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Journalism of Courage
A large “natural experiment” from Wales has been able to confirm what health records had previously suggested — getting vaccinated against the viral infection shingles reduces the odds of a person getting dementia. The study — based on the data of 2,80,000 older individuals — found that people who had been vaccinated were 20 per cent less likely to develop dementia.
The study found that dementia diagnosis in the people, who had received the shingles vaccine, reduced 3.5 percentage points over a seven-year period — this is equal to a 20 per cent lower relative risk of getting dementia as compared to the unvaccinated population. The researchers also found that the effect was more pronounced in women rather than men.
The study has been termed a “natural experiment” because of the way the vaccine was rolled out in Wales. The vaccination programme started on September 1, 2013. Anyone who was 79 on that date became eligible for vaccination for a year. Those who were 78 became eligible the year after. However, anyone over the age of 80 years on the date was out of luck and was not eligible for vaccination. This created a natural cohort of people of similar age, living in similar conditions, half of whom were eligible and half ineligible to receive the vaccine. This created a natural randomised control trial for researchers at Stanford Medicine to study the impact of the vaccine on dementia.
So far, all evidence of the phenomenon had been from patient records, which had one major bias — people who were vaccinated took better care of their health. “All these associational studies suffer from the basic problem that people who get vaccinated have different health behaviours than those who don’t. In general, they’re seen as not being solid enough evidence to make any recommendations on,” said Dr Pascal Geldsetzer, the corresponding author of the study and assistant professor of medicine at the division of primary care and population health at Stanford University.
While the present study looks at the impact of a live-attenuated shingles vaccine Zostavax used in the vaccination programme — which was discontinued in 2020 — another study last year by Oxford university shows that the new vaccine may offer a stronger protection still.
The Oxford study based on the health records of 200,000 people from the US, found a 17 per cent reduction in dementia diagnoses in the six years following immunisation with a recombinant vaccine called Shingrix. This equated to people living an additional 164 days or more without dementia.
The scientists do not yet know for sure why this happens. One theory is that it prevents the reactivation of the virus, which has been linked to long-lasting cognitive impact by affecting the blood vessels of the brain that can in turn cause stroke or bleeding. The researchers also say that it may be possible that the vaccine leads to changes in the immune system that may protect against dementia.
Shingles typically causes a band of extremely painful rashes, caused by the same varicella-zoster virus that leads to chicken pox. After the virus causes chickenpox in childhood, it remains sleeping in the nerve cells for life. It may, however, reactivate later in life when a person’s immune system is weakened.
