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Chapter 1: What is the main topic discussed in this episode?
Hey, it's Laura Lichtman, and you're listening to Science Friday. The benefits of getting a vaccine seem relatively straightforward. Like, you get the shingles vaccine, it protects you from shingles. But there may be more to the story. For example, researchers have found a surprising link between getting the shingles vaccine and a lower risk of developing dementia.
And that's not the only vaccine that seems to boost health in unexpected ways. So what's going on here?
Chapter 2: What are the benefits of the shingles vaccine beyond preventing shingles?
Here to get into the details are my guests. Dr. Pascal Geldsetzer is an epidemiologist at Stanford University who's studying the association between the shingles vaccine and lower rates of dementia. And Dr. Helen Chu is a physician and epidemiologist at the University of Washington who studies flu, RSV and COVID-19. Helen, Pascal, welcome to Science Friday.
Thank you so much for having me.
Thanks for having us.
Thanks for being here. Helen, start by orienting us. Give me some examples of some of the unintended benefits of vaccines, you know, beyond preventing the specific disease they were designed for.
We think of vaccines as preventing the disease that we're vaccinating against, flu or RSV or COVID.
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Chapter 3: How is the shingles vaccine linked to a lower risk of dementia?
But oftentimes, these vaccines can have other effects, like preventing heart attacks or strokes. There are a couple of reasons why we think this happens. The first is perhaps we are not measuring the infections when they occur. So very well may be that somebody comes in with a heart attack, and the trigger for that heart attack was a flu infection, but we never captured that flu infection.
And so when we look at this on a population level in studies, what we can see is that flu vaccines actually prevent heart attacks.
Can I just dig in here for a second? So the idea is that flu could actually trigger a heart attack or a heart health problem. And so if you're preventing the flu, you're you're preventing this downstream effect of having that infection.
That's correct. It could be preventing that. And it's possible that the flu infection is triggering inflammation in your blood vessels. And that inflammation is what's causing the heart attack or the stroke. We think that's what's happening. And we're not able to measure that in the way we normally do these studies.
Okay, so that's one potential reason you see these downstream effects. Is there another?
I think the main point is that either we're not measuring it or these things are happening well after the infection is being diagnosed. And so it could be that you could have a heart attack at the time of your hospitalization for flu, but we never captured that flu infection. The other way that it could happen is that that heart attack or stroke happened a few weeks to months later.
And we're not capturing it because it wasn't at the time of the immediate infection, but that infection triggered this cascade of inflammation that later on led to all of these other adverse events like strokes or heart attacks.
Gotcha. OK, I want to dig into a case study for a couple minutes and then we'll zoom back out. But, Pascal, let's talk about this relationship between the shingles vaccine and dementia. You looked into this. Why did you start investigating this in the first place?
Well, I think the shingles vaccination program, as it was rolled out in several countries, provides this really unique opportunity in observational data to get at cause and effect rather than just correlation, right? We usually always have this fundamental problem in cohort studies, in electronic health record data, medical claims data.
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Chapter 4: What unintended benefits do vaccines provide beyond their intended purpose?
In fact, comparison groups that are very similar to what we would have in a clinical trial, which is the gold standard, right, to get at cause and effect. So they said in a number of countries, so for example, in the UK, if you had your 80th birthday just prior to the start date of the shingles vaccination program, you were ineligible and you remained ineligible for life.
Well, if you had it just after, you were eligible. And so now we can compare in our data people whose only difference is a week or so in age and But they have this massive difference in ever getting the vaccine because of this eligibility rule at a pretty arbitrary date of birth eligibility cutoff.
And now you've got comparison groups just like in a clinical trial where we know that all that's different about the control group and the intervention group is whether the coin landed on heads or tails. Here, all that's different about the intervention and the control group is whether you happen to be born just a few days earlier or a few days later. essentially by random chance.
So this is what makes this evidence that we're able to generate for shingles vaccination and its health outcomes so much more powerful and so unique. You know, such a unique opportunity opportunity in observational data to get a cause and effect is really rare.
And that's why I'm so excited about this, the shingles vaccination program and research and, you know, especially these large effects that we keep seeing for dementia.
Yeah, so what did you find?
Yeah, so we see these large protective effects for new diagnoses of dementia in the future. And we keep seeing this in various different, in all these different settings that have rolled out the Shingles vaccine using these state-of-birth cutoffs. So it's not a fluke finding. It's something that repeats in data set after data set.
And there are large protective effects, which, you know, would be... How large? So our best guess is a 20% reduction in new dementia diagnoses over seven years. So that is large, especially given that it's such a simple, inexpensive, readily available, one-off intervention, right?
It's not even a medication that you have to take every day, let alone a lifestyle regimen that you have to adhere to over decades, right? And it's safe and prevents shingles as well, which is nice. And so you've got a readily scalable intervention with large protective effects. So that would be a big, big deal for population health.
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