's own response.
- Whether it is reversible, and over what timeframe.
- Whether calming microglia would relieve symptoms in people, which no trial has shown.
- How to measure it without specialized research imaging.
- How it relates to the longer-term questions about brain aging.
References
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