Impact of herpes zoster vaccination on incident dementia: A retrospective study in two patient cohorts

Associations of infections and vaccines with Alzheimer's disease point to a role of compromised immunity rather than specific pathogen in AD

INTRODUCTION

Diverse pathogens (viral, bacterial, fungal) have been associated with Alzheimer's disease (AD) and related traits in various studies. This suggests that compromised immunity, rather than specific microbes, may play a role in AD by increasing an individual's vulnerability to various infections, which could contribute to neurodegeneration. If true, then vaccines that have heterologous effects on immunity, extending beyond protection against the targeted disease, may hold a potential for AD prevention.

METHODS

We evaluated the associations of common adult infections (herpes simplex, zoster (shingles), pneumonia, and recurrent mycoses), and vaccinations against shingles and pneumonia, with the risks of AD and other dementias in a pseudorandomized sample of the Health and Retirement Study (HRS).

RESULTS

Shingles, pneumonia and mycoses, diagnosed between ages 65 and 75, were all associated with significantly increased risk of AD later in life, by 16 %-42 %. Pneumococcal and shingles vaccines administered between ages 65-75 were both associated with a significantly lower risk of AD, by 15 %-21 %. These effects became less pronounced when AD was combined with other dementias.

DISCUSSION

Our findings suggest that both the pneumococcal polysaccharide vaccine and the live attenuated zoster vaccine can offer significant protection against AD. It remains to be determined if non-live shingles vaccine has a similar beneficial effect on AD. This study also found significant associations of various infections with the risk of AD, but not with the risks of other dementias. This indicates that vulnerability to infections may play a more significant role in AD than in other types of dementia, which warrants further investigation.

New approaches for understanding the potential role of microbes in Alzheimer's disease

Alzheimer's disease (AD) involves a complex pathological process that evolves over years, and its etiology is understood as a classic example of gene-environment interaction. The notion that exposure to microbial organisms may play some role in AD pathology has been proposed and debated for decades. New evidence from model organisms and -omic studies, as well as epidemiological data from the recent COVID-19 pandemic and widespread use of vaccines, offers new insights into the "germ hypothesis" of AD. To review new evidence and identify key research questions, the Duke/University of North Carolina (Duke/UNC) Alzheimer's Disease Research Center hosted a virtual symposium and workshop: "New Approaches for Understanding the Potential Role of Microbes in Alzheimer's disease." Discussion centered around the antimicrobial protection hypothesis of amyloid accumulation, and other mechanisms by which microbes could influence AD pathology including immune cell activation, changes in blood-brain barrier, or direct neurotoxicity. This summary of proceedings reviews the content presented in the symposium and provides a summary of major topics and key questions discussed in the workshop.

Herpesviridae, Neurodegenerative Disorders and Autoimmune Diseases: What Is the Relationship between Them?

Alzheimer's disease and Parkinson's disease represent the most common forms of cognitive impairment. Multiple sclerosis is a chronic inflammatory disease of the central nervous system responsible for severe disability. An aberrant immune response is the cause of myelin destruction that covers axons in the brain, spinal cord, and optic nerves. Systemic lupus erythematosus is an autoimmune disease characterized by alteration of B cell activation, while Sjögren's syndrome is a heterogeneous autoimmune disease characterized by altered immune responses. The etiology of all these diseases is very complex, including an interrelationship between genetic factors, principally immune associated genes, and environmental factors such as infectious agents. However, neurodegenerative and autoimmune diseases share proinflammatory signatures and a perturbation of adaptive immunity that might be influenced by herpesviruses. Therefore, they might play a critical role in the disease pathogenesis. The aim of this review was to summarize the principal findings that link herpesviruses to both neurodegenerative and autoimmune diseases; moreover, briefly underlining the potential therapeutic approach of virus vaccination and antivirals.

Vaccines and Dementia: Part II. Efficacy of BCG and Other Vaccines Against Dementia

 There is growing awareness that infections may contribute to the development of senile dementia including Alzheimer's disease (AD), and that immunopotentiation is therefore a legitimate target in the management of diseases of the elderly including AD. In Part I of this work, we provided a historical and molecular background to how vaccines, adjuvants, and their component molecules can elicit broad-spectrum protective effects against diverse agents, culminating in the development of the tuberculosis vaccine strain Bacille Calmette-Guérin (BCG) as a treatment for some types of cancer as well as a prophylactic against infections of the elderly such as pneumonia. In Part II, we critically review studies that BCG and other vaccines may offer a measure of protection against dementia development. Five studies to date have determined that intravesicular BCG administration, the standard of care for bladder cancer, is followed by a mean ∼45% reduction in subsequent AD development in these patients. Although this could potentially be ascribed to confounding factors, the finding that other routine vaccines such as against shingles (herpes zoster virus) and influenza (influenza A virus), among others, also offer a degree of protection against AD (mean 29% over multiple studies) underlines the plausibility that the protective effects are real. We highlight clinical trials that are planned or underway and discuss whether BCG could be replaced by key components of the mycobacterial cell wall such as muramyl dipeptide. We conclude that BCG and similar agents merit far wider consideration as prophylactic agents against dementia.

Associations of infections and vaccines with Alzheimer's disease point to a major role of compromised immunity rather than specific pathogen in AD

INTRODUCTION

Diverse pathogens (viral, bacterial, fungal) have been linked to Alzheimer's disease (AD) indicating a possibility that the culprit may be compromised immunity rather than particular microbe. If true, then vaccines with broad beneficial effects on immunity might be protective against AD.

METHODS

We estimated associations of common adult infections, including herpes simplex, zoster (shingles), pneumonia, and recurrent mycoses, as well as vaccinations against shingles and pneumonia, with the risk of AD in a pseudorandomized sample of the Health and Retirement Study.

RESULTS

Shingles, pneumonia, and mycoses diagnosed between ages 65-75, were all associated with higher risk of AD later in life, by 16%-42%. Pneumococcal and shingles vaccines received between ages 65-75 both lowered the risk of AD, by 15%-21%.

DISCUSSION

Our results support the idea that the connection between AD and infections involves compromised immunity rather than specific pathogen. We discuss mechanisms by which the declining immune surveillance may promote AD, and the role of biological aging in it. Repurposing of vaccines with broad beneficial effects on immunity could be a reasonable approach to AD prevention. Pneumococcal and zoster vaccines are promising candidates for such repurposing.

Severity of posttraumatic stress disorder, type 2 diabetes outcomes and all-cause mortality: A retrospective cohort study

BACKGROUND

Some evidence suggests patients with comorbid PTSD and type 2 diabetes (T2D) have worse T2D outcomes than those with T2D alone. However, there is no evidence regarding PTSD severity and risk for starting insulin, hyperglycemia, microvascular complications, and all-cause mortality.

METHODS

In this retrospective cohort study, Veterans Health Affairs (VHA) medical record data from fiscal year (FY) 2012 to FY2022 were used to identify eligible patients (n = 23,161) who had a PTSD diagnosis, ≥1 PTSD Checklist score, controlled T2D (HbA1c ≤ 7.5) without microvascular complications at baseline. PTSD Checklist for DSM-5 (PCL-5) scores defined mild, moderate, and severe PTSD. Competing risk and survival models estimated the association between PTSD severity and T2D outcomes before and after controlling for confounding.

RESULTS

Most (70%) patients were ≥ 50 years of age, 88% were male, 64.2% were of white race and 17.1% had mild, 67.4% moderate and 15.5% severe PTSD. After control for confounding, as compared to mild PTSD, moderate (HR = 1.05; 95% CI:1.01-1.11) and severe PTSD (HR = 1.15; 95%CI:1.07-1.23) were significantly associated with increased risk for microvascular complication. Hyperarousal was associated with a 42% lower risk of starting insulin. Negative mood was associated with a 16% increased risk for any microvascular complication. Severe PTSD was associated with a lower risk for all-cause mortality (HR = 0.76; 95%CI:0.63-0.91).

CONCLUSIONS

Patients with comorbid PTSD and T2D have an increased risk for microvascular complications. However, they have lower mortality risk perhaps due to more health care use and earlier chronic disease detection. PTSD screening among patients with T2D may be warranted.

Anxiety disorders, benzodiazepine prescription, and incident dementia

BACKGROUND

Prescribing benzodiazepines to older patients is controversial. Anxiety disorders and benzodiazepines have been associated with dementia, but literature is inconsistent. It is unknown if anxiety treated with a benzodiazepine, compared to anxiety disorder alone is associated with dementia risk.

METHODS

A retrospective cohort study (n = 72,496) was conducted using electronic health data from 2014 to 2021. Entropy balancing controlled for bias by indication and other confounding factors.

PARTICIPANTS

Eligible patients were ≥65 years old, had clinic encounters before and after index date and were free of dementia for 2 years prior to index date. Of the 72,496 eligible patients, 85.6% were White and 59.9% were female. Mean age was 74.1 (SD ± 7.1) years.

EXPOSURE

Anxiety disorder was a composite of generalized anxiety disorder, anxiety not otherwise specified, panic disorder, and social phobia. Sustained benzodiazepine use was defined as at least two separate prescription orders in any 6-month period.

MAIN OUTCOME AND MEASURES

ICD-9 or ICD-10 dementia diagnoses.

RESULTS

Six percent of eligible patients had an anxiety diagnosis and 3.6% received sustained benzodiazepine prescriptions. There were 6640 (9.2%) incident dementia events. After controlling for confounders, both sustained benzodiazepine use (HR 1.28, 95% CI: 1.11-1.47) and a diagnosis of anxiety (HR 1.19, 95% CI: 1.06-1.33) were associated with incident dementia in patients aged 65-75. Anxiety disorder with sustained benzodiazepine, compared to anxiety disorder alone, was not associated with incident dementia (HR 1.18, 95% CI: 0.92-1.51) after controlling for confounding. Results were not significant when limiting the sample to those ≥75 years of age.

CONCLUSIONS

Benzodiazepines and anxiety disorders are associated with increased risk for dementia. In patients with anxiety disorders, benzodiazepines were not associated with additional dementia risk. Further research is warranted to determine if benzodiazepines are associated with a reduced or increased risk for dementia compared to other anxiolytic medications in patients with anxiety disorders.

The association of herpes zoster and influenza vaccinations with the risk of developing dementia: a population-based cohort study within the UK Clinical Practice Research Datalink

BACKGROUND

Dementia affects ability to remember, think, or make decisions that interfere with doing everyday activities. There is no cure, therefore any prevention or delay of the onset is of importance. This study aims to investigate the association between zoster and influenza vaccinations and the risk of developing dementia.

METHODS

We conducted a retrospective population-based cohort study using electronic health records from 1469 general practices contributing to the Clinical Practice Research Datalink (CPRD) Aurum database with linked hospital episode statistics (HES) and Office for National Statistics (ONS) mortality records. We built two 'matched cohorts': zoster vaccine (854,745 exposed individuals) matched with 8.8 million comparators without a history of zoster vaccination, and influenza vaccine (742,487 exposed individuals) matched with 7.12 million comparators without a history of vaccination as another comparator group. The cohorts were then followed to assess the association of exposure (vaccine) with outcome (dementia diagnosis).

RESULTS

Zoster vaccination was associated with a lower risk of dementia diagnosis (adjusted hazard ratio (HR) 0.78 with 95% CI: 0.77-0.79), Alzheimer's diagnosis (adjusted HR 0.91 with 95% CI: 0.89-0.92 and other types of dementia (adjusted HR 0.71 with 95% CI: 0.69-0.72). Influenza vaccination also was associated with a slightly reduced hazard of dementia risk (adjusted HR 0.96 with 95% CI: 0.94-0.97).

CONCLUSION

Both zoster vaccine for prevention of shingles / herpes zoster and influenza vaccine to prevent influenza were associated with diminished risk of dementia, with the zoster association appearing more pronounced.

Maintaining brain health across the lifespan

Across the lifespan, the human body and brain endure the impact of a plethora of exogenous and endogenous factors that determine the health outcome in old age. The overwhelming inter-individual variance spans between progressive frailty with loss of autonomy to largely preserved physical, cognitive, and social functions. Understanding the mechanisms underlying the diverse aging trajectories can inform future strategies to maintain a healthy body and brain. Here we provide a comprehensive overview of the current literature on lifetime factors governing brain health. We present the growing body of evidence that unhealthy alimentary regime, sedentary behaviour, sleep pathologies, cardio-vascular risk factors, and chronic inflammation exert their harmful effects in a cumulative and gradual manner, and that timely and efficient intervention could promote healthy and successful aging. We discuss the main effects and interactions between these risk factors and the resulting brain health outcomes to follow with a description of current strategies aiming to eliminate, treat, or counteract the risk factors. We conclude that the detailed insights about modifiable risk factors could inform personalized multi-domain strategies for brain health maintenance on the background of increased longevity.

The role of Bacillus Calmette-Guérin administration on the risk of dementia in bladder cancer patients: a systematic review and meta-analysis

Background

Previous cohort studies have found an association between Bacillus Calmette-Guérin (BCG) administration and incident dementia. In the systematic review and meta-analysis, we aimed to summarize the current evidence of the effect of BCG use on the risk of developing dementia.

Methods

We searched six databases until 20 May 2023 for studies investigating the risk of dementia and BCG administration. Hazard ratios (HRs) and 95% confidence intervals (95% CIs) were pooled in the meta-analysis. Meta-regression, subgroup, and sensitivity analysis were conducted as well.

Results

Of the 4,043 records initially evaluated, five articles were included for final analysis, with a total of 45,407 bladder cancer (BC) patients. All five studies were evaluated and rated as with high quality, and a low possibility of publication bias was indicated. A significant association between BCG and the incidence of dementia in BC patients was found in all five studies. Although a high heterogeneity (I2 = 84.5%, p < 0.001) was observed, the pooled HR was 0.55 (0.42-0.73), indicating that BCG exposure or treatment reduced the risk of incident dementia by 45%. Moreover, the sensitivity analysis showed good robustness of the overall effect with no serious publication bias.

Conclusion

BCG administration is associated with a significantly lower risk of developing dementia. However, an epidemiological cohort is needed to establish a relationship between BCG use and incident dementia in the normal population. Once the relationship is confirmed, more people may benefit from the association.

Systematic review registration

identifier: CRD42023428317.

Programmed ageing: decline of stem cell renewal, immunosenescence, and Alzheimer's disease

The characteristic maximum lifespan varies enormously across animal species from a few hours to hundreds of years. This argues that maximum lifespan, and the ageing process that itself dictates lifespan, are to a large extent genetically determined. Although controversial, this is supported by firm evidence that semelparous species display evolutionarily programmed ageing in response to reproductive and environmental cues. Parabiosis experiments reveal that ageing is orchestrated systemically through the circulation, accompanied by programmed changes in hormone levels across a lifetime. This implies that, like the circadian and circannual clocks, there is a master 'clock of age' (circavital clock) located in the limbic brain of mammals that modulates systemic changes in growth factor and hormone secretion over the lifespan, as well as systemic alterations in gene expression as revealed by genomic methylation analysis. Studies on accelerated ageing in mice, as well as human longevity genes, converge on evolutionarily conserved fibroblast growth factors (FGFs) and their receptors, including KLOTHO, as well as insulin-like growth factors (IGFs) and steroid hormones, as key players mediating the systemic effects of ageing. Age-related changes in these and multiple other factors are inferred to cause a progressive decline in tissue maintenance through failure of stem cell replenishment. This most severely affects the immune system, which requires constant renewal from bone marrow stem cells. Age-related immune decline increases risk of infection whereas lifespan can be extended in germfree animals. This and other evidence suggests that infection is the major cause of death in higher organisms. Immune decline is also associated with age-related diseases. Taking the example of Alzheimer's disease (AD), we assess the evidence that AD is caused by immunosenescence and infection. The signature protein of AD brain, Aβ, is now known to be an antimicrobial peptide, and Aβ deposits in AD brain may be a response to infection rather than a cause of disease. Because some cognitively normal elderly individuals show extensive neuropathology, we argue that the location of the pathology is crucial - specifically, lesions to limbic brain are likely to accentuate immunosenescence, and could thus underlie a vicious cycle of accelerated immune decline and microbial proliferation that culminates in AD. This general model may extend to other age-related diseases, and we propose a general paradigm of organismal senescence in which declining stem cell proliferation leads to programmed immunosenescence and mortality.

Virus exposure and neurodegenerative disease risk across national biobanks

With recent findings connecting the Epstein-Barr virus to an increased risk of multiple sclerosis and growing concerns regarding the neurological impact of the coronavirus pandemic, we examined potential links between viral exposures and neurodegenerative disease risk. Using time series data from FinnGen for discovery and cross-sectional data from the UK Biobank for replication, we identified 45 viral exposures significantly associated with increased risk of neurodegenerative disease and replicated 22 of these associations. The largest effect association was between viral encephalitis exposure and Alzheimer's disease. Influenza with pneumonia was significantly associated with five of the six neurodegenerative diseases studied. We also replicated the Epstein-Barr/multiple sclerosis association. Some of these exposures were associated with an increased risk of neurodegeneration up to 15 years after infection. As vaccines are currently available for some of the associated viruses, vaccination may be a way to reduce some risk of neurodegenerative disease.

The impact of continuous wireless monitoring on adverse device effects in medical and surgical wards: a review of current evidence

Novel technologies allow continuous wireless monitoring systems (CWMS) to measure vital signs and these systems might be favorable compared to intermittent monitoring regarding improving outcomes. However, device safety needs to be validated because uncertain evidence challenges the clinical implementation of CWMS. This review investigates the frequency of device-related adverse events in patients monitored with CWMS in general hospital wards. Systematic literature searches were conducted in PubMed and Embase. We included trials of adult patients in general hospital wards monitored with CWMS. Our primary outcome was the frequency of unanticipated serious adverse device effects (USADEs). Secondary outcomes were adverse device effects (ADEs) and serious adverse device effects (SADE). Data were extracted from eligible studies and descriptive statistics were applied to analyze the data. Seven studies were eligible for inclusion with a total of 1485 patients monitored by CWMS. Of these patients, 54 patients experienced ADEs (3.6%, 95% CI 2.8-4.7%) and no USADEs or SADEs were reported (0%, 95% CI 0-0.31%). The studies of the SensiumVitals® patch, the iThermonitor, and the ViSi Mobile® device reported 28 (9%), 25 (5%), and 1 (3%) ADEs, respectively. No ADEs were reported using the HealthPatch, WARD 24/7 system, or Coviden Alarm Management. Current evidence suggests that CWMS are safe to use but systematic reporting of all adverse device effects is warranted.

The Impact of Routine Vaccinations on Alzheimer's Disease Risk in Persons 65 Years and Older: A Claims-Based Cohort Study using Propensity Score Matching

BACKGROUND

Accumulating evidence suggests that adult vaccinations can reduce the risk of developing Alzheimer's disease (AD) and Alzheimer's disease related dementias.

OBJECTIVE

To compare the risk for developing AD between adults with and without prior vaccination against tetanus and diphtheria, with or without pertussis (Tdap/Td); herpes zoster (HZ); or pneumococcus.

METHODS

A retrospective cohort study was performed using Optum's de-identified Clinformatics® Data Mart Database. Included patients were free of dementia during a 2-year look-back period and were≥65 years old by the start of the 8-year follow-up period. We compared two similar cohorts identified using propensity score matching (PSM), one vaccinated and another unvaccinated, with Tdap/Td, HZ, or pneumococcal vaccines. We calculated the relative risk (RR) and absolute risk reduction (ARR) for developing AD.

RESULTS

For the Tdap/Td vaccine, 7.2% (n = 8,370) of vaccinated patients and 10.2% (n = 11,857) of unvaccinated patients developed AD during follow-up; the RR was 0.70 (95% CI, 0.68-0.72) and ARR was 0.03 (95% CI, 0.02-0.03). For the HZ vaccine, 8.1% (n = 16,106) of vaccinated patients and 10.7% (n = 21,417) of unvaccinated patients developed AD during follow-up; the RR was 0.75 (95% CI, 0.73-0.76) and ARR was 0.02 (95% CI, 0.02-0.02). For the pneumococcal vaccine, 7.92% (n = 20,583) of vaccinated patients and 10.9% (n = 28,558) of unvaccinated patients developed AD during follow-up; the RR was 0.73 (95% CI, 0.71-0.74) and ARR was 0.02 (95% CI, 0.02-0.03).

CONCLUSION

Several vaccinations, including Tdap/Td, HZ, and pneumococcal, are associated with a reduced risk for developing AD.

Infections, Vaccinations, and Risk of Alzheimer's Disease (AD)/Dementia: Probable Involvement of Reactivated Herpes Simplex Virus Type 1

Infections are associated with cognitive decline and increased risk of AD/dementia (Sochocka M, Zwolinska K, Leszek J. Curr Neuropharmacol 15:996-1009, 2017; Ou YN, Zhu JX, Hou XH, Shen XN, Xu W, Dong Q, et al. J Alzheimers Dis 75:299-309, 2020; Sipilä PN, Heikkilä N, Lindbohm JV, Hakulinen C, Vahtera J, Elovainio M, et al. Lancet Infect Dis 21:1557-1567, 2021; Damiano RF, Guedes BF, de Rocca CC, de Padua Serafim A, Castro LHM, Munhoz CD, et al. Eur Arch Psychiatry Clin Neurosci 272:139-154, 2022), and some studies have shown that vaccinations, such as BCG, against a variety of infections decrease the risk. Several reports have described an association of varicella zoster virus (VZV) with AD, and in an epidemiological study, we found that shingles, a disease caused by VZV, conferred a small increased AD/dementia risk, while vaccination against the disease led to a greatly decreased risk - subsequently confirmed by others (Lophatananon A, Mekli K, Cant R, Burns A, Dobson C, Itzhaki R, Muir K, BMJ Open 11:e045871, 2021a; Lehrer S, Rheinstein PH. In Vivo 35:3271-3275, 2021; Scherrer JF, Salas J, Wiemken TL, Hoft DF, Jacobs C, Morley JE. PLoS One 16:e0257405, 2021).

Maintaining a 'fit' immune system: the role of vaccines

INTRODUCTION

Conventionally, vaccines are thought to induce a specific immune response directed against a target pathogen. Long recognized but poorly understood nonspecific benefits of vaccination, such as reduced susceptibility to unrelated diseases or cancer, are now being investigated and may be due in part to "trained immunity'.

AREAS COVERED

We discuss 'trained immunity' and whether vaccine-induced 'trained immunity' could be leveraged to prevent morbidity due to a broader range of causes.

EXPERT OPINION

The prevention of infection i.e. maintaining homeostasis by preventing the primary infection and resulting secondary illnesses, is the pivotal strategy used to direct vaccine design and may have long-term, positive impacts on health at all ages. In the future, we anticipate that vaccine design will change to not only prevent the target infection (or related infections) but to generate positive modifications to the immune response that could prevent a wider range of infections and potentially reduce the impact of immunological changes associated with aging. Despite changing demographics, adult vaccination has not always been prioritized. However, the SARS-CoV-2 pandemic has demonstrated that adult vaccination can flourish given the right circumstances, demonstrating that harnessing the potential benefits of life-course vaccination is achievable for all.

Vaccination Against Pneumonia May Provide Genotype-Specific Protection Against Alzheimer's Disease

Vaccine repurposing that considers individual genotype may aid personalized prevention of Alzheimer's disease (AD). In this retrospective cohort study, we used Cardiovascular Health Study data to estimate associations of pneumococcal polysaccharide vaccine and flu shots received between ages 65-75 with AD onset at age 75 or older, taking into account rs6859 polymorphism in NECTIN2 gene (AD risk factor). Pneumococcal vaccine, and total count of vaccinations against pneumonia and flu, were associated with lower odds of AD in carriers of rs6859 A allele, but not in non-carriers. We conclude that pneumococcal polysaccharide vaccine is a promising candidate for genotype-tailored AD prevention.

Incident Herpes Zoster and Risk of Dementia: A Population-Based Danish Cohort Study

BACKGROUND AND OBJECTIVES

Herpes zoster (HZ) is caused by reactivation of the neurotrophic varicella-zoster virus (VZV). Zoster may contribute to development of dementia through neuroinflammation, cerebral vasculopathy, or direct neural damage, but epidemiologic evidence is limited. We used data from linked nationwide Danish registries to conduct a cohort study of the association between zoster and dementia during 1997-2017. As secondary aims, we examined whether associations were more pronounced for zoster involving cranial nerves (mainly ophthalmic zoster) or the CNS and Alzheimer disease as an outcome.

METHODS

We included people aged ≥40 years with zoster and a general population comparison cohort matched 5:1 by sex and birth year. We identified zoster and dementia in the registries using prescription records in the community and hospital diagnoses. We used Cox regression to compute confounder-adjusted hazard ratios (HRs) with 95% CIs for dementia associated with zoster during 0-1 year and 1-21 years of follow-up. We compared the cumulative incidence of dementia, inverse probability weighted for confounders.

RESULTS

The study included 247,305 people with zoster and 1,235,890 matched general population comparators (median age 64 years; 61% female). The HR of all-cause dementia was 0.98 (95% CI 0.92-1.04) during the first year and 0.93 (95% CI 0.90-0.95) thereafter in people with zoster vs matched comparators. Dementia was diagnosed in 9.7% of patients with zoster and 10.3% of matched comparators by the end of follow-up. We observed no increased long-term risk of dementia in subgroup analyses, except possibly in people with CNS infection (HR 1.94; 95% CI 0.78-4.80). Analyses of Alzheimer disease as a separate outcome showed similar results.

DISCUSSION

HZ is not associated with an increased risk of dementia, and contrary to expectation, we found a small decrease in the risk. The explanation for this finding is unclear, and systematic errors should be considered. Patients with CNS involvement had an almost 2-fold increased relative risk of dementia. The population attributable fraction of dementia due to this rare complication is estimated at 0.014%. Therefore, universal vaccination against VZV in the elderly is unlikely to reduce dementia risk.

Association between human herpesvirus 6 (HHV-6) and cognitive function in the elderly population in Shenzhen, China

AIM

Human herpesvirus 6 (HHV-6) is neurophilic, and its relationship with Alzheimer's disease (AD) remains controversial. This study aimed to examine the relationships between HHV-6 and cognitive abilities in elderly people aged 60 years or above from communities in Shenzhen.

METHODS

We recruited participants from 10 community health service centers in Shenzhen. Participants were divided into case and control groups according to Mini-Mental State Examination (MMSE) scale standards and were included in this study with 1:1 matching based on sex and age (± 3 years). The HHV-6 gene was detected by real-time fluorescent quantitative PCR, and the HHV-6 copy number was quantified.

RESULTS

A total of 580 participants (cases, n = 290; controls, n = 290), matched for gender and age was included in this study. A positive HHV-6 test was not associated with a significant difference in global cognitive performance (OR_adjusted = 1.651, 95% CI = 0.671-4.062). After adjusting for gender, age, education, Pittsburgh Sleep Quality Index (PSQI) score, homocysteine (Hcy) and glycosylated hemoglobin (HbA1c), the results of multiple linear regression showed that there was a statistically negative correlation between HHV-6 copy number and orientation (β_adjusted = -0.974, p = 0.013), attention and calculation (β_adjusted = -1.840, p < 0.001), and language (β_adjusted = -2.267, p < 0.001). The restricted cubic spline (RCS) model results showed that there was a nonlinear dose-response relationship between HHV-6 log10-transformed copies and orientation (p_overall = 0.003, p_nonliner = 0.045), attention and calculation (p_overall < 0.001, p_nonliner < 0.001), and language (p_overall < 0.001, p_nonliner = 0.016).

CONCLUSIONS

HHV-6 infection significantly associated with orientation, attention and calculation, and language in elderly individuals.

Bacillus Calmette–Guérin in Immuno-Regulation of Alzheimer’s Disease

Bacillus Calmette–Guérin is frequently the treatment of choice of superficial bladder cancer. Exposing the urinary bladder of elderly patients with bladder cancer to the BCG vaccine reduced the risk of Alzheimer’s disease (AD) substantially. Vaccines against other infectious microorganisms by other vaccination methods showed a similar but a lesser effect. This suggests that immune effects on AD are antigenically non-specific, likely being a metabolic result of immune system activation, similar to that shown for Juvenile diabetes. In this mini review we point to the benefit of BCG vaccine. We then briefly highlight the pathological involvement of the immune system in the AD both, in the peripheral and the central (brain) compartments. Given the uncertain prophylactic mechanism of the BCG effect against AD we propose to take advantage of the therapeutically planned bladder exposure to BCG. Based on pathological aggregation of wrongly cleaved amyloid precursor protein (APP) resistant to the unfolded protein response (UPR) which results in amyloid beta plaques we predict that BCG may impact the UPR signaling cascade. In addition pathways of innate immunity training concerned with energy metabolism, predict capability of activated immune cells to substitute deranged astrocytes that fail to support neuronal energy metabolism. This mini review points to ways through which immune cells can mediate between BCG vaccination and AD to support the wellness of the central nervous system.

Potential Involvement of Varicella Zoster Virus in Alzheimer's Disease via Reactivation of Quiescent Herpes Simplex Virus Type 1

BACKGROUND

Varicella zoster virus (VZV) has been implicated in Alzheimer's disease (AD), and vaccination against shingles, caused by VZV, has been found to decrease the risk of AD/dementia. VZV might reside latently in brain, and on reactivation might cause direct damage leading to AD, as proposed for herpes simplex virus type 1 (HSV-1), a virus strongly implicated in AD. Alternatively, shingles could induce neuroinflammation and thence, reactivation of HSV-1 in brain.

OBJECTIVE

To investigate these possibilities by comparing the effects of VZV and HSV-1 infection of cultured cells, and the action of VZV infection on cells quiescently infected with HSV-1.

METHODS

We infected human-induced neural stem cell (hiNSC) cultures with HSV-1 and/or VZV and sought the presence of AD-related phenotypes such as amyloid-β (Aβ) and P-tau accumulation, gliosis, and neuroinflammation.

RESULTS

Cells infected with VZV did not show the main AD characteristics, Aβ and P-tau accumulation, which HSV-1 does cause, but did show gliosis and increased levels of pro-inflammatory cytokines, suggesting that VZV's action relating to AD/dementia is indirect. Strikingly, we found that VZV infection of cells quiescently infected with HSV-1 causes reactivation of HSV-1 and consequent AD-like changes, including Aβ and P-tau accumulation.

CONCLUSION

Our results are consistent with the suggestion that shingles causes reactivation of HSV1 in brain and with the protective effects against AD of various vaccines, as well as the decrease in herpes labialis reported after certain types of vaccination. They support an indirect role for VZV in AD/dementia via reactivation of HSV-1 in brain.

Risk of Alzheimer's Disease Following Influenza Vaccination: A Claims-Based Cohort Study Using Propensity Score Matching

Background:

Prior studies have found a reduced risk of dementia of any etiology following influenza vaccination in selected populations, including veterans and patients with serious chronic health conditions. However, the effect of influenza vaccination on Alzheimer’s disease (AD) risk in a general cohort of older US adults has not been characterized.

Objective:

To compare the risk of incident AD between patients with and without prior influenza vaccination in a large US claims database.

Methods:

Deidentified claims data spanning September 1, 2009 through August 31, 2019 were used. Eligible patients were free of dementia during the 6-year look-back period and≥65 years old by the start of follow-up. Propensity-score matching (PSM) was used to create flu-vaccinated and flu-unvaccinated cohorts with similar baseline demographics, medication usage, and comorbidities. Relative risk (RR) and absolute risk reduction (ARR) were estimated to assess the effect of influenza vaccination on AD risk during the 4-year follow-up.

Results:

From the unmatched sample of eligible patients (n = 2,356,479), PSM produced a sample of 935,887 flu–vaccinated-unvaccinated matched pairs. The matched sample was 73.7 (SD, 8.7) years of age and 56.9% female, with median follow-up of 46 (IQR, 29–48) months; 5.1% (n = 47,889) of the flu-vaccinated patients and 8.5% (n = 79,630) of the flu-unvaccinated patients developed AD during follow-up. The RR was 0.60 (95% CI, 0.59–0.61) and ARR was 0.034 (95% CI, 0.033–0.035), corresponding to a number needed to treat of 29.4.

Conclusion:

This study demonstrates that influenza vaccination is associated with reduced AD risk in a nationwide sample of US adults aged 65 and older.

Adult Vaccination as a Protective Factor for Dementia: A Meta-Analysis and Systematic Review of Population-Based Observational Studies

Background

Common vaccinations may have impacts on dementia risk, but current evidence is inconsistent. We therefore investigated the association between vaccinations and dementia risk by systematic review and meta-analysis approach.

Methods

We conducted an extensive search of PubMed, Embase, Cochrane Library, and Web of Science to identify studies that compared the risk of dementia in vaccinated versus unvaccinated populations. The adjusted hazard ratio (HR) and corresponding 95% confidence intervals (CIs) were pooled as measures.

Results

Of the 9124 records initially retrieved, 17 studies with 1857134 participants were included in our analysis. The overall pooled results showed that vaccinations were associated with a 35% lower dementia risk (HR=0.65, 95% CI: 0.60-0.71, Poverall effect < 0.001; I2 = 91.8%, Pheterogeneity<0.001). All types of vaccination were associated with a trend toward reduced dementia risk, with rabies (HR=0.43), tetanus & diphtheria & pertussis (Tdap) (HR=0.69), herpes zoster (HR=0.69), influenza (HR=0.74), hepatitis A (HR=0.78), typhoid (HR=0.80), and hepatitis B (HR=0.82) vaccinations being significant. Individuals with more full vaccination types and more annual influenza vaccinations were less likely to develop dementia. Gender and age had no effect on this association.

Conclusion

Routine adult vaccinations are associated with a significant reduction in dementia risk and may be an effective strategy for dementia prevention. Further research is needed to elucidate the causal effects of this association and the underlying mechanisms.

Evaluation of BCG Vaccination and Plasma Amyloid: A Prospective, Pilot Study with Implications for Alzheimer’s Disease

BCG vaccine has been used for 100 years to prevent tuberculosis. Not all countries, including the United States, adopted the initial World Health Organization recommendation to use BCG. Moreover, many Western countries that had routinely used BCG have discontinued its use. Recent population studies demonstrate lower prevalence of Alzheimer’s disease (AD) in countries with high BCG coverage. Intravesicular instillation of BCG is also used to treat bladder cancer that has not invaded the bladder muscle wall and has been shown to reduce recurrence. Several retrospective studies of bladder cancer patients demonstrated that BCG treatment was associated with a significantly reduced risk of developing AD. Plasma amyloid β assessment has become a fertile area of study for an AD biomarker that is predictive of a positive amyloid PET scan. Mass spectrometry-based plasma amyloid 42/40 ratio has proven to be accurate and robust, and when combined with age and ApoE, is shown to accurately predict current and future brain amyloid status. These parameters, amyloid 42/40 ratio, age and ApoE genotype are incorporated into an Amyloid Probability Score (APS)–a score that identifies low, intermediate or high risk of having a PET scan positive for cerebral amyloid. Community recruitment was used for this open-label pilot study. Forty-nine BCG-naïve, immunocompetent individuals completed our study: prior to BCG prime and boost, as determined by the APS, 34 had low risk (APS 0–35), 5 had intermediate risk (APS 36–57) and 10 had high risk (APS 58–100). The APS range for the participant group was 0 to 94. Follow-up plasma amyloid testing 9 months after vaccination revealed a reduction in the APS in all the risk groups: low risk group (p = 0. 37), intermediate risk group (p = 0.13) and the high-risk group (statistically significant, p = 0.016). Greater benefit was seen in younger participants and those with the highest risk. The small number of participants and the nascent status of plasma amyloid testing will rightfully temper embracement of these results. However, both the favorable direction of change after BCG as well as the utility of the APS—a valuable surrogate AD biomarker—may prompt a definitive large-scale multicenter investigation of BCG and AD risk as determined by plasma amyloid peptide ratios and APS.

Comparison of rates of dementia among older adult recipients of two, one, or no vaccinations

Background

Multiple types of vaccinations are associated with lower risk for dementia, but it is not known if receiving more than one vaccination type is associated with a greater decrease in incident dementia as compared with receiving only one type. We determined if dementia risk is lowest in patients who receive both herpes zoster (HZ) and tetanus, diphtheria, pertussis (Tdap) vaccinations as compared with receipt of only one or the other type of vaccination.

Methods

Primary analysis in a Veterans Health Administration (VA) cohort was replicated in private sector medical claims data. Eligible patients were ≥65 years of age and free of dementia for 2 years prior to baseline (VHA n = 80,070; MarketScan n = 129,200). At index, patients either had both HZ and Tdap, only HZ, only Tdap, or neither vaccination. Confounding was controlled with generalized boosted propensity scores and inverse probability of treatment weighting. Competing risk (VHA) and Cox proportional hazard (MarketScan) models estimated the association between vaccination status and incident dementia.

Results

VHA patients' mean age was 76.8 ± 7.6 years, 4.4% were female and 90.9% were White, and MarketScan patients' mean age was 70.5 ± 5.9 and 65.4% were female. In both cohorts, having both HZ and Tdap vaccinations compared with no vaccination was significantly associated with lower dementia risk (VHA HR = 0.50; 95% CI: 0.43–0.59; MarketScan HR = 0.58; 95% CI: 0.38–0.89). In both cohorts, compared with neither vaccination, patients with only one or the other vaccination types had a significantly lower risk for dementia. Incident dementia was lower in patients with both vaccinations versus only one vaccination type.

Conclusions and Relevance

Receiving two types of vaccinations versus one type was associated with lower dementia risk. Vaccinations may have non‐specific associations with incident dementia. Low cost and accessible, common adult vaccinations may be an overlooked intervention for reducing dementia risk.