Adults 65 and older are preferentially recommended to receive one of three enhanced flu vaccines: Fluzone High-Dose, Flublok (recombinant), or Fluad (adjuvanted). All three produce a stronger immune response than a standard flu shot, which matters because the aging immune system responds less robustly to conventional vaccines. If none of these three are available, a standard-dose flu vaccine is still recommended over skipping vaccination entirely.
Why Seniors Need a Stronger Vaccine
As you age, your immune system gradually loses its ability to mount a strong defense. The pool of new immune cells shrinks, existing cells become less effective at recognizing and attacking threats, and chronic low-grade inflammation interferes with the body’s ability to respond to vaccines. The result is that a standard flu shot, which works well in younger adults, simply doesn’t trigger enough of an immune response in most people over 65.
This isn’t a minor gap. Flu-related hospitalizations and deaths are disproportionately concentrated in older adults every season. The three enhanced vaccines address this problem through different strategies: packing in more of the active ingredient, adding a compound that amplifies the immune response, or using a manufacturing process that produces a more precise match to circulating viruses.
Fluzone High-Dose: Four Times the Antigen
Fluzone High-Dose, made by Sanofi, contains four times the amount of antigen (the component that trains your immune system) compared to a standard flu shot. The logic is straightforward: more antigen forces the immune system to produce more antibodies, compensating for the reduced responsiveness that comes with age.
Data from Denmark’s 2024/25 flu season found that the high-dose vaccine was 53% effective at preventing flu-related hospitalizations in adults 65 and older, compared to 33% for the standard-dose vaccine. That’s a meaningful real-world difference. The trade-off is that side effects are somewhat more common than with a standard shot. Soreness at the injection site, headache, muscle aches, and fatigue can occur, typically within the first week after vaccination.
Flublok: A Recombinant Approach
Flublok uses recombinant technology, meaning the active proteins are grown in insect cells rather than in chicken eggs. This avoids a common problem with egg-based manufacturing: the virus can mutate slightly as it adapts to growing in eggs, which sometimes makes the final vaccine a less accurate match to the flu strains actually circulating. Flublok’s proteins are exact copies of the ones found on wild flu viruses.
Flublok also contains three times the amount of active protein per strain compared to standard vaccines (45 micrograms versus 15 micrograms). Studies have shown it produces higher antibody levels, which is particularly relevant for older adults and people with weakened immune systems. Because it’s entirely egg-free, it’s also an option for anyone with a severe egg allergy, though that’s a secondary benefit for most seniors.
Fluad: Boosted With an Adjuvant
Fluad takes a different approach. Instead of increasing the amount of antigen, it includes an adjuvant, a compound that amplifies your immune system’s response to whatever antigen is present. Think of it as turning up the volume on the signal rather than repeating the message more times.
In the same Danish 2024/25 season data, the adjuvanted vaccine was 47% effective at preventing flu hospitalizations in seniors, compared to 33% for the standard vaccine. Overall effectiveness combining hospitalized and non-hospitalized patients was 48%, statistically similar to the high-dose vaccine’s 50%. In short, both enhanced options meaningfully outperform the standard dose, and neither has a clear edge over the other.
One practical note: if you’re getting your flu, COVID-19, and RSV vaccines at the same visit, your provider may prefer a non-adjuvanted flu vaccine (like Fluzone High-Dose or Flublok) when available, since some COVID-19 and RSV vaccines also contain adjuvants. Fluad can still be used if the other options aren’t on hand.
Cost and Coverage Under Medicare
All three enhanced vaccines are covered under Medicare Part B with no out-of-pocket cost. The standard Part B deductible and coinsurance do not apply to flu vaccines or their administration. This is true whether you get your shot at a doctor’s office, pharmacy, or clinic. Most private insurance plans for people 65 and older cover these vaccines at no cost as well, since flu vaccination is classified as preventive care.
When to Get Vaccinated
September and October are the ideal months. The CDC recommends that everyone be vaccinated by the end of October if possible. Getting vaccinated too early, in July or August, is discouraged for adults 65 and older specifically because immunity can wane over time, potentially leaving you less protected during the peak of flu season in January and February. If you can only make one trip and it happens to fall in August, getting vaccinated early is still better than not getting vaccinated at all.
Getting Multiple Vaccines at Once
You can receive your flu vaccine at the same visit as a COVID-19 vaccine, an RSV vaccine, or both. There’s no required waiting period between any of these. For many seniors, combining vaccines into a single pharmacy or clinic visit is the most practical approach. Each vaccine is given as a separate injection, typically in different arms or different sites on the same arm. Side effects from each vaccine can overlap, so you may feel more fatigued for a day or two compared to getting just one shot, but there’s no safety concern with co-administration.
Choosing Between the Three
Current evidence shows the high-dose and adjuvanted vaccines perform similarly in preventing hospitalizations among seniors, and the recombinant vaccine offers comparable enhanced protection. The CDC does not rank one above the others. In practice, your choice often comes down to which vaccine your pharmacy or doctor’s office has in stock. All three are a significant upgrade over a standard flu shot for anyone 65 or older, and the most important thing is getting one of them before flu season peaks.