The high-dose flu shot is associated with an almost 40% greater reduction in severe illness among older adults than is the standard-dose flu vaccine, according to a new study in JAMA Network Open.
The high-dose formulation, which contains four times the antigen of a standard-dose inactivated influenza vaccine, is given to older adults, who tend to have a lower immune response to vaccinations and are at higher risk of flu-related hospitalization. The antigen is the “active ingredient” of a vaccine, the component that produces an immune response.
The meta-analysis found that the high-dose vaccine was associated with a 38.5% reduction in flu-related hospitalizations among adults aged 65 years or older when compared with standard-dose flu vaccines, as well as greater protection against flu-related pneumonia and cardiorespiratory disease. The study authors say it’s the “most comprehensive synthesis to date” of evidence on the relative effectiveness of high-dose versus standard-dose flu shots.
These findings reinforce the Centers for Disease Control and Prevention's recommendation that older adults receive the high-dose version of the flu shot, said William Schaffner, MD, an infectious diseases researcher at Vanderbilt University Medical Center.
"The vaccine is not perfect. It cannot prevent every infection. But it reduces the risk of severe disease," said Schaffner, who did not contribute to the study.
High-dose vaccine probably also prevents more deaths
If severe illness is reduced, then logically, that benefit would extend to a greater reduction in mortality. Paradoxically, the researchers did not find the high-dose shot to prevent fewer flu-related deaths than the standard-dose vaccine prevents.
It's likely the eight studies in the meta-analysis, which included 605,098 participants in Europe and North America, didn't track patients for long enough to show this benefit, said Schaffner.
Additionally, flu-related fatalities are rare compared with hospitalizations, explained Edward Belongia, MD, a vaccine researcher and infectious disease epidemiologist, who was also not involved in the study.
But if the high-dose vaccine is preventing hospitalizations, Belongia said a reasonable conclusion is that it prevents more deaths, along with serious long-term disability, which can be devastating.
The study was funded by the pharmaceutical company Sanofi, which produces the high-dose flu shot.
Neither Schaffner nor Belongia, who is retired, receives funding from Sanofi. Both told CIDRAP News that they see no indication that the study's authors tipped the scales to generate more favorable results.
