ABSTRACT Background After a period of low SARS‐CoV‐2 activity, viral circulation increased in Europe from May 2024, driven by immune‐evasive KP sublineages of the JN.1 variant. We estimated vaccine effectiveness (VE) of the XBB.1.5 dose administered in autumn 2023 against COVID‐19‐related hospitalisations and deaths in individuals 65 years of age or older during this period. Methods We conducted a multi‐country cohort study across six EU nations in the VEBIS‐EHR network using linked electronic health records. VE against COVID‐19‐related hospitalisation and death during June–August 2024 was estimated using Cox regression in a two‐stage analysis, adjusting for demographics, comorbidities and prior vaccination history. Results Among individuals 65–79 and ≥ 80 years old, respectively, VE of the XBB.1.5 dose ≥ 6 months post administration was 13% (95% CI: −12% to 33%) and 7% (95% CI: −7% to 19%) against hospitalisation and 39% (95% CI: −7% to 65%) and 3% (95% CI: −23% to 23%) against deaths. Conclusions XBB.1.5 vaccination provided minimal residual protection against severe COVID‐19 outcomes among adults aged ≥ 65 years more than 6 months after vaccination, during the summer 2024 period of increased SARS‐CoV‐2 activity.
Ausenda Machado (2025) studied this question.