Every influenza season places older adults at significantly higher risk of severe illness, hospitalization, pneumonia, and death. Adults aged 65 years and older experience a natural decline in immune responsiveness—known as immunosenescence—which reduces the effectiveness of standard influenza vaccines.

For this reason, Canadian influenza guidelines have increasingly recommended enhanced influenza vaccines for seniors, specifically:

• High-dose influenza vaccines
• Adjuvanted influenza vaccines

A major new real-world study from the United States now provides important evidence comparing these two enhanced vaccine options directly in older adults.

The findings are reassuring: both vaccines performed similarly well in preventing laboratory-confirmed influenza and serious flu-related complications.

At Orleans Family Health Clinic (OFHC), this information helps support evidence-based discussions with older patients about influenza prevention and seasonal vaccination planning.

Why Influenza Is More Dangerous in Older Adults

Influenza is not simply a “bad cold” in seniors.

Older adults are more likely to experience:

• Severe respiratory illness
• Secondary bacterial pneumonia
• Exacerbations of chronic conditions such as COPD, asthma, heart failure, and diabetes
• Hospitalization
• Functional decline after illness
• Increased mortality

Even healthy older adults can develop serious complications from influenza infection.

Vaccination remains the most important preventive intervention available.

What Is the Difference Between High-Dose and Adjuvanted Flu Vaccines?

High-Dose Influenza Vaccine

High-dose influenza vaccines contain a larger amount of antigen—the component that stimulates the immune system.

The goal is to generate a stronger immune response in older adults whose immune systems may respond less robustly to standard vaccines.

Examples include:

• Fluzone High-Dose Quadrivalent

Adjuvanted Influenza Vaccine

Adjuvanted vaccines contain an ingredient called an adjuvant, which enhances the body’s immune response to vaccination.

The adjuvant helps “boost” immune recognition and improve protection against influenza strains.

Example: Fluad

The New Study: Comparing the Two Vaccines

Researchers from Kaiser Permanente Northern California conducted one of the largest real-world comparative influenza vaccine studies ever performed in older adults.

Study Design

The study:

• Included adults aged 65 years and older
• Occurred during the 2023–2024 influenza season
• Included over 429,000 participants

Compared:

• Adjuvanted influenza vaccine (Fluad)
• High-dose influenza vaccine (Fluzone High-Dose and recombinant high-dose formulations)

Importantly, this was not merely an observational database review. Facilities alternated vaccine formulations weekly in a randomized crossover design, improving the reliability of comparisons.

Researchers evaluated:

• PCR-confirmed influenza infections
• Influenza-associated emergency department visits
• Influenza-associated hospitalizations
• Hospitalization for community-acquired pneumonia

Key Findings

Both Vaccines Performed Similarly

The study found that:

• The adjuvanted vaccine was noninferior to the high-dose vaccine
• Both vaccines offered comparable protection against laboratory-confirmed influenza

In practical terms:

• Neither vaccine demonstrated a clinically meaningful superiority over the other

Influenza Infection Rates Were Nearly Identical

Among more than 429,000 vaccinated older adults:

• 836 influenza cases occurred after adjuvanted vaccination
• 867 influenza cases occurred after high-dose vaccination

These rates were extremely close.

Protection Against Serious Outcomes Was Also Comparable

Researchers also found similar protection against:

• Influenza-related emergency visits
• Influenza-related hospitalization
• Community-acquired pneumonia hospitalization

This is particularly important because preventing severe complications—not merely mild infection—is one of the primary goals of influenza vaccination in seniors.

What Does “Noninferior” Mean?

In medical research, a “noninferior” result means one treatment performed at least as well as another within clinically acceptable margins.

This study supports the conclusion that:

Adjuvanted influenza vaccines and high-dose influenza vaccines are effectively equivalent options for adults aged 65 years and older.

What This Means for Patients

For older adults, the most important message is:

Receiving an enhanced influenza vaccine matters more than which enhanced vaccine is chosen.

Both vaccine types:

• Improve immune response compared with standard-dose vaccines
• Provide stronger protection for seniors
• Help reduce complications and hospitalization risk

If one enhanced vaccine is unavailable, the other remains an excellent option.

Canadian Recommendations for Seniors

Canadian influenza guidance continues to preferentially recommend enhanced influenza vaccines for adults 65 years and older whenever available.

This includes:

• High-dose influenza vaccines
• Adjuvanted influenza vaccines

The new evidence supports flexibility in vaccine selection while maintaining strong protection for older adults.

Why Annual Influenza Vaccination Remains Essential

Influenza viruses evolve constantly, which is why annual vaccination remains necessary.

Protection from prior vaccination also declines over time.

Annual flu vaccination helps:

• Reduce severe disease risk
• Lower hospitalization rates
• Protect vulnerable household members
• Reduce strain on healthcare systems during respiratory virus season

For older adults with chronic medical conditions, vaccination is especially important.

The OFHC Perspective

At Orleans Family Health Clinic, preventive care remains a cornerstone of healthy aging.

Our team works with patients to:

• Review vaccination status
• Assess chronic disease risks
• Recommend age-appropriate immunizations
• Support evidence-based preventive care decisions

For seniors, enhanced influenza vaccines represent an important tool in reducing the burden of seasonal respiratory illness and helping maintain independence and overall health.

Patients are encouraged to discuss influenza vaccination options with their healthcare provider each flu season.

Frequently Asked Questions

Is a high-dose flu shot better than Fluad?

Current evidence suggests both vaccines provide similar protection in adults aged 65 years and older.

Should seniors avoid standard-dose influenza vaccines?

Enhanced vaccines are generally preferred for older adults because they produce stronger immune responses.

Can seniors still get influenza after vaccination?

Yes. No vaccine is 100% effective. However, vaccination significantly reduces the risk of severe illness, hospitalization, and complications.

When should seniors get vaccinated?

Influenza vaccination is typically recommended annually in the fall before influenza season peaks.

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Disclaimer: The medical information on this site is provided as an information resource only and is not to be used or relied on for any diagnostic or treatment purposes. This information does not substitute for professional diagnosis and treatment. Please do not initiate, modify, or discontinue any treatment, medication, or supplement solely based on this information. Always seek the advice of your healthcare provider first. Full Disclaimer.