Effectiveness of the 2023 Autumn XBB.1.5 COVID-19 Booster During Summer 2024 in the EU/EEA: A VEBIS Electronic Health Record Network Study

We estimated the vaccine effectiveness (VE) of the XBB.1.5 dose given in the autumn 2023 against COVID-19-related hospitalisations and deaths in individuals 65 years of age or older across six EU countries reported following the 2024 summer peak in SARS-CoV-2 test positivity. A historical cohort study was performed by linking electronic health record databases. VE was estimated using Cox regression. Among individuals 65-79 years-old and ≥80 years-old, respectively, VE of the XBB.1.5 dose after ≥6 months post-administration was 13% (95%CI: -12%; 33%) and 7% (95%CI: -7%; 19%) against hospitalisation; and 39% (95%CI: -7%; 65%) and 3% (95%CI: -23%; 23%) against deaths. The 2023 autumnal dose showed very low to no effectiveness at the time of the period of increased SARS-CoV-2 spanning summer 2024.