Can shingles increase the risk of dementia or Alzheimer's disease?

Shingles and Risk of Dementia or Alzheimer's Disease

Recent evidence strongly suggests that shingles vaccination is associated with a reduced risk of developing dementia, including Alzheimer's disease. 1

Association Between Shingles and Dementia

• While there has been theoretical concern about a link between herpes zoster virus (shingles) and neurodegenerative disorders, the direct relationship between shingles infection itself and increased dementia risk remains somewhat unclear 2
• A UK Biobank study found a small but non-significant increase in dementia risk in subjects with shingles diagnosed 3 or more years prior to dementia diagnosis (OR: 1.088,95% CI: 0.978-1.211) 2
• Infectious diseases in general may confer a risk of Alzheimer's disease, potentially through activation of dormant herpes viruses including herpes zoster virus (HZV) 3

Protective Effect of Shingles Vaccination

• The recombinant shingles vaccine (Shingrix) is associated with a significantly lower risk of dementia in the 6 years post-vaccination 1
• Receiving the recombinant vaccine is associated with a 17% increase in diagnosis-free time, translating into 164 additional days lived without a dementia diagnosis 1
• The live shingles vaccine (Zostavax) has also shown protective effects:
  • UK Biobank data demonstrated that Zostavax vaccination was associated with significantly decreased risk of dementia (OR: 0.808,95% CI: 0.657-0.993) 2
  • A Welsh population study found vaccinated individuals had reduced risk of dementia (adjusted hazard ratio: 0.72,95% CI: 0.69-0.75) 4

Mechanism of Protection

• The AS01 adjuvant used in the recombinant shingles vaccine may play a direct role in lowering dementia risk 5
• Protection against viral infections may be beneficial to the brain by preventing activation of dormant herpes viruses that could trigger neurodegenerative processes 3
• The association between shingles vaccination and reduced dementia was stronger for vascular dementia than for Alzheimer's disease in some studies 4

Clinical Implications

• The recombinant shingles vaccine (Shingrix) is considered safe for immunocompromised patients, unlike the live vaccine (Zostavax) 6
• Shingrix requires two doses administered 2-6 months apart for optimal protection 6
• The vaccine remains effective for at least 8 years after administration, although effectiveness gradually wanes over time 6

Considerations for Different Patient Populations

• For immunocompromised patients, the recombinant vaccine (Shingrix) is recommended as it is not a live vaccine and poses no risk of vaccine-induced infection 6
• The protective effect of shingles vaccination against dementia has been observed in both men and women, though some research suggests the effect may be greater in women 1
• Patients on TNF inhibitors or other immunosuppressive therapies have an increased risk of developing herpes zoster, making vaccination particularly important for this group 6

Future Research Directions

• These findings should stimulate studies investigating the mechanisms underpinning the protection against dementia 1
• A large-scale randomized control trial could confirm the additional benefit of the recombinant shingles vaccine beyond preventing shingles 1
• Further research is needed to determine if the dementia risk-reducing effects of various vaccinations (flu, pneumonia, and shingles) might be cumulative 3