Modern Flu Vaccines Provide Equal Protection for US Seniors

TOPLINE:

During the 2022-2023 influenza season, an adjuvanted quadrivalent influenza vaccine (aQIV) and high-dose (HD) QIV showed comparable effectiveness at preventing test-confirmed influenza among US adults aged 65 years or older across all hospital settings.

METHODOLOGY:

• Researchers conducted a retrospective study using the test-negative design to evaluate the effectiveness of the aQIV vs HD-QIV in preventing laboratory-confirmed influenza among US adults aged 65 years or older during the 2022-2023 influenza season.
• They analyzed data of 30,911 patients (mean age, 76.7 years) from a linked administrative claims database who had an acute respiratory or febrile illness, were tested for influenza within 7 days of diagnosis, and received either aQIV or HD-QIV.
• Patients who tested positive for influenza (n = 2361) were classified as cases, whereas those who tested negative (n = 28,550) were considered control individuals.
• The analysis was adjusted for demographic and clinical covariates, including insurance type, frailty index, healthcare utilization, comorbidities, and medical conditions associated with an increased risk for influenza complications.

TAKEAWAY:

• Overall, 31.8% and 68.2% received the aQIV and HD-QIV, respectively, with comparable rates of test-positive influenza between groups during the observation period (7.2% and 7.9%, respectively).
• The relative vaccine effectiveness (rVE) of aQIV vs HD-QIV showed no significant difference across all settings (adjusted rVE, -2.5%; P = .631) and emergency department/inpatient settings (adjusted rVE, 0.0%; 95% CI, -15.9% to 13.7%).
• During the peak season (6 November to 24 December 2022), 13.6% of aQIV and 14.4% of HD-QIV recipients tested positive for influenza, and the rVE in the sensitivity analysis was consistent with that in the main analysis.

IN PRACTICE:

“These findings align with current recommendations by ACIP [Advisory Committee on Immunization Practices] and other NITAGs [National Immunization Technical Advisory Groups] that support the use of adjuvanted and high-dose influenza vaccines in this age group,” the authors wrote.

SOURCE:

This study was led by Mahrukh Imran, CSL Seqirus, Kirkland, Quebec, Canada. It was published online on July 11, 2025, in International Journal of Infectious Diseases.

LIMITATIONS:

The observational study design introduced potential biases due to variability in the use of healthcare resources and heterogeneity inherent in the US healthcare system, which could not be fully accounted for. Vaccination was not randomized, and unmeasured confounding factors might have influenced the results. The limited sample size and data privacy constraints prevented a more detailed geographic analysis. Moreover, influenza testing was performed as part of routine care than according to preset screening criteria.

DISCLOSURES:

This study was supported by CSL Seqirus. Three authors reported being employees of CSL Seqirus and holding stock in CSL Limited. Three other authors reported being employees of Optum, which received funding from CSL Seqirus to support this work. One author reported receiving direct financial support from the study funders.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.