A nationwide study of two decades of invasive pneumococcal disease in the Faroe Islands, 2000–2023

Background: Invasive pneumococcal disease (IPD) remains a significant public health concern, particularly in vulnerable populations such as the elderly. This study focuses on the Faroe Islands, a unique setting for monitoring pneumococcal disease trends due to its high vaccination coverage and geographic isolation. Objective: To examine the prevalence, trends and serotype distribution of IPD in the Faroe Islands from 2000 to 2023, focusing on the impact of pneumococcal conjugate vaccines (PCVs) on disease incidence and serotype replacement. Methods: Eighty-six pneumococcal isolates, representing all registered cases of IPD in the Faroe Islands, were analysed during the study period. Data on patient demographics, serotype identification and vaccination history were collected from national health records. Temporal trends in vaccine-type (VT) and non-vaccine-type (nVT) serotypes were analysed, particularly following the introduction of PCV13 in 2010. Results: Following the introduction of PCV13, a shift from VT to nVT serotypes was observed, while the overall IPD rate remained stable. Notably, there was an increase in IPD cases among the elderly population. The analysis indicated that serotype replacement contributed to a rise in nVT cases despite reducing VT-related IPD. Conclusions: The findings emphasise the need for ongoing evaluation of pneumococcal vaccine formulations and alternative strategies to address the increasing prevalence of nVT IPD. Higher-valency vaccines and sustained vaccination coverage are critical to mitigating the impact of serotype replacement and improving public health outcomes in the Faroe Islands.