Experts considered the 2024-25 influenza season severe, the most serious since the 2017-18 season. Vaccination against flu protected US adults and children from hospitalization and needing outpatient medical care, according to a paper published last week in Open Forum Infectious Diseases.
“These findings support influenza vaccination as an important tool to reduce influenza-associated morbidity and mortality across the lifespan,” wrote the authors, led by researchers at the Centers for Disease Control and Prevention (CDC).
43% to 54% vaccine effectiveness
Using a test-negative, case-control design, scientists examined the electronic records of patients who visited one of seven Virtual SARS-CoV-2, Influenza, and Other (VISION) sites to understand how well the flu vaccine prevented hospitalizations and emergency department and urgent care clinics (ED/UC) from October 2024 to April 2025. They looked at healthcare interactions in children ages 6 months to 17 years, as well as adults.
The data included 5,764 pediatric hospitalizations and 102,854 ED/UC visits. Among adults, 76,072 were hospitalized, and 233,411 sought outpatient treatment.
In total, 17% of children and 28.2% of adults were vaccinated. For children, the vaccine was 51% effective against flu-related hospital stays and 54% effective against ED/UC visits. Vaccine effectiveness in adults was 43% against hospitalization and 49% against ED/UC visits.
These findings support influenza vaccination as an important tool to reduce influenza-associated morbidity and mortality across the lifespan.
The researchers found that vaccines were most effective during the first two months following vaccination, after which protection waned.
“Seasonal influenza vaccination provided protection against influenza-associated hospitalizations and ED/UC encounters among US children and adults during the 2024-25 season,” the authors wrote. “Protection was also observed against critical illness, including ICU [intensive care unit] admissions in children and ICU admissions and deaths in adults.”