An analysis of US national data finds a flu vaccine effectiveness (VE) against severe outcomes of 48% overall in kids in 2022-23, 53% among preschoolers, and 38% among children aged 9 to 17 years.
The study was published yesterday in Clinical Infectious Diseases. The 2022-23 flu season saw the highest influenza-associated pediatric hospitalization rate in the United States since 2010-11. Most of the illness was caused by the H3N2 strain.
Outcomes were based on pediatric patients seen at 55 hospitals and 107 emergency department (ED) or urgent care (UC) sites through Kaiser Permanente Northern California, Intermountain Healthcare in Utah, and HealthPartners in Minnesota and Wisconsin.
40% protection against hospital cases
The VE for vaccinated children against emergency department and urgent care (ED/UC) visits was 48% (95% confidence interval [CI], 44% to 52%). The study showed that 15.2% of vaccinated kids and 27.1% unvaccinated children made up ED/UC flu patients.
The VE against hospital admission for the flu was 40%. Among kids hospitalized for the flu, 17.5% were vaccinated and 33.4% were unvaccinated. The authors of the study said lower VE may be due to lower vaccine coverage.
The atypically early start of the 2022–2023 influenza season may have resulted in lower observed vaccine coverage.
"The atypically early start of the 2022–2023 influenza season may have resulted in lower observed vaccine coverage, as activity started and peaked before many children and adolescents may have had an opportunity to get vaccinated," they wrote.