In the USA, over 65s are routinely vaccinated against the herpes zoster virus to prevent the onset of shingles. This virus is also the cause of chicken pox. In 2017, health care providers switched from a live vaccine called Zostavax to a more effective recombinant version called Shingrix.

This study looks at data from just over 100,000 people who were given the live vaccine from 2014-2017 and the same number who had the recombinant vaccine from 2017-202. All were over 65. Apart from the type of vaccine and the date they received it, the groups were very similar. All were followed up for four to six years after the vaccination to see how many were diagnosed with dementia (mostly Alzheimer’s Disease) in that time.

This study is straightforward, the number of patients involved is large and other factors that might affect the results have been ruled out, so the results are convincing.

The results were simple and clear: There was already some evidence that the old live vaccine was able to reduce the risk of Alzheimer’s Disease. This work shows that the new recombinant vaccine is even more effective, decreasing the likelihood of being diagnosed with dementia, if the new vaccine is used rather than the old one. Another way to look at it is that the age of onset of dementia is delayed by an average of 164 days, with a larger effect in women than men. This is a significant result, comparable in effectiveness to the recent antibody drugs for Alzheimer’s Disease. Administering the recombinant shingles vaccine could well be a simple and cheap way to lower the risk of Alzheimer’s Disease.

A link between infection with the herpes zoster virus and the onset of dementia has been suspected for some time, with Ruth Itzhaki from the University of Manchester first championing this idea, since the 1990s. As well as vaccines, a trial of the anti-viral drug Valacyclovir against Alzheimer’s Disease is currently underway.

Now, we need to run a clinical trial of the recombinant vaccine, comparing patients who receive the vaccine with those who get a placebo. This is the most reliable way to find out how well the vaccine works. We also need to see how many years the effect might last and whether we should vaccinate people at a younger age. We know that the path to Alzheimer’s Disease can start decades before any symptoms are apparent, so the vaccine might be even more effective if given to people in their 40s or 50s.

Though the herpes zoster virus as a cause of Alzheimer’s Disease is looking more and more likely, we must bear in mind that any such link is not simple. Most people who are infected by the virus never get Alzheimer’s Disease, and some who get the new recombinant vaccine get Alzheimer’s Disease regardless. A vaccine is therefore unlikely to ever totally prevent Alzheimer’s Disease. Many other factors affect the likelihood of getting dementia, such as genetics, cardiovascular problems and head injuries. Nevertheless, tackling the herpes zoster virus does look to be a promising strategy towards defeating this horrible and costly disease, and one that should be vigorously pursued.