GSK said on Tuesday that it is studying a group of more than a million older adults in the UK to examine whether its best-selling shingles vaccine lowers the risk of dementia.

The British drugmaker is using the health data of some 1.4 million people, aged 65 to 66, some of whom received its Shingrix shot and some who did not.

GSK's chief scientific officer Tony Wood said the data, from the state-run National Health Service's (NHS) large database, is a unique set of information because due to a tweak in the UK's shingles immunization program there is effectively a naturally randomized trial already taking place.

When the national vaccine program expanded in 2023, 65-year-olds upwards became eligible for the Shingrix vaccine, whereas previously only people aged 70 and over were eligible. However, those aged 66 and over at the time of the expansion were informed they could not get it until they turned 70. This meant two large patient groups were randomly assigned to distinct vaccination groups.

It would be "prohibitively expensive" to run a trial on such a large group, Wood said on a media call. "So this is a partnership which allows us to answer a question which one could not really conceive of answering under normal circumstances."

The study will examine the data until the 66-year-olds turn 70 and become eligible for the vaccine, taking into account factors such as other medical conditions.

Research has already shown that vaccines against the viral infection shingles potentially reduces the risk of dementia, but past studies only identified associations, not causality.

The new study, in partnership with the UK Dementia Research Institute and Health Data Research UK, will assess the dementia question more definitively. If confirmed, GSK could discuss the data with regulators in hopes of securing an expanded label for the jab.

More than 55 million people globally have dementia. For decades the field of Alzheimer's research was littered with failures, but now a number of clinical trials are underway or completed for a group of Alzheimer's vaccines that could finally lead to breakthrough therapies.