While not demonstrating a causal link, the correlations are pretty striking — good argument for greatly increasing vaccination rates for many viral diseases.
Around 80 percent of the viruses implicated in brain diseases were considered ‘neurotrophic’, which means they could cross the blood-brain barrier. “Strikingly, vaccines are currently available for some of these viruses, including influenza, shingles (varicella-zoster), and pneumonia,” the researchers write. “Although vaccines do not prevent all cases of illness, they are known to dramatically reduce hospitalization rates. This evidence suggests that vaccination may mitigate some risk of developing neurodegenerative disease.” The impact of viral infections on the brain persisted for up to 15 years in some cases. And there were no instances where exposure to viruses was protective.