Influenza is a seasonal condition that causes coughing, sneezing, mild fever and aches in most cases. However, it can sometimes take a serious turn, leading to hospitalization, especially for young children, adults over 65 and pregnant people. A recent study published in JAMA Network Open examined whether the high-dose inactivated influenza vaccine (HD-IIV), which contains four times as much antigen as the standard dose, offers superior protection against hospitalization and death.
Researchers analyzed data from eight large-scale clinical trials involving more than 600,000 participants that compared a high-dose flu shot with the standard flu shot in older adults.
The high-dose vaccine provided substantially greater protection, reducing the risk of flu-related hospitalization by 38.5% and hospitalization for laboratory-confirmed influenza by 31.2%. While the high-dose shot kept more people out of the hospital, it did not show a significant difference in preventing deaths compared with the standard shot.
Higher dose better?
It takes most people less than two weeks to recover from the flu, but the illness does not always end there. For some, the flu can lead to complications that prolong recovery or become serious enough to require hospitalization. Moderate complications, such as sinus and ear infections, can extend the recovery period.
In contrast, severe complications, such as pneumonia, can trigger other health problems, including inflammation of the heart and brain, as well as respiratory and kidney failure.
A standard flu shot helps reduce the risk of getting sick and protects against many of the flu’s potentially serious complications, but some populations need an extra boost. This led to the development of a high-dose flu vaccine (HD-IIV) for older adults, which contains 60 μg per strain compared with 15 μg in the standard dose.
This higher dose was designed to generate a stronger immune response in older adults, who often respond less effectively to the standard flu shot and are at greater risk of severe flu-related complications.
Earlier work showed the high-dose shot prevents more lab-confirmed flu infections than the standard dose. To shape flu vaccination guidelines for older adults, policymakers need evidence on whether high-dose flu vaccines meaningfully reduce hospitalizations and severe illness, not just mild infections.
A large study, FLUNITY-HD, combined data from two major trials—DANFLU-2 and GALFLU—and found that the high-dose flu vaccine was more effective than the standard vaccine at preventing flu-related hospitalizations.
In this study, researchers brought together findings from FLUNITY-HD and other randomized clinical trials to provide a clear picture of how high-dose and standard-dose flu vaccines compare in reducing hospitalizations and deaths among older adults.
These studies provided data on a large group of 605,098 participants across North America and Western Europe, including older adults living in their own communities and in nursing homes, as well as those with heart conditions.
Older adults who received the high-dose vaccine were less likely to be hospitalized for the flu and to have a lab-confirmed case of the flu compared with those who received the standard dose. The high-dose shot reduced hospitalizations for pneumonia or the flu by 11.5%, heart and lung problems by 7.5%, and all-cause hospitalizations by about 3%. The vaccine’s benefits held up across all age groups, including people over 80, and in those both with and without heart disease.
The findings show that for older adults, the choice of flu shot can make a real difference in their risk of hospitalization due to influenza complications. Public health planners can factor these results into strategies to protect health systems from being overburdened during flu season.