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OpenTrials
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NCT Number: NCT07805837

Comparative Immunologic Mechanisms and Microbiome Interactions Following Different Influenza Vaccine Formulations in Older Adults

This prospective, randomized, open-label clinical study aims to evaluate the immunogenicity and underlying immune mechanisms of different influenza vaccine formulations in adults aged ≥65 years. Additionally, the study investigates the role of the gut microbiome in modulating vaccine-induced immune responses and durability.

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Key information

Conditions

Influenza Immune Response Infections Influenza Vaccines Influenza, Human Microbiome Orthomyxoviridae Infections RNA Virus Infections Respiratory Tract Diseases Respiratory Tract Infections Virus Diseases

Age range

65 year and older

Sex eligibility

All sexes

Study type

Interventional

Phase

Phase 4

Primary location

Korea University Guro Hospital

Seoul, 08308, South Korea

About this study

Despite high influenza vaccination coverage among older adults in Korea, vaccine effectiveness remains suboptimal, even during well-matched seasons. Immunosenescence and microbiome dysbiosis are believed to contribute to reduced vaccine responsiveness.

This study will:

  • Compare immune responses induced by standard-dose, MF59-adjuvanted, and high-dose influenza vaccines
  • Characterize cellular and humoral immune mechanisms
  • Analyze gut microbiome composition and function using metagenomic approaches
  • Identify microbiome-derived biomarkers associated with vaccine responsiveness and durability

Who can participate

Healthy volunteers accepted: Yes

Only the study team can determine whether someone qualifies for participation.

Inclusion criteria

  • Age ≥65 years
  • Able and willing to provide informed consent

Exclusion criteria

  • Influenza vaccination within the past 6 months
  • Laboratory-confirmed influenza infection within the past 6 months
  • Immunocompromised status
  • Uncontrolled chronic medical conditions

Treatment and study plan

Standard-Dose Influenza Vaccine

Biological

0.5 mL intramuscular injection, single dose

MF59-adjuvanted influenza vaccine

Biological

0.5 mL intramuscular injection, single dose

High-Dose Influenza Vaccine

Biological

0.7 mL intramuscular injection, single dose

Primary outcomes

  1. Seroconversion Rate

    Time frame: 4 weeks post-vaccination

    ≥4-fold increase in hemagglutination inhibition (HI) antibody titers

Secondary outcomes

  1. Geometric Mean Titers

    Time frame: Baseline, Day 7, Week 4, Month 6

    Geometric Mean Titers (GMTs) of HI antibodies

  2. Cellular Immune Responses

    Time frame: Baseline, Day 7, Week 4

    ELISpot (IFN-γ), activated T-cell frequency (CD38, HLA-DR)

  3. B Cell Responses

    Time frame: Baseline, Day 7, Week 4

    HA-specific B cell frequencies (A/H1N1, A/H3N2, B strains)

  4. Microbiome Diversity and Composition

    Time frame: Baseline and Week 4

    Alpha diversity (Shannon index) Beta diversity (PERMANOVA)

  5. Microbiome Biomarker Identification

    Time frame: Baseline, Week 4

    Taxonomic and functional markers using LEfSe analysis

  6. Durability of Immune Response

    Time frame: Baseline, Week 4, Month 6

    Antibody decay rate (half-life analysis)

  7. Safety Outcomes

    Time frame: Day 7, Day 30

    Solicited adverse events (within 7 days) Unsolicited adverse events (within 30 days)

Sponsors and collaborators

Lead sponsor

Korea University Guro Hospital

Other

Registry information

Important dates

Study start
2025
Primary completion
2026
Study completion
2026
First posted
Sep 4, 2026
Registry last updated
Sep 4, 2026

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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