A new study to drive the point home? New work published in the journal Nature largely support the theory of a double protective effect of the shingles vaccine: it would, of course, offer protection against shingles but would also reduce the risk of dementia. previous works Similar studies have been published in the past. The bias is that those who choose to get vaccinated also have better health habits than those who don't. This time, the work carried out by Stanford University (USA) – conducted on the Welsh population – does not appear to be biased.
Shingles is a viral infection that causes a painful rash. It is caused by the same virus that causes chickenpox: the varicella-zoster virus (VZV). After contracting chickenpox, usually during childhood, the virus remains latent in nerve cells for life. In older people or those with weakened immune systems, the latent virus can reactivate later in life and cause shingles. Although often mild, it can have serious consequences in immunocompromised people, such as hearing loss or paralysis. In France, for example, this vaccine is recommended for all adults aged 65 and over, as well as for people aged 18 and over with weakened immune systems.
20% lower risk of dementia
This new research was based on a vaccination program for seniors that began on September 1, 2013, in Wales. Anyone aged 79 at that time was eligible for the vaccine for one year. Those aged 78 would have access the following year, and so on. However, those already aged 80 could no longer benefit from the vaccine. The researchers were therefore able to compare a population of almost the same age, vaccinated or not, using the eligibility threshold as the sole criterion.
By comparing people who turned 80 just before September 1, 2013, to those who turned 80 just after, the researchers were able to isolate the effect of vaccine eligibility. We know that if we randomly take a thousand people born one week and a thousand people born a week later, there should be no difference on average.", explains to Science and Future THE Dr. Pascal Geldsetzer, assistant professor of medicine at Stanford and lead author of the study. "[The two groups] are similar, except for this tiny age difference." Conditions " as close as possible » of a randomized controlled trial.
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In total, more than 280,000 people aged 71 to 88 were eligible for inclusion in the study. However, only those around 80 years old, close to the eligibility threshold, were examined. By 2020, seven years after the study began, approximately 1 in 8 adults aged 86 to 87 had been diagnosed with dementia. However, among those vaccinated against shingles, this risk was reduced by approximately 20% compared to unvaccinated individuals.
The research also showed that protection against dementia was stronger in women than in men. This may be due to a difference in the immune response between men and women. Or a difference in how dementia develops. Women generally have a higher antibody response after vaccination. We also know that both shingles and dementia are more common in women than in men.“, supposes Dr. Geldsetzer.
A poorly understood mechanism
But how is it possible that a vaccine against the varicella-zoster virus could have an effect on dementia? Two mechanisms could be at play, one not excluding the other. The first mechanism is specific to the varicella virus“, explains the researcher. “There is a growing body of research showing that viruses that preferentially target the nervous system and hibernate there for much of their lives may be involved in the development of dementia. One such virus, of course, is chickenpox, which can cause shingles later in life. The second mechanism is potentially independent of the chickenpox virus. There is growing evidence that vaccines can have effects on the immune system beyond simply producing the specific antibodies they were designed to produce, and that these broader immunological effects may have beneficial effects on other diseases.”. »
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The question remains how long the vaccine protects against dementia. Since the chickenpox and shingles vaccines target the same virus, will younger generations who received a chickenpox vaccine also be protected later in life? I think these research questions remain open. If the mechanism linking shingles vaccination to dementia is through the chickenpox virus-specific mechanism I described just before, then it seems plausible that future generations who received the chickenpox vaccine as children will have a lower incidence of dementia.", assumes Dr. Geldsetzer. In the meantime, the team hopes to be able to launch a classic clinical trial soon, in order to definitively conclude on a cause-and-effect link.
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