Dose Differences Between Standard and Adjuvanted Influenza Vaccines
The adjuvanted flu vaccine (Fluad) contains the same amount of hemagglutinin antigen as standard-dose flu vaccines (15 μg per virus strain), but includes the MF59 adjuvant to enhance immune response, whereas standard-dose vaccines contain 15 μg per strain without adjuvant. 1
Key Dose Comparisons
Standard-Dose Influenza Vaccines
- Standard-dose vaccines contain 15 μg of hemagglutinin (HA) per vaccine virus in a 0.5-mL dose for persons aged ≥36 months 1
- For children aged 6-35 months, some formulations contain 7.5 μg of HA per vaccine virus in a 0.25-mL dose 1
- Total antigen content in quadrivalent formulations: 60 μg (15 μg × 4 strains) 1
- Total antigen content in trivalent formulations: 45 μg (15 μg × 3 strains) 1
Adjuvanted Influenza Vaccine (Fluad)
- Contains 15 μg of HA per vaccine virus (identical to standard-dose) in a 0.5-mL dose 1
- The critical difference is the addition of MF59 adjuvant, not increased antigen content 1
- Total antigen in trivalent formulation: 45 μg (15 μg × 3 strains) 1
- Licensed exclusively for persons aged ≥65 years 1
Why the Adjuvant Matters Despite Same Antigen Dose
The MF59 adjuvant enhances immune response through multiple mechanisms, allowing the same antigen dose to generate stronger immunity: 2, 3
- Adjuvants elicit more robust immune responses, particularly important in elderly patients with reduced immune function 1, 2
- The adjuvant provides cross-reactive immunity against antigenically divergent influenza strains 3
- This enhanced response occurs despite using the same 15 μg antigen dose as standard vaccines 1
Comparison with High-Dose Vaccine
For context, the high-dose vaccine (Fluzone High-Dose) takes a different approach:
- Contains 60 μg of HA per vaccine virus (4 times the standard dose) in a 0.5-mL or 0.7-mL dose 1
- Total antigen in trivalent formulation: 180 μg 1
- Also licensed for persons aged ≥65 years 1
- Achieves enhanced immunity through increased antigen rather than adjuvant 1
Clinical Implications
- Both adjuvanted and high-dose vaccines are preferentially recommended over standard-dose for adults ≥65 years 4, 5
- The CDC makes no preferential recommendation between adjuvanted and high-dose vaccines when both are available 4
- Recent comparative data show noninferior immunogenicity between adjuvanted and high-dose vaccines for most influenza strains in long-term care residents 6
Common Pitfall to Avoid
Do not assume adjuvanted vaccines contain more antigen—they contain the same 15 μg per strain as standard vaccines. The enhanced efficacy comes from the MF59 adjuvant's immunologic effects, not from increased antigen content. 1