We conducted a multicentre test-negative case-control study covering the period from October 2023 to January 2024 among adult patients aged ≥18 years hospitalised with severe acute respiratory infection in Europe. We provide early estimates of the effectiveness of the newly adapted XBB.1.5 COVID-19 vaccines against PCR-confirmed SARS-CoV-2 hospitalisation. Vaccine effectiveness was 48% overall, ranging between 68% at 14–29 days and 40% at 60–105 days post vaccination. The adapted XBB.1.5 COVID-19 vaccines conferred protection against COVID-19 hospitalisation in the first 3.5 months post vaccination, with VE >70% in older adults (≥65 years) up to 1 month post vaccination.

We conducted a multicentre hospital-based test-negative case–control study to measure vaccine effectiveness (VE) against PCR-confirmed influenza in adult patients with severe acute respiratory infection (SARI) during the 2022/23 influenza season in Europe. Among 5547 SARI patients ≥18 years, 2963 (53%) were vaccinated against influenza. Overall VE against influenza A(H1N1)pdm09 was 11% (95%CI: -23–36); 20% (95%CI: -4–39) against A(H3N2) and 56% (95%CI: 22–75) against B. During the 2022/23 season, while VE against hospitalisation with influenza B was >55%, it was ≤20% for influenza A subtypes. While influenza vaccination should be a priority for the upcoming season, improved vaccines against influenza are needed.