Flu vax linked to heart health
Although the protective effects may be small, the first two studies describe high-dose vaccines outperforming standard seasonal influenza vaccines in older adults.
Currently, high-dose vaccines are recommended for use
in adults 65 years and older, and they contain roughly four times the
antigen—the part of the vaccine that produces antibodies against influenza
virus—as standard-dose flu vaccines.
Myocarditis risk lower with high-dose vaccine
In the first study, based on findings from the Pragmatic
Randomized Trial to Evaluate the Effectiveness of High-Dose Influenza Vaccines
(DANFLU-2 trial) in JAMA Network Open, the risk of myocarditis or
pericarditis, or inflammation of the cardiac muscle or membrane around
it, was lower in people receiving the high-dose inactivated flu vaccine
than in those getting a standard-dose vaccine.
Influenza is a known risk factor for developing myocarditis
or pericarditis, and this large Danish study looked at the prevalence of the
inflammatory condition across three flu seasons, from 2022 to 2025. Of 332,438
participants randomized, 331,143 did not have a history of myocarditis or
pericarditis.
The incidence of myocarditis or pericarditis was lower among participants randomized to receive high-dose influenza vaccine compared to standard dose (19 vs 35 events; relative vaccine effectiveness, 45.7%; 95% confidence interval [CI], 2.5% to 70.7%).
Study suggests meaningful clinical benefit
Similarly, a secondary analysis of
the same Danish data in JAMA Cardiology finds a small
difference in the rate of cardiovascular events that favored the high-dose flu
vaccine compared to the standard dose, even among 91,026 participants (27.4%)
who had a history of cardiovascular disease.
During the 2022-23 and 2024-25 flu seasons, the incidence of cardiorespiratory hospitalization was 2.25% in the high-dose group, and 2.38% in the standard-dose group. The difference was driven primarily by a lower incidence of cardiovascular hospitalization (1.30% vs 1.40%), the authors said.
"Although the observed absolute differences in outcomes
may seem small, they could still represent a potentially meaningful clinical
benefit," they wrote.
In an editorial on
the study, Robert Califf, MD, wrote, "Because of its enormous statistical
power and the application of methods that only until recently were technically
impracticable, this trial deserves consideration in a broader context than the
specific comparison of the effects of 2 vaccine dosages on a specific
virus.
"I hope this study points the way toward a future in
which we have much more robust evidence to evaluate vaccines and other
therapies intended for broad segments of the population."
Heart patients do better with vaccination
Finally, a study across 164
hospitals in China found that administering the flu vaccine during
hospitalization for patients with acute heart failure was tied to a 17% lower
risk of all-cause mortality or any hospital readmission over 12 months.
The study, published in The Lancet,
provides strong evidence to support in-hospital use of influenza vaccination
for patients admitted with acute heart failure, the authors said.
Overall, 7,771 participants were enrolled at 164 hospitals
in each winter season between December 2021, and February 2024, with 3,570
assigned to the flu vaccination group and 4,201 to the usual-care (control)
group. Among those who were vaccinated, 88.1% received quadrivalent
(four-strain) forms of the vaccine.
In the primary analysis, 1,378 (41.2%) of 3,342 patients in
the vaccination group and 1,843 (47.0%) of 3,919 patients in the usual-care
group experienced the composite end point of all-cause mortality or hospital
readmission, which corresponded to an unadjusted odds ratio [OR] of 0.83 (95%
CI, 0.72 to 0.97).
"This translates to a number needed to vaccinate at the
participating hospitals of 27 (95% CI 14–500) to prevent one death or hospital
readmission," the authors wrote. "The number of patients with at
least one serious adverse event was significantly lower in the vaccination
group compared with the usual care group."
In a commentary on
the study, Ankeet Bhatt, MD, MBA, of Kaiser Permanente and Stanford University,
and Orly Vardeny, PharmD, of the University of Minnesota, write, "The
study is an impressive demonstration of implementation science across a wide
geographical distribution, including a large number of hospitals over three
influenza seasons—the investigators should be commended on their approach and
the rigor of this work."
"The observed effect on all-cause death and all-cause
hospitalization is noteworthy."
