Herpes zoster incidence in adults aged ≥ 20 years in Finland, 2015 to 2023: a population-based register study.

BACKGROUNDHerpes zoster, also known as shingles, is a painful skin condition caused by varicella zoster virus. Information is lacking on incidence of herpes zoster in Finland.AIMTo estimate age-specific annual incidence of herpes zoster over 9 years with data from several nationwide health registers.METHODSIn a nationwide study, we compiled a dataset encompassing the entire Finnish population by linking data from multiple population-based registers for 2015-23. The dataset includes records from nearly all healthcare providers in Finland. Case definitions were based on ICD-10 codes B02 and G53.0, and ICPC-2 code S70. The dataset was supplemented with information on the purchase of prescribed antiviral medication.RESULTSIn total, 220,693 herpes zoster cases were identified during 2015-23 among adults aged ≥ 20 years. In 2023, when register coverage was best, age-specific annual incidence rates for the entire population varied from 3.8 to 12.2, increasing with age. Incidence was higher among females than males, and highest among elderly aged ≥ 85 years living at home without organised care. Cumulative incidence data from 2023 revealed that lifetime risk of developing herpes zoster by age 85 was 42%, and as high as 46% using the incidence among elderly living at home without organised care.CONCLUSIONHerpes zoster incidence varied by sex and age group, and appeared to be under-reported in institutional and organised care settings. Currently, there is no official decision on herpes zoster vaccination in Finland, despite favourable recommendations from the national expert group and the National Advisory Committee on Vaccination.