# 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

## TL;DR

A study found that the 2023 XBB.1.5 booster offered limited protection against severe COVID-19 in older adults by summer 2024.

## Contribution

This study provides new evidence on the waning effectiveness of the XBB.1.5 booster against severe outcomes in older adults.

## Key findings

- VE against hospitalization was 13% for 65–79-year-olds and 7% for those ≥80.
- VE against death was 39% for 65–79-year-olds and 3% for those ≥80.
- Protection was minimal more than six months after vaccination.

## Abstract

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.

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.

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.

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.