Hu W, DeMarcus LS, Sjoberg PA, et al. - Findings from the analysis from a large number of children aged 6 months-17 years over multiple influenza seasons suggest a moderate effectiveness of the inactivated influenza vaccination against influenza infection.

• A test-negative case-control study was conducted using the database developed from the US Department of Defense Global Respiratory Pathogen Surveillance Program over four consecutive influenza seasons from 2016 to 2020.

• Vaccine effectiveness (VE) analysis was performed including a total of 9,385 children including 4,063 medically attended, laboratory-confirmed influenza-positive cases.

• VE was estimated using a generalized linear mixed model with logit link and binomial distribution.

• For children, researchers recorded an overall adjusted VE of 42%, including 55% for influenza A (H1N1)pdm09, 37% for influenza A (H3N2), and 49% for influenza B.

• In the analysis by age groups, children aged 6 months-4 years were identified to have higher adjusted VE against influenza A (H1N1)pdm09 and influenza B, and comparable adjusted VE against influenza A(H3N2), when compared with those in children aged 5–17 years.

• Further age-stratified analysis showed that children aged 6–11 months exhibit low and non-significant VE against any types of influenza (33%), but it was high (54%) in children aged 12–23 months, and then a linear decline occur with increasing age.