High-dose flu vaccines are a type of vaccine approved for people age 65 and older. They can help people in this age group have a stronger immune system response against influenza, commonly called the flu.

Flu is an infection of the nose, throat and lungs, which are part of the respiratory system. Flu can be prevented with vaccination. The U.S. Centers for Disease Control and Prevention (CDC) recommends annual flu vaccinations for everyone age 6 months and older.

Some high-dose flu vaccines include 3 to 4 times as much flu virus antigen — the part of the vaccine that stimulates the immune system — as standard flu vaccines. One flu vaccine recommended for older adults has the same amount of antigen as the standard dose vaccine. But it boosts the immune response by including an ingredient called an adjuvant.

Why is it needed?

Flu data collected by the CDC shows that standard-dose flu vaccines likely don't work as well in people over age 65 as they do in younger populations. People age 65 and older are generally at higher risk than others for severe flu and complications. Rates for hospital stays and death linked to flu are generally higher in this age group than they are for younger people.

Looking at previous flu seasons, researchers found that among people age 65 and older, high-dose flu vaccines generally help prevent flu-related hospital stays better than the standard-dose flu vaccines do. Studies also have found higher antibody levels in older adults who received high-dose flu vaccines than in those who received standard-dose flu vaccines.

But any flu vaccination is better than none. So if you are approved to get a high-dose flu vaccine but it isn't available, get the flu vaccine that is available. Similar to other flu vaccines, the high-dose flu vaccine is updated every year to protect against the flu strains most likely to cause the flu during the upcoming flu season.

Are there side effects?

In a large study comparing high-dose and standard-dose flu vaccines, people who received the high-dose vaccine were more likely to develop side effects during the week after getting the vaccine. Side effects can include:

• Headache
• Soreness, pain or color change at the site of the shot
• Muscle aches
• Feeling very tired