Shingles vaccine reduces risk of dementia

Scientists who have been tracking cases of dementia in Welsh adults have uncovered strong evidence that having the shingles vaccine - which blocks the chicken pox virus from periodically returning as an excruciatingly painful blistering rash, which is much more common as we get older - also significantly reduces the risk of developing Alzheimer’s Disease. The study relied on the fact that, in 2013, shingles vaccination began to be offered routinely to adults who were over 70 but under 80. And this meant that there were some people who were nearly identical in age and most other risk factors, but differed only in terms of whether they got the jab. This was an ideal random sample, which ultimately showed that people who received Zostavax were up to 20% less likely to be diagnosed with dementia in the seven year follow up period than those who didn’t have the jab. Pascal Geldsetzer at Stanford University carried out the research…

Pascal - What we want to show that a new vaccine or new medication works is a randomised clinical trial. So we may take say a thousand study participants and throw a coin and assign them that way to a vaccine group or no vaccine group. And the power of this is that we know these are really good comparison groups because all that's different for them is whether the coin landed on heads or tails. In the case of Wales we have a very similar situation in the way in which they wrote out the shingles vaccine program. So specifically they said if you had your 80th birthday just prior to the start date of the program you were ineligible and you remained ineligible for life. Well if you had it just after you were eligible. And so we see that just a one week's difference in age across this cutoff means your probability of getting the vaccine suddenly jumps from zero percent to 50 percent. So again we've got really good comparison groups those who are just eligible and those who are just ineligible who must be similar to each other because all that's different for them is whether they were born just a few days earlier or a few days later. And this is what's so unique and different about our study and why our findings I think are so exciting.

Chris - How did you follow the people up and for how long?

Pascal - The beauty of the National Health Service in the UK is that it's a single provider, single payer health care system. So we see people in our data no matter which general practitioner they visit and we've been following them up for seven years in our primary follow up period and just see the strong strong protective signal for dementia.

Chris - Right so the people who got vaccinated were at much lower risk of dementia then?

Pascal - Absolutely. So our best estimate is a 20 percent reduction in new dementia diagnoses from shingles vaccination over the seven-year period which is a large effect size, much larger than for existing pharmacological tools. And because this is a readily available, inexpensive, one-off, safe intervention, I think this really has important implications for population health, dementia care and also research into what actually causes dementia.

Chris - What do you think the mechanism is? Do you think it's all centred on chickenpox, the virus itself, or do you think that the vaccine is doing something else and there's something else, nothing to do with the virus, might be having an effect on the nervous system? Can you get at that?

Pascal - I think there are two broad mechanisms that could be at play here and they're not mutually exclusive. So one of them is a chickenpox virus specific mechanism where the virus hibernates in your nervous system for life is in this constant interplay with the immune system and that causes some sort of inflammation process which through the shingles vaccine is reduced and that has benefits for dementia. The other mechanism is a virus independent mechanism which is a broader activation of the immune system, a boost to the immune system if you like, which is known to happen with many vaccines and particularly with this life attenuated vaccine that we have been studying and that these broader immune mechanisms have benefits for the development of dementia and Alzheimer's disease.

Chris - One way to get at that last point you made would be if you took a group of people who were having a vaccine but it wasn't the shingles vaccine and follow them up. So has anyone done that or do you have that sort of data where you could see they're also having something stimulating their immune system, nothing to do with chickenpox or shingles and they also have dementia or not?

Pascal - Absolutely, I think this is an important research agenda. However, this runs into this fundamental limitation that we have with most of these studies that all we can do is compare those who get the vaccine to those who don't get the vaccine and we know that people who go get vaccinated are very different to those who don't. They have got different health behaviors, different health characteristics, different dietary behaviors, physical activity levels, etc. And so those are not good comparison groups and becomes very hard to control for these variables because we usually don't measure them, don't have them in electronic health record data and that's why this shingles vaccination program is such a unique opportunity to get at cause and effect.

Chris - What's the best age for vaccination to stop shingles is one question but what's the best age for vaccination to stop dementia might be a totally different one and it might be that if you'd intervened at 70 not 80 you'd see an even bigger effect.

Pascal - Absolutely, yes, that's something that we can't address in our particular research but it's something that we would love to look at in future research.

Chris - What would your advice be then? Do you think that off the back of this you've got enough evidence to say to people ‘look for heaven's sake do not eschew the shingles vaccine because this might not just stop you getting shingles it might also stop you getting dementia?’

Pascal - Absolutely, we know that shingles vaccination has benefits for shingles prevention and so this knowledge that there may be an additional dementia benefit I think only provides additional motivation. However, I think really to convince the public health and medical community that this is a true cause and effect and should be a recommended approach for dementia prevention or delay I think for that we need a true randomised clinical trial on the effect of shingles vaccination on dementia and cognition and that's what I'm currently putting all my effort and energy into as our next research step and hoping for funds from private foundations and philanthropy to be able to get such a project off the ground.