Fluarix Strain Composition
Fluarix Quadrivalent contains four influenza virus strains: two influenza A subtypes (H1N1 and H3N2) and two influenza B lineages (B/Victoria and B/Yamagata), with 15 μg hemagglutinin of each strain per 0.5 mL dose. 1
Vaccine Formulation Details
Fluarix Quadrivalent is formulated to contain a total of 60 μg hemagglutinin (HA) per 0.5 mL dose, distributed equally among the four strains recommended annually for inclusion in quadrivalent influenza vaccines 1. This represents:
- 15 μg HA of influenza A(H1N1)pdm09 (the 2009 pandemic virus strain) 2
- 15 μg HA of influenza A(H3N2) 2
- 15 μg HA of influenza B/Victoria lineage 2
- 15 μg HA of influenza B/Yamagata lineage 2
Rationale for Quadrivalent Formulation
The inclusion of both influenza B lineages addresses a critical limitation of trivalent vaccines 3. Since the 2001-2002 influenza season, both B/Victoria-like and B/Yamagata-like viruses have co-circulated globally, making it difficult to predict which B lineage will predominate in any given season 4. Trivalent vaccines containing only one B strain showed limited protection when mismatches occurred between the vaccine component and circulating strains 4.
By incorporating both B lineages, Fluarix Quadrivalent reduces the risk of the dominant circulating B virus not matching the vaccine strain, providing broader protection than trivalent formulations 3. This is particularly important for children, who bear a substantial burden of influenza B disease 4, 5.
Clinical Immunogenicity
Fluarix Quadrivalent demonstrated non-inferior immune responses compared to trivalent vaccines for influenza A strains and the common B strain, while showing superior responses against the additional B strain 1. Importantly, the addition of the second B strain did not result in immune interference with other vaccine components 1.
Current Licensing
Fluarix Quadrivalent is currently approved for persons aged ≥6 months, with an approved dose volume of 0.5 mL for all ages 1. The vaccine is supplied in 0.5 mL single-dose prefilled syringes and administered by intramuscular injection 1.