A very large new study (n = 335,000, Finland) showed an association between people who had been hospitalized with viral illness and later neurodegenerative disease, including dementia (often within a year but up to 15 years later). The study results were replicated with another very large data set (n = 106,000, U.K.).
Dementia had the most associations, with links to six different virus exposures: viral encephalitis, viral warts, other viral diseases, all influenza, influenza and pneumonia, or viral pneumonia.
The highest hazard ratio was seen for the relationship between viral encephalitis and Alzheimer’s: 30.72 for the discovery (Finnish) cohort, with an odds ratio of 22.06 for the replication (U.K.) cohort.
“To place this in context, we see in FinnGen, 24 of 406 viral encephalitis cases went on to develop Alzheimer’s disease (5.9%); this is higher than the general prevalence of Alzheimer’s disease in the same population at less than 3%.” The Hazard Ratio (HR) compares the probability of the affected group compared with the control group. The change may be significant even if the absolute numbers are low.
“The overwhelming majority of replicated associations include viruses commonly considered neurotrophic (81%), which means they can invade the central nervous system through peripheral nerves or by crossing the blood-brain barrier,” the researchers observed. “This suggests that these viruses may increase neurodegenerative disease risk by lowering cognitive reserve (resilience to neurodegeneration and the ability to carry out complex mental tasks) by contributing to inflammation in the brain.”
The study did not include Covid.
These are nasty viral diseases. They can kill even aside from the new discovery about later neurodegeneration. I get my flu shot every year and have also had the multi-valent pneumonia vaccines. No point taking a chance with this.
Wendy