Why Do Older Adults Need Enhanced Flu Vaccines?
As people age, their immune system naturally weakens, a process known as immunosenescence. This means that older adults' bodies do not mount as strong an immune response to a standard-dose flu vaccine as younger adults do. Consequently, they are at a higher risk of developing severe complications from influenza, such as pneumonia, which can lead to hospitalization and death. To address this challenge, health organizations like the CDC and the Advisory Committee on Immunization Practices (ACIP) preferentially recommend enhanced flu vaccines for adults aged 65 and older. These vaccines are specifically formulated to boost the immune system's response, providing better protection than standard-dose vaccines.
The Three Preferred Flu Vaccine Options for Adults 65+
For the 2025-2026 flu season, there are three types of enhanced flu vaccines recommended for seniors. All three are trivalent formulations, meaning they protect against three different strains of the influenza virus.
1. High-Dose Inactivated Flu Vaccine
This vaccine contains four times the amount of antigen—the part of the vaccine that stimulates the immune system—compared to a standard flu shot. The higher dose is designed to create a more robust antibody response. For the 2025-2026 season, the high-dose option is Fluzone High-Dose. Studies have shown that Fluzone High-Dose can be more effective at preventing flu in this age group compared to standard-dose alternatives. Side effects might be slightly more noticeable but are generally mild and temporary.
2. Adjuvanted Inactivated Flu Vaccine
This vaccine uses an adjuvant, an ingredient that is added to enhance the body's immune response to the vaccine. The adjuvanted flu vaccine, Fluad Quadrivalent, contains the same amount of antigen as a standard vaccine but the adjuvant boosts the immune system's reaction, leading to stronger immunity. Some research suggests it may also help lower the risk of flu-related complications and hospitalizations compared to standard-dose shots. It is important to note that Fluad is egg-based, though safe for most people with egg allergies.
3. Recombinant Flu Vaccine
The recombinant flu vaccine, Flublok, is egg-free and uses lab-made versions of the flu virus's antigen rather than growing the virus in eggs. It contains three times the amount of antigen as a standard dose, prompting a stronger immune response. The FDA has expanded the approval of Flublok for a broader age range, but it remains a recommended option for adults 65 and older. As an egg-free option, Flublok is a suitable choice for those with severe egg allergies.
Comparison of Enhanced Flu Vaccines for Seniors
| Feature | Fluzone High-Dose | Fluad (Adjuvanted) | Flublok (Recombinant) |
|---|---|---|---|
| Antigen Content | 4x standard dose | Standard dose | 3x standard dose |
| Mechanism | Higher dose of antigen stimulates stronger response | Adjuvant enhances immune response to standard antigen | Lab-made antigens stimulate strong immune response |
| Egg-Free? | No, egg-based | No, egg-based | Yes |
| Targeted Age | $\geq 65$ years | $\geq 65$ years | $\geq 9$ years (specifically recommended for 65+) |
| Key Benefit | Stronger immune response from more antigen | Stronger immune response from adjuvant boost | Egg-free, suitable for severe allergies |
| Common Side Effects | Mild, may be slightly more common (soreness, headache, aches) | Mild, may be slightly more common (soreness, headache, aches) | Mild, similar to standard vaccine |
Timing Is Important for Seniors
Another key consideration for seniors is the timing of their vaccination. Due to the potential for the vaccine's effectiveness to wane over time, the CDC recommends that adults 65 and older get vaccinated in September or October. This timing helps ensure peak protection during the months when flu activity is typically highest (December-February). Getting vaccinated in July or August is generally discouraged for this age group unless there is a risk they will not be able to get vaccinated later. However, it is never too late to get vaccinated, as flu viruses can circulate through May.
What if an Enhanced Vaccine Isn't Available?
If for any reason one of the preferentially recommended enhanced flu vaccines is not available, the CDC advises that any other age-appropriate inactivated flu vaccine should be administered. A standard vaccine is still better than no vaccine at all and provides a meaningful level of protection. In this scenario, it is important to proceed with vaccination to receive some protection against the flu, especially given the increased risk of severe illness for older adults.
Conclusion
For adults aged 65 and older, the Centers for Disease Control and Prevention (CDC) preferentially recommend one of three enhanced flu vaccines to provide a stronger immune response and better protection against serious flu complications. These include the high-dose (Fluzone High-Dose), adjuvanted (Fluad), and recombinant (Flublok) options. Each vaccine offers a different mechanism for boosting the immune system, with Flublok being the only egg-free option. The optimal time for vaccination is in September or October to ensure the longest-lasting immunity throughout the flu season. If an enhanced vaccine is not available, a standard flu shot is still recommended and provides a level of protection superior to remaining unvaccinated. Always consult your healthcare provider to determine the best choice based on your individual health needs.
For more information on the latest recommendations, you can visit the CDC's Flu and People 65 Years and Older resource.
