Which Flu Shot to Choose If You're Over 65

To stave off winter illness, now is a great time for all of us-especially older adults-to get updated flu and COVID shots. If you are over 65, you may want to consider a high-dose or adjuvanted version of the flu shot. These formulations are recommended for older adults, since they may be more effective. (That said, the CDC says the regular flu shot is fine if you can't conveniently access the preferred formulations for your age group.)

Which are the preferred flu shots for older adults?

These are the three shots that the CDC recommends getting, if you can, if you are 65 or older:

• A high-dose flu shot.

• A recombinant flu shot, which also happens to be egg-free.

• An adjuvanted flu shot.

I'll walk you through what these terms mean, and why these shots are considered to be better for older adults. But you don't need an in-depth understanding of the differences to make an appointment at your local pharmacy. Just ask whether they have any of the vaccines above, and if they do, get one of those in preference to the other, "regular" flu shots.

What does "high dose" mean, and why is that a good thing?

The way a vaccine works is to expose your immune system to a little bit of antigen. The antigen is something that the immune system can recognize and later respond to; in many flu vaccines, the antigen is an influenza virus that has been killed and ripped into pieces. (That's why the flu shot cannot give you the flu.)

As we age, our immune system sometimes doesn't respond as strongly as it did when we were younger, so a regular flu vaccine may not spur as strong an immune response as we need for the vaccine to be effective. One way around this is to just give more antigen. That's the idea behind the high-dose shot: it just contains more of those virus pieces. Specifically, four times more.

Side effects are slightly more common with the high-dose flu vaccine than with the regular kind, but they're the same types of side effects anyone might get from a flu shot, and like the regular flu shot, they are not usually serious. The CDC says: "The most common adverse events experienced during clinical studies were mild and temporary, and included pain, redness at the injection site, headache, muscle aches, and malaise."

What does "adjuvanted" mean?

Instead of a high-dose flu vaccine, another extra-strength option for older adults is an adjuvanted vaccine. Instead of a higher dose of the antigen, it contains an adjuvant, which is an ingredient that makes your immune system react more strongly. (The adjuvant in this case is squalene oil, also called MF59.)

Like the high dose vaccine, adverse effects for this vaccine are slightly more common than with a standard flu vaccine, but do not tend to be serious. The CDC says: "The most common adverse events experienced during clinical studies were mild to moderate and were temporary, and included pain, redness at the injection site, headache, muscle aches, and malaise."

What is a "recombinant" flu shot?

The term "recombinant" refers to the way the virus particles were manufactured for the vaccine. Traditionally, flu vaccines were made with a process that involved chicken eggs. There is also a newer, cell-culture-based vaccine that does not use eggs. And then there is a third type: the recombinant vaccine.

As the CDC explains, a recombinant vaccine doesn't use flu viruses at all in its manufacturing. Instead, a portion of the flu virus's genome is added to a different type of virus ("recombinant" means that different bits of genetic material are combined together) and this virus is grown in cells and then the portion that contains the influenza virus protein is purified out and used to make the vaccine.

The recombinant vaccine is available for all age groups, not just older adults. It is one of the preferred vaccines for older adults because it contains more antigen than the other, regular flu vaccines, and has been shown to work well for older adults.

If I'm over 65, do I need a special flu shot?

The CDC says that any flu shot is fine if it's been approved for people in your age group. But there are three flu vaccines that are specifically for adults who are 65 and older.

There haven't been randomized studies comparing these three vaccines to each other, the CDC says, but there is evidence showing that each vaccine works better for people over 65 (preventing cases of the flu, and reducing hospital admissions) than the standard vaccine.

Complications of the flu are especially likely to be serious in older people, with those over 65 accounting for more than half of hospitalizations and more than 70% of deaths according to a 2013 study. Therefore, flu shots are especially important in this age range.