Influenza Vaccine Reduces Dementia Risk
The influenza vaccine has been shown to reduce the risk of dementia, with the strongest evidence demonstrating a 31% relative risk reduction in older adults who receive regular influenza vaccination. 1
Evidence from High-Quality Research
The most recent and comprehensive meta-analysis of 6 cohort studies involving over 2 million participants found that influenza vaccination reduces dementia risk by 31% (RR = 0.69,95% CI: 0.57-0.83) over 4-13 years of follow-up. 1 This represents robust evidence from multiple large populations with consistent findings across studies.
A 2022 propensity-matched cohort study of nearly 1 million matched pairs demonstrated that influenza vaccination reduced Alzheimer's disease risk by 40% (RR = 0.60,95% CI: 0.59-0.61), with an absolute risk reduction of 3.4% and a number needed to treat of 29.4. 2 This means that for every 29 people vaccinated against influenza, one case of Alzheimer's disease is prevented over 4 years of follow-up.
Additional Vaccines Associated with Dementia Risk Reduction
While influenza vaccine has the strongest evidence, other routine adult vaccinations also show protective associations:
Pneumococcal vaccine reduces Alzheimer's disease risk by 27% (RR = 0.73,95% CI: 0.71-0.74) in adults aged 65 and older. 3
Tetanus-diphtheria-pertussis (Tdap) vaccine reduces dementia risk by 42% (HR = 0.58,95% CI: 0.54-0.63) in two independent cohorts with different demographic characteristics. 4
Herpes zoster vaccine reduces Alzheimer's disease risk by 25% (RR = 0.75,95% CI: 0.73-0.76) in older adults. 3
Mechanism and Clinical Implications
The protective effect appears to be mediated through nonspecific anti-inflammatory effects rather than pathogen-specific immunity, as multiple different vaccine types show similar risk reductions. 4 This suggests that vaccination may reduce chronic neuroinflammation, which is a key driver of neurodegenerative disease.
The American Diabetes Association guidelines note that influenza vaccination reduces diabetes-related hospital admissions by 79% during flu epidemics, and the CDC recommends influenza vaccines for all individuals with diabetes. 5 Control of cardiovascular risk factors, including through vaccination strategies, has been associated with reduced risk of incident dementia in older adults with diabetes. 5
Guideline-Based Recommendations for Vaccination
All adults aged 65 years and older should receive annual influenza vaccination, with the added benefit of substantial dementia risk reduction beyond the direct protection against influenza complications. 5
The influenza vaccine has been shown to reduce pneumonia by 53%, hospitalization by 50%, and mortality by 68% in older adults, while also reducing all-cause mortality during influenza season by 27-54%. 5 These cardiovascular and mortality benefits likely contribute to the observed dementia risk reduction.
Important Clinical Considerations
The protective effect is strongest in adults aged 60-75 years, with some attenuation in those over 75 years or in predominantly male populations, though benefit remains significant across all age groups. 1
Patients with dementia are at greater risk of complications from respiratory infections and can benefit from vaccinations, though they are paradoxically less likely to receive them. 6 Community-dwelling dementia patients have lower vaccination rates than those in residential care facilities. 6
Healthcare professionals should actively promote influenza vaccination in older adults, emphasizing both the immediate protection against influenza complications and the long-term benefit of reduced dementia risk. 6
Common Pitfalls to Avoid
Do not dismiss patient concerns about vaccine side effects—the vaccine does not contain live virus and cannot cause influenza. 5 Local soreness and mild systemic symptoms lasting 1-2 days are common but not disabling. 5
Do not withhold vaccination from patients who already have dementia—they remain at high risk for influenza complications and mortality, and vaccination reduces both morbidity and mortality in this population. 6
Do not assume that one year of vaccination is sufficient—the dementia risk reduction is associated with regular, repeated annual vaccination over multiple years. 1, 2