Does the shingles vaccine reduce the risk of dementia? What research has shown

I read that the shingles vaccine might protect against dementia. Is that true? Should I get it?

It's not a rumour. It's one of the most interesting lines of research in recent years, and it deserves an honest answer — which includes stating what is still unknown.

What studies have found

As of 2024, several independent groups have published results that point in the same direction: those who received the vaccine against herpes zoster (shingles) have fewer dementia diagnoses in the following years. The papers were published in top-tier journals — Nature, Nature Medicine, The Lancet Neurology, Cell — and the numbers speak of reductions in the order of one-fifth of cases, or several months gained without a diagnosis.

Why this evidence is stronger than usual

Here's the part that makes a difference. The usual problem with this type of study is that those who get vaccinated tend to be those who take better care of their health — and then it's never clear whether the credit goes to the vaccine or to other factors. These studies circumvented this by using natural experiments: countries where vaccination was made available from a certain birth date, creating two groups that were practically identical in everything, separated only by having been born a few weeks earlier or later. Those who were left out were not less careful — they were just less lucky with their birth date.

This design is much closer to a cause-and-effect relationship than a common observational study. And it has been replicated in different countries, by different teams, with consistent results.

What is still unknown

We don't know why. There are two main hypotheses: the shingles virus, which lies dormant in the body after chickenpox, can cause inflammation and damage to brain vessels when it reactivates — and the vaccine would prevent this; or the vaccine itself may have a more general effect on the immune system. It has not yet been decided.

And, above all: this is not yet an official recommendation to prevent dementia. The World Health Organisation's guidelines on dementia risk reduction do not include vaccination against shingles. The vaccine is recommended for what it was made for — to prevent shingles and the neuralgia that follows, which is painful and can last for months. If there is a benefit for the brain, it is an extra that research is still confirming.

In Portugal

The Shingrix vaccine has been approved by Infarmed since 2022, but it is not part of the National Vaccination Plan and is not subsidised — it is paid in full by those who take it, which makes it inaccessible to many people. The Portuguese Society of Internal Medicine and the Portuguese Association of General and Family Medicine have published a consensus document with recommendations on who benefits from vaccination, and there is ongoing discussion about its inclusion in the National Plan.

What to do

Talk to your GP. The decision should be based on the risk of getting shingles — which increases with age and low immunity — and not on the hope of preventing dementia, which is a possibility that science is still confirming. If you decide to take it, take it for the reasons that are already established; if the benefit for the brain is confirmed, it will have been a good deal.