High-dose flu vaccine better protects against hospitalization, infection than standard-dose
For the first study, published
in The Lancet, an international group of researchers, including two
from vaccine maker Sanofi, parsed pooled data from two large trials comparing
the efficacy of the high-dose inactivated influenza vaccine (HD-IIV) with the
standard-dose (SD-IIV) version against hospitalization for flu or pneumonia in
older adults.
The FLUNITY-HD trial was an individual-level pooled analysis
of two pragmatic randomized trials: DANFLU-2 in Denmark from 2022
to 2025 and GALFLU from
2023 to 2025 in Spain. In both trials, participants were randomly assigned to
receive either HD-IIV or SD-IIV and followed, starting 2 weeks later to May 31
of the following year, in each flu season.
At an estimated 515 older adults needed to be vaccinated
with HD-IIV instead of SD-IIV to prevent one all-cause hospitalization, a
simple switch from SD-IIV to HD-IIV could substantially reduce the burden of
influenza on health systems.
FLUNITY-HD included 466,320 adults with an average age of
73.3 years; 48% were women, and 48.9% had one or more chronic conditions.
Hospitalization for flu or pneumonia was documented in 0.56%
of the HD-IIV group, compared with 0.62% of SD-IIV recipients (relative vaccine
effectiveness [rVE], 8.8%). HD-IIV also lowered the rate of cardiorespiratory
hospitalization (2.02% vs 2.16% in the SD-IIV group; rVE, 6.3%), flu
hospitalization (0.11% vs 0.16%; rVE, 31.9%), and all-cause hospitalization
(8.54% vs 8.73%; rVE, 2.2%).
Hospital admission for flu occurred in 0.07% of HD-IIV
participants and 0.12% in SD-IIV recipients (rVE, 39.6%), and hospitalization
for pneumonia was documented in 0.50% and 0.51%, respectively (rVE, 2.3%).
Participants in both groups died of any cause with similar
frequency (0.61% vs 0.62%; rVE, 1.2%). The rate of serious adverse events was
comparable between groups (16,032 vs 15,857).
The findings "will inform evidence-based decision
making by health-care providers, policy makers, and immunization technical
advisory groups, contributing to potential optimization of influenza
vaccination strategies in the vulnerable older adult population globally,"
the authors wrote.
"At an estimated 515 older adults needed to be
vaccinated with HD-IIV instead of SD-IIV to prevent one all-cause
hospitalization, a simple switch from SD-IIV to HD-IIV could substantially
reduce the burden of influenza on health systems," they added.
29% greater protection against infection
The second study, published in
the International Journal of Infectious Diseases, used a
test-negative design to analyze inpatient and outpatient data from four studies
on older vaccinated adults tested for flu during the 2022-23 and 2024-25 flu
seasons.
The average patient age was 81.1 years, 52.1% were women,
and 87.2% had at least one chronic condition, primarily cardiovascular disease
(74.2%), respiratory conditions (27.0%), and diabetes (18.7%).
In this integrated analysis, Italian older adults
vaccinated with HD-IIV tended to report fewer laboratory-confirmed influenza
episodes than their counterparts vaccinated with SD-IIV.
A total of 102 (8.2%) flu cases were identified, all but two
(98.0%) of which were type A. Cases were almost evenly distributed among type
A(H1N1)pdm09 (52.0%) and A(H3N2) (48.0%).
Of 1,238 participants, influenza positivity was lower among
HD-IIV recipients than in the SD-IIV group (6.6% vs 10.3%; rVE, 29%). Relative
to SD-IIV, HD-IIV was 54% more effective against infection among adults aged 80
years and older.
In the entire cohort, rVE of HD-IIV versus SD-IIV estimated
using an unadjusted model was 40%, but when parsimoniously (28%) or fully (29%)
adjusted, the estimate wasn't statistically significant.
"In this integrated analysis, Italian older adults
vaccinated with HD-IIV tended to report fewer laboratory-confirmed influenza
episodes than their counterparts vaccinated with SD-IIV," the researchers
wrote. "This benefit was particularly evident in the oldest old, where the
observed rVE consistently indicated a meaningful effect, regardless of the
modeling strategy employed."
