Protective effect of influenza vaccine in Brazilian patients hospitalised for severe acute respiratory infection, 2023-2025

The study examined the effectiveness of influenza vaccine in patients hospitalized in Brazil with severe acute respiratory infection during 2023-2025. Vaccination rates declined from approximately 70 percent in 2023 to 40-50 percent in 2024 and 2025. A single vaccine dose reduced adverse outcomes by 10-13 percent compared to unvaccinated patients. However, two vaccine doses per year significantly reduced mortality by 32 percent, intensive care unit admissions by 52 percent, and intensive care unit stay by 28 percent. Researchers concluded that two doses of influenza vaccine were moderately effective in reducing in-hospital mortality and length of stay. Including individuals aged 50-59 years in a priority vaccination group could significantly reduce influenza-related adverse outcomes.