Shingles vaccine & lower dementia risk: what new study says

What is shingles?

Shingles is a viral infection that causes painful rashes. While shingles can occur anywhere on the body, it typically looks like a single stripe of blisters that wraps around the left or right side of the torso, along the path of the nerve from which the virus spreads.

It is caused by the varicella-zoster virus — the virus which also causes chickenpox. After a bout of chickenpox, usually during childhood, the virus remains dormant in one’s nerve cells for life. It can reactivate and cause shingles when a person’s immune system is weakened.

People who have never had chickenpox may get the infection if they come in direct contact with the fluid released by the shingles rashes, or breathe in the virus particles.

Pain can persist even after rashes go away. In severe cases, the rashes cause vision loss if they are close to the eye, facial paralysis, or inflammation of the brain.

The shingles vaccine, which prevents the reactivation of the varicella-zoster virus, is recommended primarily to individuals over the age of 50 years. It may also be recommended to adults living with a weakened immune system due to conditions such as HIV.

What did the Welsh study find? Why is it unique?

Previous studies shown an association between shingles vaccination and lower risk of dementia. But most of the evidence has come from patient records, which are subject to one major bias: people who are vaccinated tend to take better care of their health.

The unique roll-out strategy of the shingles vaccine in Wales created a “natural experiment” that effectively mimicked a randomised control trial, the most credible level of evidence in medical research, much better than patient records.

The programme, which began on September 1, 2013, allowed anyone who was between 79- and 80-years-old on that date to get the shingles vaccine over the next year. While 78-year-olds could receive the vaccine the year after, those above the age of 80 would never be eligible. This created a natural cohort of people — of similar age and living in similar conditions —  only half of whom were eligible to receive the shingles vaccine.

Upon analysing the health outcomes of this cohort, the Welsh study published in Nature last month found that dementia diagnoses among people who had gotten the shingles vaccine reduced 3.5 percentage points over a seven-year period. This equates to a 20% lower relative risk of getting dementia compared to the unvaccinated population.

Scientists are yet to determine what might be behind this. One theory looks at the shingles-causing virus which has been linked to long-lasting cognitive effects. Preventing its reactivation through vaccination, could directly reduce the risk of dementia. Some researchers have also pointed to changes in the immune system brought about by the shingles virus which could protect against dementia.

Do both shingles vaccines have a similar protective effect?

There are two approved shingles vaccines — both of which are available in India for a price of Rs 6,000 to Rs 17,000 per dose. Zostavax uses a live, weakened virus, while Shingrix uses a recombinant technology to develop parts of the virus that do not cause the disease.

The Welsh study was based on people who had received the older Zostavax vaccine. However, a study from Oxford University last year showed that the new recombinant vaccine may also offer protection against dementia. The study, based on the health records of 200,000 persons in the US, found a 17% reduction in dementia diagnoses in the six years following immunisation with Shingrix.

Note that there is also some evidence linking lower dementia risk with other common vaccines. Published in Alzheimer’s & Dementia, a recent study covering 130 million people found a correlation between a lower risk of dementia and the hepatitis A, typhoid and diphtheria vaccines.

Another 2023 study in the Journal of Alzheimer’s Disease found the diphtheria, pneumococcal and shingles vaccine to be associated with a 30%, 27%, and 25% reduction in the risk of dementia.