Objective:

To assess seasonal influenza vaccine effectiveness (VE), including live attenuated influenza vaccine (LAIV) and inactivated influenza vaccine (IIV), against influenza-associated hospitalization among children aged 6–72 months in the Foggia district across four influenza seasons.

Approach:

• Design and population: Test-negative study of children hospitalized for acute respiratory infection and tested for influenza during the 2022–2023 through 2025–2026 seasons.
• Analysis: Compared vaccination status among influenza-positive cases and influenza-negative controls; 935 children with known vaccination status were included.

Key Findings:

• The cohort included 207 influenza-positive cases and 728 influenza-negative controls.
• At least one influenza vaccine dose was associated with adjusted pooled VE of 62.5% (95% CI, 34.4%–78.5%); full vaccination had VE of 61.9% (95% CI, 29.3%–79.4%).
• Adjusted VE for at least one LAIV dose was 80.3% (95% CI, 43.8%–93.1%); for at least one IIV dose it was 50.9% (95% CI, 6.9%–74.2%).
• VE against A(H1N1)pdm09 was 82.3% (95% CI, 25.2%–95.8%) for at least one dose. The A(H3N2) estimate was 43.5% (95% CI, −11.0%–71.3%) and was not statistically significant.
• VE against influenza B could not be estimated because no vaccinated influenza B cases were observed.

Interpretation:

In this study, influenza vaccination was associated with lower odds of influenza-associated hospitalization in the pooled analysis. Estimates varied by vaccine type and influenza subtype.

Limitations:

• The supplied context does not provide the study’s stated limitations.
• Subtype-specific estimates were unavailable for influenza B, and the A(H3N2) confidence intervals included no effect.

Sources:

• Article context supplied in the prompt