Recruiting
Phase 1

Fluzone® HD with CD388

Sponsor:

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

Code:

NCT07300085

Conditions

Healthy Participants

Eligibility Criteria

Sex: All

Age: 18 - 49

Healthy Volunteers: Accepted

Interventions

Fluzone® High-Dose (HD) influenza vaccine

MK-1406 Injection

Placebo

Study Details

Brief summary:

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®

Conditions

Healthy Participants

Study ID

NCT07300085

Start date

Nov 8, 2025

Status verified date

Nov, 2026

Completion date

Dec 31, 2026

Anticipated

Primary completion date

Dec 31, 2026

Anticipated

Eligibility Criteria

Eligibility Criteria

Sex: All

Age: 18 - 49

Healthy Volunteers: Accepted

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.

Study Design

Enrollment

710 participants

Anticipated

Allocation

Randomized

Intervention Model

Parallel Assignment

Primary purpose

Prevention

Interventions and Outcome Measures

Arms

experimental: Fluzone® High-Dose (HD) plus MK-1406

Participants will receive open-label Fluzone® HD influenza vaccine by intramuscular (IM) injection plus MK-1406 by subcutaneous (SC) injection on Day 1.

placebo comparator: Fluzone® HD plus Placebo

Participants will receive open-label Fluzone® HD influenza vaccine by IM injection plus placebo by SC injection on Day 1.

Interventions

Fluzone® High-Dose (HD) influenza vaccine

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

MK-1406 Injection

MK-1406 liquid for injection administered subcutaneously

Placebo

MK-1406 matched liquid for SC injection

Primary outcome measure

  • 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 ]
  • 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 ]

Central Contacts and Locations

Central contacts

Toll Free Number

1-888-577-8839Trialsites@msd.com

Locations

Parexel ( Site 0001)

Recruiting

Glendale, California, United States, 91206

Contacts

Study Coordinator

888-228-7425

Parexel ( Site 0002)

Recruiting

Baltimore, Maryland, United States, 21225

Contacts

Study Coordinator

410-350-3200

More Information

Sponsor

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

Last update posted

Nov 4, 2026

Last verified

Nov, 2026

Keywords

  • Influenza
  • Antiviral Agents

Trial information was received from ClinicalTrials.gov and was last updated on 2026-11-05. This information was provided to ClinicalTrials.gov by Cidara Therapeutics Inc., a subsidiary of Merck & Co., Inc. (Rahway, New Jersey USA) on 2026-11-04. Recruitment status is synced daily from ClinicalTrials.gov and may not reflect the sponsor's current status. Confirm during your call.