Annual influenza vaccination is a widely recommended public health measure. Different vaccine formulations exist to provide tailored protection for various populations.
What High-Dose Flu Shots Are
High-dose flu shots differ from standard flu vaccines in their antigen content. Antigens are viral components that trigger an immune response. While a standard-dose inactivated flu vaccine typically contains 15 micrograms (mcg) of hemagglutinin (HA) antigen for each of the four influenza strains it covers, high-dose versions contain a significantly greater amount. For instance, Fluzone High-Dose Quadrivalent includes 60 mcg of HA antigen per strain. This increased antigen load is designed to stimulate a stronger immune reaction.
There are also adjuvanted flu vaccines, such as Fluad Quadrivalent, which contain the same amount of antigen as standard shots but include an adjuvant to enhance the immune response. Both high-dose and adjuvanted vaccines aim to produce a more robust antibody response.
Why High-Dose Flu Shots Are for Older Adults
High-dose flu shots are approved for individuals aged 65 years and older. This recommendation stems from immunosenescence, where the immune system naturally weakens with age. As people get older, their ability to mount a strong immune response to infections and vaccinations declines. This age-related immune dysfunction makes older adults more susceptible to severe influenza and its complications, including higher rates of hospitalization and death.
The higher antigen content in vaccines like Fluzone High-Dose Quadrivalent aims to compensate for this diminished immune response in older adults. Clinical studies have shown that high-dose vaccines induce a stronger antibody response in individuals 65 and older compared to standard-dose vaccines. This enhanced immune activation provides improved protection against influenza-related hospitalizations in this vulnerable population.
High-Dose Flu Shots for Those Under 65
High-dose flu shots are not generally recommended or approved for individuals under 65 years of age. For younger, healthy adults, standard-dose flu vaccines are considered effective and sufficient for protection against influenza. These standard vaccines have been shown to reduce febrile illness and provide significant protection against flu-related emergency department visits and hospitalizations in younger adults.
Despite the general recommendation, there are very limited “off-label” circumstances where a healthcare provider might consider a high-dose flu shot for someone under 65. This may occur in individuals with severe immunocompromise, such as those who have received organ transplants and are taking immunosuppressive medications.
For these specific patients, a high-dose or adjuvanted vaccine might be considered to help them mount a more adequate immune response, as their immune systems may not respond sufficiently to standard vaccines. Such decisions are made on a case-by-case basis after careful medical evaluation and are not a widespread recommendation for the general population under 65.