Effectiveness of the adapted bivalent mRNA COVID-19 vaccines against hospitalisation in individuals aged 60 years during the Omicron XBB lineage-predominant period: VEBIS SARI VE network, Europe, February to August, 2023

We conducted a multicentre hospital -based test -negative case-control study to measure the effectiveness of adapted bivalent COVID-19 mRNA vaccines against PCR-confirmed SARS-CoV-2 infection during the Omicron XBB lineage -predominant period in patients aged >= 60 years with severe acute respiratory infection from five countries in Europe. Bivalent vaccines provided short-term additional protection compared with those vaccinated > 6 months before the campaign: from 80% (95% CI: 50 to 94) for 14-89 days post -vaccination, 15% (95% CI: -12 to 35) at 90-179 days, and lower to no effect thereafter.