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

Depression and Time to Knee Arthroplasty Among Adults Who Have Knee Osteoarthritis

BACKGROUND

Depression is common in osteoarthritis (OA) and is associated with poor outcomes following total knee arthroplasty (TKA). Depression can increase pain sensitivity and may be related to an increased likelihood of TKA.

METHODS

Nationally distributed electronic health record data from 2010 to 2018 were used to identify eligible patients (n = 9,466) who had knee OA and were 45 to 80 years of age. Cox proportional hazard models were computed to estimate the association between depression and incident TKA for all patients and by age group (45 to 54, 55 to 64, and 65 to 80 years of age). Confounding was controlled using entropy balancing. Sensitivity analyses determined if the association between depression and TKA differed when depression occurred in the 12 months occurring 90, 60, 30, and 0 days lag time before TKA.

RESULTS

The mean age of the sample was 63 (range, 45 to 80), 64.0% were women, 83.3% were White race, and approximately 50% resided in the Midwest. There was no association between depression and incident TKA (hazard ratio = 0.97; confidence interval = 0.81 to 1.16]). Results did not differ in age-stratified analyses. Sensitivity analyses revealed a higher percentage of TKA among depressed versus nondepressed patients (24.2 versus 21.6%; P = .028) when the patient's depression diagnosis was established in the 12 months with no lag time before TKA.

CONCLUSIONS

Patients who have knee OA and comorbid depression, compared to those who have only knee OA, do not have an increased likelihood of TKA. The multifactorial, complex decision to obtain TKA does not appear to be influenced by depression, but depression is a common comorbidity.

Do microbes play a role in Alzheimer's disease?

Alzheimer's disease is a complex and progressive condition that affects essential neurological functions such as memory and reasoning. In the brain, neuronal loss, synaptic dysfunction, proteinopathy, neurofibrillary tangles, and neuroinflammation are the hallmarks of Alzheimer's disease pathophysiology. In addition, recent evidence has highlighted that microbes, whether commensal or pathogenic, also have the ability to interact with their host and to regulate its immune system, therefore participating in the exchanges that lead to peripheral inflammation and neuropathology. Because of this intimate relationship, bacteria, viruses, fungi, and protozoa have been implicated in the development of Alzheimer's disease. Here, we bring together current and most recent evidence of the role of microbes in Alzheimer's disease, raising burning questions that need to be addressed to guide therapeutic approaches and potential prophylactic strategies.

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.

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.

Alzheimer's disease as a viral disease: Revisiting the infectious hypothesis

Alzheimer's disease (AD) represents the most frequent type of dementia in elderly people. Two major forms of the disease exist: sporadic - the causes of which have not yet been fully understood - and familial - inherited within families from generation to generation, with a clear autosomal dominant transmission of mutations in Presenilin 1 (PSEN1), 2 (PSEN2) or Amyloid Precursors Protein (APP) genes. The main hallmark of AD consists of extracellular deposits of amyloid-beta (Aβ) peptide and intracellular deposits of the hyperphosphorylated form of the tau protein. An ever-growing body of research supports the viral infectious hypothesis of sporadic forms of AD. In particular, it has been shown that several herpes viruses (i.e., HHV-1, HHV-2, HHV-3 or varicella zoster virus, HHV-4 or Epstein Barr virus, HHV-5 or cytomegalovirus, HHV-6A and B, HHV-7), flaviviruses (i.e., Zika virus, Dengue fever virus, Japanese encephalitis virus) as well as Human Immunodeficiency Virus (HIV), hepatitis viruses (HAV, HBV, HCV, HDV, HEV), SARS-CoV2, Ljungan virus (LV), Influenza A virus and Borna disease virus, could increase the risk of AD. Here, we summarized and discussed these results. Based on these findings, significant issues for future studies are also put forward.

Lower risk for COVID-19 hospitalization among patients in the United States with past vaccinations for herpes zoster and tetanus, diphtheria and pertussis

Influenza, tetanus, diphtheria, and herpes zoster (HZ) vaccination received within 10 years of the COVID-19 pandemic have been associated with less severe COVID-19 infection. We expanded on this evidence to determine if a receiving two different vaccinations (i.e., HZ and tetanus, diphtheria, and pertussis (Tdap)) was associated with a lower risk for COVID-19 hospitalization. De-identified medical record data from a large mid-western health care system was used to determine if, compared to those with neither HZ or Tdap vaccination, patients with either HZ or Tdap and patients with both HZ and Tdap vaccination had lower risk for COVID-19 hospitalization between 4/1/2020 and 12/31/2020. Confounding was controlled using entropy balancing. Patients (n = 363,293) were 71.5 (±8.4) years of age, 57.8% female and 89.2% White race. Prior to controlling for confounding, as compared to patients without either vaccination, those that had either HZ or Tdap were significantly less likely to have a COVID-19 hospitalization (RR = 0.85; 95 %CI: 0.75-0.95). The risk for hospitalization decreased further among those with both HZ and Tdap vaccination (RR = 0.45; 95 %CI:0.28-0.71). After controlling for confounding, including healthy patient bias, receiving both vs. neither vaccinations remained significantly associated with a lower risk of COVID-19 hospitalization (RR = 0.48; 95 %CI: 0.26-0.90). Receiving both Tdap and HZ vaccination is associated with lower risk for COVID-19 hospitalization. Whether there is any benefit of past vaccination exposure in COVID-19 vaccinated patients should be investigated.

The association of microbial infection and adaptive immune cell activation in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the most common form of dementia. Early symptoms include the loss of memory and mild cognitive ability; however, as the disease progresses, these symptoms can present with increased severity manifesting as mood and behaviour changes, disorientation, and a loss of motor/body control. AD is one of the leading causes of death in the UK, and with an ever-increasing ageing society, patient numbers are predicted to rise posing a significant global health emergency. AD is a complex neurophysiological disorder where pathology is characterized by the deposition and aggregation of misfolded amyloid-beta (Aβ)-protein that in-turn promotes excessive tau-protein production which together drives neuronal cell dysfunction, neuroinflammation, and neurodegeneration. It is widely accepted that AD is driven by a combination of both genetic and immunological processes with recent data suggesting that adaptive immune cell activity within the parenchyma occurs throughout disease. The mechanisms behind these observations remain unclear but suggest that manipulating the adaptive immune response during AD may be an effective therapeutic strategy. Using immunotherapy for AD treatment is not a new concept as the only two approved treatments for AD use antibody-based approaches to target Aβ. However, these have been shown to only temporarily ease symptoms or slow progression highlighting the urgent need for newer treatments. This review discusses the role of the adaptive immune system during AD, how microbial infections may be contributing to inflammatory immune activity and suggests how adaptive immune processes can pose as therapeutic targets for this devastating disease.

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.

Causal evidence that herpes zoster vaccination prevents a proportion of dementia cases

The root causes of dementia are still largely unclear, and the medical community lacks highly effective preventive and therapeutic pharmaceutical agents for dementia despite large investments into their development. There is growing interest in the question if infectious agents play a role in the development of dementia, with herpesviruses attracting particular attention. To provide causal as opposed to merely correlational evidence on this question, we take advantage of the fact that in Wales eligibility for the herpes zoster vaccine (Zostavax) for shingles prevention was determined based on an individual's exact date of birth. Those born before September 2 1933 were ineligible and remained ineligible for life, while those born on or after September 2 1933 were eligible to receive the vaccine. By using country-wide data on all vaccinations received, primary and secondary care encounters, death certificates, and patients' date of birth in weeks, we first show that the percentage of adults who received the vaccine increased from 0.01% among patients who were merely one week too old to be eligible, to 47.2% among those who were just one week younger. Apart from this large difference in the probability of ever receiving the herpes zoster vaccine, there is no plausible reason why those born just one week prior to September 2 1933 should differ systematically from those born one week later. We demonstrate this empirically by showing that there were no systematic differences (e.g., in pre-existing conditions or uptake of other preventive interventions) between adults across the date-of-birth eligibility cutoff, and that there were no other interventions that used the exact same date-of-birth eligibility cutoff as was used for the herpes zoster vaccine program. This unique natural randomization, thus, allows for robust causal, rather than correlational, effect estimation. We first replicate the vaccine's known effect from clinical trials of reducing the occurrence of shingles. We then show that receiving the herpes zoster vaccine reduced the probability of a new dementia diagnosis over a follow-up period of seven years by 3.5 percentage points (95% CI: 0.6 - 7.1, p=0.019), corresponding to a 19.9% relative reduction in the occurrence of dementia. Besides preventing shingles and dementia, the herpes zoster vaccine had no effects on any other common causes of morbidity and mortality. In exploratory analyses, we find that the protective effects from the vaccine for dementia are far stronger among women than men. Randomized trials are needed to determine the optimal population groups and time interval for administration of the herpes zoster vaccine to prevent or delay dementia, as well as to quantify the magnitude of the causal effect when more precise measures of cognition are used. Our findings strongly suggest an important role of the varicella zoster virus in the etiology of dementia.

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.

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.

BCG Vaccine—The Road Not Taken

The Bacillus Calmette-Guérin (BCG) vaccine has been used for over one hundred years to protect against the most lethal infectious agent in human history, tuberculosis. Over four billion BCG doses have been given and, worldwide, most newborns receive BCG. A few countries, including the United States, did not adopt the WHO recommendation for routine use of BCG. Moreover, within the past several decades, most of Western Europe and Australia, having originally employed routine BCG, have discontinued its use. This review article articulates the impacts of those decisions. The suggested consequences include increased tuberculosis, increased infections caused by non-tuberculous mycobacteria (NTM), increased autoimmune disease (autoimmune diabetes and multiple sclerosis) and increased neurodegenerative disease (Parkinson’s disease and Alzheimer’s disease). This review also offers an emerged zoonotic pathogen, Mycobacteriumavium ss. paratuberculosis (MAP), as a mostly unrecognized NTM that may have a causal role in some, if not all, of these diseases. Current clinical trials with BCG for varied infectious, autoimmune and neurodegenerative diseases have brought this century-old vaccine to the fore due to its presumed immuno-modulating capacity. With its historic success and strong safety profile, the new and novel applications for BCG may lead to its universal use–putting the Western World back onto the road not taken.

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.

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.