The purpose of this study is to evaluate the effect of the recombinant zoster vaccine on the risk of new diagnosis of dementia among adults aged 76 years or older in Finland. Participants will be enrolled and randomized in a 3:1 ratio to receive either recombinant zoster vaccine or placebo.

Inclusion Criteria:

• Citizens living permanently in Finland, who, in the opinion of the investigator, can and will comply with the requirements of the protocol.
• Written or witnessed informed consent obtained from the participant prior to performance of any study-specific procedure. Informed consent will include consent to access health register data for participants.
• Age 76 years or older at the time of signing the informed consent.

Exclusion Criteria:

• Prior receipt of a Herpes Zoster (HZ) vaccine.

• History of dementia diagnosis prior to enrolment, including confirmed cases or those under investigation. This includes:

  • History of a confirmed clinical diagnosis of dementia prior to enrolment.
  • Prior or current use of medications intended to treat dementia.
  • Current or recent history of cognitive assessments for any memory deficit or suspected dementia before enrolment including investigations that are ongoing or that were inconclusive (but not those for which dementia was conclusively ruled out); mild cognitive impairment on its own without any other information to indicate cognitive decline or dementia will not result in exclusion.

• Severely immunocompromised individuals.

• Concurrently participating in another clinical trial, in which the participant has been or will be exposed to an investigational product or ongoing participation in trials focused on preventive dementia interventions.

• Known systemic hypersensitivity to any of the vaccine components, or history of a life-threatening reaction to the vaccines used in the study or to a vaccine containing any of the same substances.

• Living in a nursing facility.

Study Sponsor will assess requests from qualified researchers for anonymized individual patient-level data and related study documents. Data sharing is subject to certain criteria, conditions, and exceptions. For further information, refer to https://d3l8i7lo48obsd.cloudfront.net/gsk-patient-level-data-sharing-july2025-1-Bgwa1UthxvluYbWYTThw.pdf

Anonymized IPD will be made available within 6 months of publication of primary, key secondary and safety results for studies in product with approved indication(s) or asset(s) with development terminated across all indications.

Anonymized IPD is shared with researchers whose proposals are approved by an Independent Review Panel and after a Data Sharing Agreement is in place. Access is provided for an initial period of 12 months, but an extension may be granted, when justified, for up to 6 months.

Data will be collected in an observer-blinded fashion.