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OpenTrials
Active, not recruiting

NCT Number: NCT07300085

A Trial to Evaluate the Effect of CD388/MK1406 on the Immunogenicity of Fluzone® HD Vaccine (CD388.SQ.1.08/MK-1406-007)

Approximately one billion cases of seasonal influenza occur annually. Of these, 3 to 5 million illnesses are severe and responsible for up to 650,000 deaths per year (WHO 2025). Yearly administration of an influenza vaccine for the prevention of influenza is currently recommended. However, the real-world vaccine effectiveness varied from 10% to 60% in the general population across the years of 2004 to 2024, with effectiveness in most years below 50% (CDC 2025) and decreasing to as low as 5% in immunocompromised individuals (Hughes 2021). Researchers are looking for other ways to prevent severe illness from the influenza virus.

The goals of this study are to learn if:

* MK-1406 (formerly CD388) is safe to take with Fluzone® * MK-1406 affects the immune response to Fluzone®

Active, not recruiting

This study is active but is not currently recruiting participants.

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Key information

Conditions

Healthy Participants Infections Influenza, Human Orthomyxoviridae Infections RNA Virus Infections Respiratory Tract Diseases Respiratory Tract Infections Virus Diseases

Age range

18 year–49 year

Sex eligibility

All sexes

Study type

Interventional

Phase

Phase 1

Primary location

California Clinical Trials Medical Group (CCTMG) managed by Parexel, Glendale, California, United States

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About this study

This is a Phase 1, double-blind, randomized trial to evaluate the immunogenicity of Fluzone® HD influenza vaccine when concomitantly administered with either MK-1406 or placebo, in healthy participants. This study will also evaluate the safety and tolerability of MK-1406 when administered with Fluzone® High-Dose (HD) compared to Fluzone® HD with placebo.

Who can participate

Healthy volunteers accepted: Yes

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

Inclusion criteria

The main inclusion criteria include but are not limited to the following:

  • Be ≥18 to ≤49 years of age
  • Be deemed healthy by the Investigator
  • Have not received any seasonal influenza vaccine and have not had a diagnosed or suspected influenza infection within 12 months prior to Day 1 of the trial

Exclusion criteria

The main exclusion criteria include but are not limited to the following:

  • Had an active malignancy within 5 years prior to screening, except basal cell or squamous cell skin cancer. Any history of breast cancer or melanoma is exclusionary.
  • Has previously been diagnosed with Guillain-Barre Syndrome following a previous influenza vaccination.

Treatment and study plan

Fluzone® High-Dose (HD) influenza vaccine

Biological

Fluzone® HD injectable suspension administered by intramuscular (IM) injection

Other names: Fluzone® High-Dose Influenza Vaccine

MK-1406 Injection

Combination Product

MK-1406 liquid for injection administered subcutaneously

Other names: CD388

Placebo

Combination Product

MK-1406 matched liquid for SC injection

Primary outcomes

  1. Geometric Mean of Hemagglutinin Inhibition (HAI) Titers Against the Influenza Strains Contained in the Vaccine Among Participants Receiving Concomitant Fluzone® High-Dose (HD) and MK-1406 Compared to Participants Who Receive Fluzone® HD and Placebo

    Time frame: Predose (Day 1), Day 15 and Day 29

    Geometric mean of HAI titers at 2-weeks and 4-weeks post-trial intervention against the influenza virus strains contained in the vaccine among participants receiving concomitant Fluzone® HD influenza vaccine and MK-1406 compared to participants who receive Fluzone® HD and placebo will be determined. HAI testing will be performed using validated methods in accordance with applicable Good Clinical Laboratory Practice (GCLP) and laboratory Standard Operating Procedures (SOPs). Geometric Mean Titers (GMTs) will be summarized by treatment group and influenza strain.

  2. Percentage of Participants with Seroconversion Rates against the Influenza Strains Contained in the Vaccine Among Participants Receiving Concomitant Fluzone® HD and MK-1406 Compared to Participants Who Receive Fluzone® HD and Placebo

    Time frame: Predose (Day 1), Day 15 and Day 29

    Seroconversion is defined as a 4-fold increase in influenza titer as measured by HAI assay at each visit compared to baseline. Seroconversion rates at 2-weeks and 4-weeks post-trial intervention against the influenza virus strains contained in the vaccine among participants receiving concomitant Fluzone® HD influenza vaccine and MK-1406 compared to participants who receive Fluzone® HD and placebo will be determined. Seroconversion rates will be summarized by treatment group and influenza strain.

Secondary outcomes

  1. Percentage of participants with ≥1 Adverse Event (AE)

    Time frame: Up to approximately Day 29

    An AE is defined as any untoward medical occurrence in a participant administered a pharmaceutical product temporally associated with the use of study treatment, whether or not considered related to the study treatment.

  2. Percentage of Participants Who Discontinued from the Study Due to an Adverse Event

    Time frame: Up to approximately Day 29

    An AE is defined as any untoward medical occurrence in a participant administered a pharmaceutical product temporally associated with the use of study treatment, whether or not considered related to the study treatment. The percentage of participants who discontinued the study because of an AE (as defined above) will be assessed.

  3. Percentage of Participants with a Solicited Injection-site Adverse Event

    Time frame: Up to approximately Day 8 post-dose

    An AE is any untoward medical occurrence in a patient or clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. The solicited injection-site AEs assessed are redness/erythema, swelling, and tenderness/pain.

  4. Percentage of Participants with a Solicited Systemic Adverse Event

    Time frame: Up to approximately Day 29

    An AE is any untoward medical occurrence in a patient or clinical study participant, temporally associated with the use of study treatment, whether or not considered related to the study treatment. The solicited systemic AEs assessed are muscle pain/myalgia, joint pain/arthralgia, headache, and tiredness/fatigue.

Sponsors and collaborators

Lead sponsor

Cidara Therapeutics Inc., a subsidiary of Merck & Co., Inc. (Rahway, New Jersey USA)

Industry

Registry information

Official study title

A Phase 1, Double-blind, Randomized Trial to Evaluate Safety and Immunogenicity of Fluzone® High-Dose Influenza Vaccine When Concomitantly Administered With CD388, a Novel Long-Acting Antiviral Conjugate for the Prevention of Influenza

Important dates

Study start
2025
Primary completion
2026
Study completion
2026
First posted
Dec 23, 2025
Registry last updated
Aug 19, 2026

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

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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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