As I mentioned in a previous article here, it is clear that some chronic diseases are at least in part caused by infectious agents such as viruses or bacteria1. One major group of chronic diseases in the modern world is that of dementia. There are numerous types, with three of the most common being Alzheimer’s disease, vascular dementia and chronic traumatic encephalopathy (CTE)2.
Alzheimer’s disease is the most common form of dementia and results in impaired memory, thinking and behaviour. It disrupts the brain’s neurons, affecting how they function and communicate with each other. Some people contract Alzheimer’s disease due to a genetic mutation, but most of those who come down with the disease have no known cause3.
Vascular dementia is a form of dementia caused by brain damage resulting from restricted blood flow in the brain. It affects reasoning, planning, judgement and attention. It can be cause by strokes, untreated high blood pressure or diabetes causing vascular disease in the small blood vessels deep within the brain4.
CTE is a type of dementia caused by many repeated head injuries, and can affect brain function over time, enough to interfere with the person’s normal or working life. Repeated head injuries can take the form of concussion, or even smaller head knocks without symptoms, which are referred to as subconcussion5.
The causes of Alzheimer’s disease are, as mentioned above, largely unclear and there are currently no particularly effective preventative measures.
A recent paper by researchers from Stanford University and the University of Vienna attempted to try to find some evidence of causality, and took advantage of the fact that in Wales, eligibility for the herpes zoster vaccine (Zostavax) for the prevention of shingles was determined based on an individual’s exact date of birth. Those born before September 2nd, 1933 were ineligible and remained ineligible for life, while those born on or after September 2nd, 1933 were eligible to receive the vaccine6.
By using country-wide data on all vaccinations received, primary and secondary care encounters, death certificates, and patients’ date of birth in weeks, the authors showed 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 2nd, 1933 should differ systematically from those born one week later. They demonstrated this empirically by showing that there were no systematic differences (e.g., in pre-existing conditions or uptake of other preventative interventions) between adults across the date-of-birth eligibility cutoff, and that there were no other interventions that used the same date-of-birth eligibility cutoff as used for the herpes zoster vaccine program6.
They argue that this natural randomisation trial, indicates a robust causal effect estimate. They 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, and that the protective effects from the vaccine for dementia are far stronger among women than men. They therefore conclude that “there is a significant role for the Varicella zoster virus in the causes of dementia”6.
The list of chronic diseases associated with long-term viral infections is growing, and now includes several cancers, some diabetes, atherosclerosis, multiple sclerosis and some forms of dementia. It will likely continue to grow, and to indicate this, there are several review papers in the scientific literature listing such connections. Although the paper6 under discussion has not yet been peer-reviewed, avoiding the painful occurrence of shingles is reason enough to get the vaccine. So, do yourself a favour, get your shingles vaccine! The benefits may be more than you know.
Sources
- https://blotreport.com/2023/12/03/the-kissing-disease-and-multiple-sclerosis/
- https://www.dementia.org.au/information/about-dementia/types-of-dementia
- https://www.dementia.org.au/about-dementia/types-of-dementia/alzheimers-disease
- https://www.dementia.org.au/about-dementia/types-of-dementia/vascular-dementia
- https://www.dementia.org.au/about-dementia/types-of-dementia/chronic-traumatic-encephalopathy-dementia
- https://www.medrxiv.org/content/10.1101/2023.05.23.23290253v1
