We describe the burden of influenza B infections in Italy over a 12-year study period. Influenza A and B viruses co-circulated throughout the period, with numbers of influenza B cases approaching or exceeding those of influenza A during three influenza seasons. Influenza B virus infections led to fewer admissions to an intensive care unit (ICU) and a lower mortality rate than influenza A from 2010 to 2015. However, only 16% of those admitted to ICU with influenza B had been immunized. This highlights the need for consistent influenza vaccination for identified risk groups. Our study demonstrates that influenza B virus infections are associated with substantial morbidity and that influenza surveillance and interventions including vaccination and treatment are still suboptimal. Our findings have important public health implications. Incorporating virus and epidemiological data will help obtain more accurate estimates of influenza disease burden and result in a better selection of influenza prevention and control strategies.
Keywords: Epidemiology; Influenza B; Influenza impact; Vaccination; Vaccine mismatch.