High-dose flu vaccine may benefit adults younger than age 65 years
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Key takeaways:
- A recombinant flu vaccine had a relative effectiveness of 15% compared with a standard dose vaccine.
- The finding was from a study of adults aged younger than 65 years.
A recombinant influenza vaccine offered additional protection against PCR-confirmed influenza and community-acquired pneumonia hospitalization among adults aged 50 to 64 years compared with a standard-dose vaccine, study results showed.
Although past studies have shown that high-dose influenza vaccines offer benefits for adults aged 65 years or older, “Data are needed on the relative effectiveness of recombinant vaccines as compared with standard-dose vaccines against influenza-related outcomes in adults under the age of 65 years,” Amber Hsiao, PhD, MPH, senior research project manager at Kaiser Permanente’s Vaccine Study Center, and colleagues wrote in The New England Journal of Medicine.
Their study compared the efficacy of two standard-dose, egg-based influenza vaccines with a high-dose recombinant influenza vaccine and found that the high-dose vaccine had a relative efficacy of more than 15% over the standard-dose vaccines.
In addition to containing three times the amount of hemagglutinin protein as standard-dose vaccines, recombinant vaccines are not susceptible to antigenic drift during manufacturing, which occurs in vaccine viruses grown in eggs. High-dose influenza vaccines have been recommended for people age 65 years or older since 2022.
“This large study adds to what we know about relative effectiveness of flu vaccines, which are given to millions of Americans each year, and on which we rely to reduce illness and hospitalization, particularly among vulnerable groups,” Hsiao said in a press release.
Hsiao and colleagues conducted a cluster-randomized observational study of 1.6 million people aged between 18 years and 64 years who received either the high-dose recombinant vaccine (38.8%) or a standard-dose vaccine (61.2%) at a Kaiser Permanente Northern California health facility during the 2018-2019 and 2019-2020 influenza seasons.
The primary outcome for the study was influenza confirmed by PCR testing among patients aged 50 years to 64 years, with secondary outcomes of influenza A, influenza B and influenza-related hospitalization outcomes.
PCR tests were performed on 16,340 study participants, with 23.4% testing positive for influenza — 1,386 cases in the recombinant group and 2,435 cases in the standard-dose group, according to the study.
Of PCR-confirmed influenza cases, 38% occurred among patients aged between 50 years and 64 years and 61.2% were in people aged 18 years to 49 years.
For patients aged between 50 years and age 64 years, 559 participants (or two cases per 1,000) tested positive for influenza in the recombinant vaccine group compared with 925 (2.34 cases per 1,000) positive tests in the standard dose group, for a relative vaccine effectiveness against influenza infection of 15.3% (95% CI, 5.9%-23.8%).
A secondary analysis identified a 15.7% relative vaccine effectiveness against influenza A infection among older participants in the recombinant group compared with the standard-dose group. Benefits against influenza B and hospitalizations were not significant, according to the study, but the researchers said a post hoc analysis combining PCR-confirmed influenza and hospitalization for community-acquired pneumonia found the recombinant vaccine reduced cases by 19.7% (95% CI, 2.8%-33.7%).
“If standard-dose vaccines were already preventing most cases of influenza and breakthrough cases of influenza, preventing 15% of breakthrough cases would be of modest public health benefit,” Hsiao and colleagues wrote. “However, since standard-dose vaccines prevent at most 40% to 60% of influenza cases annually, reducing the incidence of breakthrough influenza would provide a substantial public health benefit, especially during more severe influenza seasons.”
In subgroup and exploratory analyses, the relative vaccine effectiveness of the high-dose vaccine was 10.2% and 10.8% against influenza A and diagnosed influenza, respectively, among participants aged 18 to 49 years.
References:
- Flublok vaccine improved protections from flu for older adults. https://divisionofresearch.kaiserpermanente.org/flublok-vaccine-comparison/. Published Dec. 13, 2023. Accessed Dec. 14, 2023.
- Hsiao A, et al. N Engl J Med. 2023;doi:10.1056/NEJMoa2302099.
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