The effect of herpes zoster vaccines on incident dementia in England: Protocol for an OpenSAFELY regression discontinuity study
This paper outlines a protocol for an OpenSAFELY regression discontinuity study designed to evaluate the impact of England's herpes zoster vaccination program, which transitioned from Zostavax to Shingrix, on the incidence of dementia using linked electronic health records.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
Dementia is a condition that slowly erodes memory and thinking, casting a long shadow over the lives of millions of older adults and their families. While researchers have spent decades searching for ways to slow or prevent this decline, the focus has often been on lifestyle changes or specific medications. However, a growing body of science suggests that the immune system plays a crucial role in brain health. One specific virus, known as the shingles virus, lies dormant in the body after a person recovers from chickenpox. Years later, it can reactivate, causing a painful rash and nerve damage. Beyond the immediate pain, there is a lingering question: could this viral reactivation, or the body's fight against it, trigger changes in the brain that lead to dementia? If the answer is yes, then a simple vaccine might do more than just prevent a rash; it could potentially protect the mind.
In England, a national program was launched to vaccinate older adults against shingles, first with a live vaccine called Zostavax and later with a newer, non-live vaccine called Shingrix. Because the government offered these vaccines based strictly on a person's birth date, researchers have identified a unique opportunity to study their long-term effects. They have noted that people born just before a specific cutoff date were not offered the vaccine, while those born just after were. This creates a natural experiment where two groups of people, who are nearly identical in age and background, differ only in their access to the vaccine. By comparing these two groups, scientists aim to isolate the effect of the vaccine itself, much like seeing if a specific treatment works by comparing two nearly identical twins where only one receives the medicine.
A team of researchers led by Venexia Walker and colleagues at the University of Bristol and the University of Oxford has designed a study to investigate this very question using a massive database of English health records called OpenSAFELY. Their goal is to determine whether receiving the shingles vaccine reduces the likelihood of developing dementia. The study focuses on two distinct moments in time. The first looks at the introduction of the Zostavax vaccine in September 2013, which was offered to people who turned 79 that year. The second examines the switch to the Shingrix vaccine in September 2023, which became available to people turning 65. By analyzing the medical histories of millions of people, the researchers plan to see if the group that received the vaccine develops dementia at a lower rate than the group that did not.
The researchers are not guessing; they are using a rigorous method called regression discontinuity. This approach relies on the fact that the vaccine eligibility rules were sharp and clear. For the first part of the study, they will look at people born in the months immediately before and after the cutoff date in 2013. Since these individuals are so close in age, their health histories, lifestyles, and risks for dementia should be almost the same, except for the vaccine. If the vaccinated group shows significantly fewer cases of dementia, it will suggest the vaccine is the cause of that difference. The team will also look at the newer Shingrix program, which targets people at age 65, to see if the benefits hold true for a different generation and a different type of vaccine.
This study is a protocol, which means it is a detailed plan for research that has not yet been completed. The authors have laid out exactly how they will gather data, who they will include, and how they will analyze the results. They plan to use records from general practitioners, hospital admissions, and death certificates to track who gets vaccinated and who develops dementia. They are careful to exclude people who already had dementia before the study began or those who were too sick to receive a live vaccine. They will also check to ensure that the two groups being compared are truly similar in every way except for the vaccine, looking at factors like smoking, other health conditions, and where people live.
The researchers are proceeding with caution and precision. They acknowledge that dementia is a complex disease that develops over many years, and the date a doctor records a diagnosis might not be the exact moment the disease started. They also note that their findings will apply most directly to people near the age cutoffs they are studying, rather than to everyone in the population. However, by using such a large and diverse dataset, they hope to provide clear evidence on whether protecting the body from the shingles virus also protects the brain. If the results show a reduction in dementia, it would be a powerful discovery, suggesting that a routine vaccination could be a simple, effective tool in the fight against cognitive decline. For now, the scientific community waits for the data to be analyzed, hoping that this careful, methodical work will reveal a new path toward preserving memory and quality of life for older adults.
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