Incidence of herpes zoster among immunosuppressed compared to general population in Finland, 2021-23

Abstract Background Varicella zoster virus can reactivate as Herpes zoster (HZ) when the immune system weakens. As a new, effective but expensive vaccine is available, we aim to determine the incidence of HZ in immunocompromised individuals and compare it with the incidence in the general population. Methods We identified all HZ cases in Finland during 2021-23 from healthcare registers through healthcare contacts using ICD10 (B02, G53.0) and ICPC2 (S70) codes, and from purchases of specific antiviral therapy medication. Thereafter, we formed the immunocompromised groups by using the same data sources, both diagnoses of illnesses and immunosuppressive medications purchased, and compared the incidence of HZ among various immunocompromised groups and population in general. Results A total of 79,727 HZ cases were identified in Finland among adults during 2021-2023. The highest annual incidences were found among patients with organ or bone marrow transplants or hematologic cancers: 27.4-30.7 cases per 100,000 among individuals aged 60-69, and 24.6-28.0 among those aged 70-79, over the three-year period. Among patients with immunosuppressive medications for autoimmune diseases, the incidence ranged from 13.4 to13.9 cases per 100,000 in the 60-69 age group, and 12.9 to 14.3 in the 70-79 age group. In the general population, the incidence of HZ was 7.2-7.8 cases per 100,000 in the 60-69 age group and 9.3-10.0 in the 70-79 age group. Conclusions The most immunosuppressed i.e. organ or bone marrow transplant or hematologic cancer patients have a high annual incidence of HZ. The cost-effectiveness of new effective but expensive HZ vaccinations should be estimated especially among them. Key messages • The highest annual incidences of Herpes zoster were among patients with transplants or hematologic cancers: roughly 30 cases per 100,000 among 60–69 year of age, and 25 among those aged 70–79. • The risk of HZ zoster was 3-4 times higher among the most immunosuppressed compared to the general population in Finland, and vaccination should be considered among these groups in particular.