A high-dose flu shot helps the body launch a stronger immune response against the flu than a regular-dose shot does, according to the Centers for Disease Control and Prevention. This is important for those 65 and older because their immune systems are weaker due to their age, and they benefit from the extra boost in immunity. The high-dose flue vaccine is only approved for use in those 65 and older.
Because the body's immune system weakens with age, seniors are more likely to get the flu and to suffer more serious symptoms than younger adults, explains the CDC. Seniors make up 90 percent of flu-related deaths and account for more than half of all flu-related hospital stays, according to FLU.gov.
A weakened immune system also means that the body launches a weaker immune response to vaccines; studies show that seniors produce between 50 and 75 percent fewer antibodies in response to normal-dose vaccines than younger adults produce, according to Mayo Clinic. High-dose vaccines contain four times the amount of antigen, the part of the virus that causes the body to produce antibodies, than the regular-dose vaccines contains, notes the CDC, and as a result, seniors produce more antibodies, resulting in 25 percent fewer cases of the flu, reports Mayo Clinic.