Effectiveness of Influenza Vaccines in Italy in the 2024/2025 Season: A Nationwide, Test-Negative Design Study Based...

The 2024/2025 influenza season in Italy was characterised by cocirculation of influenza A and B viruses. Monitoring influenza vaccine effectiveness (IVE) remains essential to guide public health policy due to antigenic shifts and varying strain circulation. In this study, we aimed to estimate IVE in primary care and hospital settings during the 2024/2025 season in Italy. A nationwide test-negative control design was used. Data were collected from the RespiVirNet surveillance system, encompassing both primary care and hospital settings. A total of 8842 participants were included in the primary care analysis and 2492 in the hospital analysis. Adjusted vaccine effectiveness (aVE) against any influenza virus was 69.0% (95% CI: 60.4%-75.9%) in primary care and 62.3% (95% CI: 45.9%-74.2%) in hospital settings. Effectiveness was highest among individuals under 18 years and decreased with age. Influenza B showed the highest aVE (83.6% in primary care; 95.0% in hospital settings), particularly among younger individuals. aVE for influenza A subtypes was lower, with A H1N1pdm09 (54.0% in primary care; 63.8% in hospital) and A H3N2 (60.1% in primary care; 45.5% in hospital) showing moderate effectiveness. The results suggest that influenza vaccines were effective in preventing medically attended influenza disease, both in primary care and hospital settings. These findings provide valuable insights for public health planning and vaccine policy in Italy.