What To Know About the High-Dose Flu Vaccine

In the US, flu season usually begins around October and ends around February, per the Centers for Disease Control and Prevention (CDC). If you're able to, you'll want to get a flu shot to be prepared and protected before the season arrives.

As you decide to get the flu shot, it's important to note that there are several types of flu vaccines available—from quadrivalent flu vaccines to recombinant flu vaccines. One vaccine in particular that you might be considering is the high-dose flu vaccine. However, the high-dose flu vaccine is not available for everyone. Here's what infectious disease experts say about the vaccine.

What Is the High-Dose Flu Shot, and Who Should Get It?

The high-dose flu shot is called the Fluzone High-Dose Quadrivalent, and it's the only licensed high-dose inactivated flu vaccine, according to the CDC. This vaccine has four components to help boost your immunity to the flu.

For adults 65 and older, the high-dose flu vaccine is recommended. "This type of vaccine contains a lot more viral protein, which is used to stimulate immunity, than the regular flu vaccine," infectious disease expert Amesh A. Adalja, MD, senior scholar at the Johns Hopkins Center for Health Security in Maryland, told Health.

Basically, the high-dose flu shot works in the same way as the regular flu shot—delivering inactivated virus to prompt the body to make antibodies. But it's associated with a stronger immune response.

According to an October 2019 article published in Cellular Immunology, 90% of flu-related deaths occur among older adults, and this population is more prone to flu-related complications. With this in mind, it makes sense why they should get the high-dose vaccine.

Your immune system typically becomes weaker as you age and, as a result, people who are 65 and older usually don't have immune systems that are as robust as their younger counterparts, Richard Watkins, MD, an infectious disease physician and professor of internal medicine at the Northeast Ohio Medical University, told Health. A weakened immune system also means that older people don't respond as well to the flu vaccination, the CDC says—as a result, they're given a stronger vaccine.

Why Isn't the High Dose Vaccine Recommended for Individuals Younger Than 65 Years Old?

Even though the vaccine is stronger, however, Dr. Adalja made the point that younger people simply don't benefit from the high-dose shot as much as older people do. Aside from that, there are plenty of other vaccine options available for those who are younger than 65 years old.

The CDC recommends that everyone 6 months and older get a flu vaccine every season, and advises going for a flu vaccine that's approved for your age group. Some inactivated flu vaccines, which use the inactivated version of the germ that causes a disease and provide less protection than live vaccines, are approved for people as young as 6 months. Other flu vaccines are only approved for adults, such as the recombinant influenza vaccine (RIV), which is approved for people aged 18 years and older.

Does the High-Dose Flu Shot Have Any Risks or Side Effects?

The CDC specifically states that the high-dose flu vaccine isn't recommended for people with a history of severe allergic reactions to the vaccine or to ingredients in the vaccines other than eggs. (You can ask your healthcare provider about the ingredients in the vaccine—which should be in the package inserts—if you have concerns.)

While studies have shown that the high-dose flu vaccine is more effective than the standard dose formulations for older adults, they've also shown an increased rate of mild to moderate local reactions, Richard Seidman, MD, chief medical officer at LA Care Health Plan, told Health. Additionally, the most common adverse events experienced during clinical studies were mild and temporary. These included pain, redness at the injection site, headache, muscle aches, and weakness.

What if the High-Dose Flu Shot Isn't Available?

If you or your loved ones can't get the high-dose vaccine from your health care provider, pharmacy, or another vaccine site, you can absolutely get the standard-dose vaccine as an alternative, Dr. Seidman said.

Keep in mind that, as of August 2022, there are three different flu vaccines that are designed for people aged 65 and up according to the CDC. One vaccine has the exact same amount of antigen (the part of the virus that triggers an immune response in your body) as the injection for younger adults. It also contains an adjuvant, which is an ingredient added that's designed to help you get a stronger immune response from the vaccine. The Fluzone High-Dose Quadrivalent vaccine has four times the amount of antigen, while the Fluzone Quadrivalent recombinant vaccine has three times the antigen amount.

"The adjuvanted flu vaccine is another vaccine specially formulated for older adults and would also be preferable to the ordinary flu vaccine in older age groups," Dr. Adalja explained. Per the CDC, the adjuvanted flu vaccine is made with MF59 adjuvant, an additive that triggers a stronger immune response to vaccination. Additionally, the recombinant vaccine can be a choice for those who are allergic to eggs, as it does not use eggs for its production.

Furthermore, if you want to get the high-dose flu vaccine, it's important to specify that instead of just assuming you'll be given it based on your age alone. Also, keep in mind that no vaccine is 100% effective in preventing the flu. "But even though a person can still get the flu after being vaccinated, there is evidence that the severity of the infection can be significantly less in patients who were vaccinated compared to those who were not," Dr. Seidman said.