The Food and Drug Administration (FDA) has expanded the approval of Flucelvax® Quadrivalent (inactivated influenza vaccine; Seqirus) for active immunization in patients 2 years of age and older against influenza disease caused by influenza virus subtypes A and type B contained in the vaccine. Previously, the vaccine was approved for patients 4 years of age and older.

Flucelvax Quadrivalent is a subunit influenza vaccine manufactured using cell derived candidate vaccine viruses; it does not contain egg proteins or antibiotics. For patients aged 2 to 8 years, the vaccine is administered as 1 or 2 doses (0.5mL each) at least 4 weeks apart depending on vaccination history as per annual Advisory Committee on Immunization Practices (ACIP) recommendations. 

The expanded approval was based on absolute efficacy data from a multinational, randomized study that compared the efficacy, immunogenicity and safety of Flucelvax Quadrivalent to a non-influenza comparator in 4513 patients aged 2 to 17 years over 3 influenza seasons. Efficacy was assessed by the prevention of confirmed influenza illness caused by any influenza type A or B strain.

Results showed that overall vaccine efficacy for the entire study population was reported to be 54.6% (95% CI, 45.7-62.1), which met predefined success criteria. In children 2 through 8 years of age, vaccine efficacy was 50.5% (95% CI, 38.4-60.2), while in those 9 through 17 years of age, vaccine efficacy was 61.9% (95% CI, 47.4-72.3).

Flucelvax Quadrivalent is expected to be available for the 2021-2022 influenza season. The product is supplied in 0.5mL single-dose prefilled syringes and 5mL multi-dose vials.


1.    Seqirus announces U.S. FDA approval of expanded age indication of its cell-based quadrivalent influenza vaccine for people two years of age and older. [press release]. Summit, NJ: Seqirus; March 5, 2021. 

2.    Flucelvax Quadrivalent [package insert]. Summit, NJ: Seqirus; 2021.