Can a shot in the arm help to avoid dementia?

Of all the ways we’ve heard of to reduce the risk of dementia, here’s one that that hasn’t received much publicity — until now.

Recently published Welsh and American research concluded that shingles vaccines might play a useful role.

If you’ve had a shingles vaccination you’ll know that the current version is Shingrix, which replaced Zostavax.

They’re different types of vaccines. Zostavax was made using a weak version of the live virus, which made it unsuitable for anyone with compromised immunity.

Shingrix has been shown to be both more effective at preventing shingles and suitable for immune-compromised people.

Shingles might be more prevalent than we realise. Statistically, if we all live to be 85, half of us will have had it. And if you’ve had it you’ll know it produces a painful rash with a band of blisters on one side of the face or body. It’s the reactivation of the chickenpox virus.

As we get older we’re more at risk of complications that can include long-term pain, neurological issues, vision problems if it affects the eye area, skin infections, and even pneumonia or encephalitis (inflammation in the brain).

So it goes without saying that none of us wants shingles or any of the nasty complications.

Shingrix is free to people over 65, to Aboriginal or Torres Strait Islander people over 50, and to anyone over 18 who has an immune condition that makes them eligible for the vaccine.

But back to the research. In Wales this involved Zostavax which was introduced there in September 2013.

It was deemed that adults born on or after September 2, 1933 were eligible for it and those born before that date were not. So if you’d already turned 80 by then you missed out.

Researchers saw this as an opportunity to set up a ‘natural experiment’ comparing the two groups. Since some scientists had begun proposing a link between shingles and dementia, this seemed like a smart way to test it.

They focused on comparing people born on or shortly after 2 September 1933 with those born shortly before that date. People born only a few weeks apart presumably won’t vary much from each other in a systematic way.

The only obvious difference was that around 47% of those born on or just after the eligibility date got vaccinated for shingles within 12 months of the start of the program.

The researchers monitored the electronic health records of the two groups (around 280,000 people in total) for seven years (i.e. until late 2020).

In that time the vaccinated group showed 3.5% less probability of being diagnosed with dementia, but interestingly, only in women.

This doesn’t sound like much of a reduction, but using stats the way researchers can, they argued that the vaccine reduced the probability of a dementia diagnosis by one-fifth over seven years.

Zostavax was also rolled out in England to a much larger population, and over a nine-year follow-up showed a similar result.

But Zostavax was discontinued. So what about Shingrix?

In the US that switch happened in October 2017. Using a similar idea to the Welsh, American researchers were keen to compare the incidence of dementia among people who received Zostavax just before it was phased out with those who got the new Shingrix vaccine.

They compared 103, 837 people who had their first dose of Zostavax between late 2014 and late 2017 with the same number who’d had their first dose of Shingrix between late 2017 and late 2020. (Both vaccines require two doses 2-6 months apart, but people with compromised immunity are recommended to have 1-2 months between doses.)

Over a six-year follow-up they found a protective effect in both men and women, though more so in women, and concluded that compared to Zostavax, Shingrix provided a 17% increase in the time lived without a dementia diagnosis (which might suggest that a vaccine does more delaying than outright preventing).

A obvious question is how a shingles vaccine does this (given those for e.g. flu, tetanus, whooping cough and diphtheria apparently don’t).

One reason is that shingles generates inflammation, and inflammation can contribute to dementia. So not getting shingles is a plus.

Another reason is that the vaccine stimulates the immune system. Since there are immunological differences between men and women, this might explain why both vaccines seem to be more effective in women — a bonus, given women have around twice as much dementia as men.

This kind of research is hardly watertight though. It shows an association between more vaccination and less dementia but can’t prove that one caused the other.

Still, three studies showing the same trend does start to look convincing.

And even if future research fails to support the dementia finding, the chance to avoid the worst of shingles still makes a couple of Shingrix shots worthwhile.

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