More evidence is mounting indicating chronic infection with herpesviruses or SARS-CoV-2 (COVID) being a risk factor for developing dementia. In prior studies, researchers have reported that infection with herpes simplex virus (HSV), varicella-zoster virus (VZV-Shingles), human herpes virus-6 (HHV-6) and SARS-CoV-2 might be a risk factor for developing Alzheimer disease and other forms of dementia. A research study in Wales found a 20% lower risk of dementia in those who received a shingles vaccine compared to those who did not. Viruses raise the risk for dementia.
As for SARS-CoV-2, a new study showed elevated biomarkers for Alzheimer disease including B-amyloid and tau after even mild infection in some people. Amyloid proteins in the brain are associated with neurodegenerative diseases like Alzheimer’s disease and Parkinson’s disease. Whether this infection can infect and kill neurons is unclear, but the virus can activate glial cells (the brains immune cells) and promote neuroinflammation, which then can damage neurons. SARS CoV-2 can also harm the blood-brain barrier and the endothelial vessels in the brain which is linked to several forms of dementia.
There are multiple mechanisms that can explain this link. Low grade chronic neuroinflammation can produce inflammatory molecules that can be neurotoxic. This inflammation in the brain elicits increased production of B-amyloid, which is an anti-microbial peptide that helps to contain acute infection. But if elevated levels of B-amyloid persists long enough, they become neurotoxic.
Immunization against COVID and now herpes viruses have been linked to lower subsequent rates of dementia…
Immunization against COVID and now herpes viruses have been linked to lower subsequent rates of dementia, as has anti-viral treatment in some studies. This of course is one of many compounding factors. Viral infections disrupt the microbiome which houses 60-70% of the immune system. Viruses can activate an autoimmune response by re-activating other dormant viruses such as CMV and EBV. This exacerbates the problem with an already overwhelmed immune system.
Another important factor associated with dementia is sleep. Sleep is the principle driver of glymphatic flow which is the brains plumbing system that consists of a network of fluid filled and water channels along side blood vessels to drain chemical waste, and facilitate movement of cerebrospinal fluid. This clearance of toxic proteins, like B-amyloid, are critical to brain health. The aging brain accumulates metabolic waste. The accumulation of B-amyloid and tau leads to sleep disturbance and dysregulation of the circadian rhythm. This reduced non-REM sleep has been linked to the risk of early Alzheimer’s disease. This appears to be bidirectional, setting up a vicious loop, since decreased sleep leads to more toxic proteins, and the toxic proteins interfere with sleep.
Reference: Eyting, M et al. A natural experiment on the effect of herpes zoster vaccination on dementia. Nature, 641, 438-446 (2025).
Topol, E. Our sleep, brain aging and waste clearance. Ground Truths. Jan 12, 2025.
Feng Y et al. Human herpesvirus-associated trans-posable element activation in human aging brains with Alzheimer’s disease. Alzheimers Dement 2025 Feb; 21:e14595.