Annual influenza vaccinations reduced the risk for flu-related hospitalizations and medical visits for children by as much as two thirds, according to new research in Pediatrics.

However, researchers also found that less than half of the children received the immunization between 2021 and 2024.

The results are consistent with rates of vaccine effectiveness observed in seasons prior to the COVID pandemic, said Samantha M. Olson, MPH, an epidemiologist in the Division of Influenza at the CDC in Atlanta, who led the study.

“Even moderate vaccine effectiveness is translating to a meaningful reduction in flu hospitalizations, emergency department, and doctor’s visits for children,” Olson said. “We found this to be especially the case when we see high uptake of the vaccine.”

The study findings should help pediatricians reassure parents of the efficacy of the vaccine, Olson said. The 2024-2025 influenza season was among the deadliest for children in decades outside of the pandemic, with 280 flu-related deaths, according to the CDC. The American Academy of Pediatrics recommends the influenza vaccine for children aged 6 months or older.

The analysis included nearly 20,000 children aged 6 months to 17 years with acute respiratory illness who were tested for influenza at seven pediatric medical centers between 2021 and 2024. Children were considered vaccinated if they had received the seasonal influenza immunization at least 14 days before the onset of illness.

While effectiveness at preventing hospitalization and outpatient visits was lower at 34% during the 2021-2022 season, the rate climbed to 51% the following season and reached 60% during the 2023-2024 season. Roughly half of the children had been vaccinated each season.

Vaccine effectiveness was generally higher in younger children younger than 8 years, at 63% in the 2023-2024 season, than among older children (48% during the same season). Effectiveness also varied by circulating strain. Protection overall was the highest against influenza B (69%), followed by A/H1N1 (53%), and A/H3N2 (43%).

The data highlight an important clinical point: Influenza vaccination is not only about preventing infection but also about reducing disease severity, said Ravi Jhaveri, MD, division head of infectious diseases at Lurie Children’s Hospital of Chicago.

“At my hospital every year, we have children who never received a flu vaccine who may die or have a severe illness with several weeks in the hospital,” he said. “The regret and guilt these parents have is overwhelming.”

Cases of influenza have peaked since less Americans have received the vaccination following the COVID pandemic, a correlation Jhaveri said is “no coincidence.”

The study was funded by the CDC. Jhaveri reported serving as an advisor to Seqirus, Sanofi, and AstraZeneca and receiving research support from GSK and royalties from UpToDate. Olson reported receiving funding from Gates Foundation to attend a meeting. 

Brittany Vargas is a journalist covering medicine, mental health, and wellness.