Study Shows Similar Effectiveness of Adjuvanted and High-Dose Influenza Vaccines in Older Adults
A landmark study published in JAMA Network Open has provided new clarity on influenza protection for the elderly, demonstrating that two specialized vaccine types offer similar levels of effectiveness. The research, conducted by CSL Seqirus, compared the performance of adjuvanted influenza vaccines (aQIV) and high-dose inactivated influenza vaccines (HD-QIV) among 430,000 adults aged 65 and older during the 2023/24 season.
The study utilized a large-scale cluster-randomized crossover design across various clinical settings. Researchers found no significant difference in the incidence of PCR-confirmed influenza between the two groups. Specifically, the aQIV group recorded 836 cases (3.9 per 1,000 people), while the HD-QIV group recorded 867 cases (4.0 per 1,000 people), establishing the non-inferiority of the vaccines.
Understanding Vaccine Efficacy and Clinical Impact
Beyond general infection rates, the study examined outcomes regarding emergency department visits and hospitalizations. Researchers found no significant variation in prevention efficacy between the two vaccines for PCR-confirmed influenza requiring emergency care or hospitalization. The study found no meaningful difference in the prevention of community-acquired pneumonia (CAP) hospitalizations.
Gregg Sylvester, Chief Medical Officer and Head of R&. D at CSL Seqirus, noted that these real-world evidence (RWE) findings provide critical data for shaping vaccination strategies. As individuals aged 65 and older account for a significant portion of influenza-related hospitalizations and deaths, identifying effective, specialized protection is a primary public health objective.
The U.S. centres for Disease Control and Prevention (CDC) estimated that individuals aged 65 and older accounted for 53% of all influenza-related hospitalizations during the 2025/26 season.
The significance of this research lies in its validation of current clinical guidelines. Since the 2022/23 season, the U.S. Advisory Committee on Immunization Practices (ACIP) has recommended prioritized access to adjuvanted, high-dose, or recombinant vaccines for seniors. This study reinforces those recommendations by confirming that both major specialized options offer comparable, high-level protection in real-world environments.
Future Implications for Public Health
Looking ahead, this data may assist health authorities in refining immunization programs globally. As the burden of influenza continues to disproportionately impact older populations—with the 65-plus age group experiencing the highest hospitalization rates—the availability of comparable, effective vaccine options provides flexibility in supply and strategic distribution.
Analysts expect that these findings will continue to support the use of specialized vaccines as a cornerstone of geriatric care. As health agencies in various regions, including South Korea, continue to manage national immunization programs, this real-world evidence may serve as a vital resource for optimizing vaccine strategies to further reduce the burden of severe influenza and its associated complications.
Frequently Asked Questions
What was the primary conclusion of the study regarding the two vaccines?
The study found no significant difference in efficacy between adjuvanted influenza vaccines (aQIV) and high-dose influenza vaccines (HD-QIV) for adults aged 65 and older, confirming their non-inferiority in preventing PCR-confirmed influenza.
How did the study measure the effectiveness of the vaccines?
The researchers conducted a large-scale cluster-randomized crossover study involving approximately 430,000 participants, tracking PCR-confirmed influenza cases, emergency department visits, and hospitalizations in real-world clinical settings.
Why are these vaccines recommended for the elderly?
Because the 65 and older population faces the highest burden of influenza-related illness, accounting for 70–85% of seasonal influenza deaths and 50–70% of hospitalizations, health authorities like the ACIP recommend specialized vaccines to provide enhanced protection for this high-risk group.
How do you believe these findings might influence your personal choices regarding annual flu immunizations?