Effectiveness of quadrivalent influenza vaccine based on the test-negative control study in children during the 2016-2017 season

The participants were divided into three age groups (group A: 0-4 years old, group B: 5-9 years old, and group C: 10-15 years old); in group A, the adjusted VE of quadrivalent influenza vaccine was significant for any influenza (A + B): 58.6% (95% CI: 28.8-76.0), influenza A: 53.9% (95% CI: 16.4-74.6), and influenza B: 78.6% (95% CI: 23.6-94.0). In both groups B and C, VE was not observed for any of the types of influenza. In only group A, two doses of vaccines provided significantly better VE against any influenza, as well as both influenzas A and B, than single-dose vaccines and cases in which vaccination was not administered. In conclusion, quadrivalent influenza vaccine showed significant VE and dose-dependent VE against any influenza and both influenzas A and B, in children aged 0-4 years during the 2016-2017 season. Both the VE and dose-dependent VE were almost not observed in older group. However, this may due to low rate of vaccination, particularly in children aged 10-15 years.