Influenza epidemiology and vaccine effectiveness during the 2023/2024 season in Italy: A test-negative case-control study.

In order to support policymakers in allocating resources, we aimed to assess vaccine effectiveness (VE) of inactivated influenza vaccines (IIVs) available for Italian adults in the 2023/2024 season. A hospital-based test-negative case-control study was conducted in Genoa between mid-October 2023 and mid-April 2024. Adult (≥18 years) inpatients with prescription of a polymerase chain reaction test for influenza were eligible. Of 1,664 adults analyzed, most (82%) of which were ≥65 years, 114 (6.9%) tested positive for influenza A. Most (92%) cases were caused by subclades 6B.1A.5a.2a and 6B.1A.5a.2a.1 of the A(H1N1)pdm09 subtype. In older adults aged ≥65 years vaccination was effective at 51% (95% CI: 8%, 74%) against any influenza A and 49% (95% CI: 2%, 73%) against A(H1N1)pdm09. Compared with non-vaccinated older adults, VE point estimates for the adjuvanted and, especially, high-dose IIVs were higher than those for the standard-dose non-adjuvanted IIV. The 2023/2024 seasonal influenza vaccination proved moderately effective in preventing hospitalization for laboratory-confirmed influenza. Being more appropriate for older adults, local policymakers and vaccinating physicians should maximize adoption of the enhanced IIVs.

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Copyright © 2024. Published by Elsevier Ltd.

Déclaration de conflit d'intérêts

Declaration of competing interest A. D. provided consultancies and received speaker fees from CSL Seqirus, GSK and SD Biosensor and was previously (from 2016 to 2021) an employee of Seqirus S.r.L. A. O. provided consultancies and/or received speaker fees from CSL Seqirus, Moderna, Novavax and SD Biosensor. D. P. provided consultancies for Pfizer and CSL Seqirus and received grants for conducting observational studies from Sanofi, Pfizer, GSK and Viatris. G. I. provided consultancies and/or received grants for conducting experimental and/or observational studies for GSK, Sanofi, MSD, CSL Seqirus and Pfizer. Other authors declare no conflicts of interest.