Healthy ParticipantsPhase 1NCT07300085
A Trial to Evaluate the Effect of CD388/MK1406 on the Immunogenicity of Fluzone® HD Vaccine (CD388.SQ.1.08/MK-1406-007)
A Phase 1 study testing Fluzone® High-Dose (HD) influenza vaccine and MK-1406 Injection in people with Healthy Participants, run by Cidara Therapeutics Inc., a subsidiary of Merck & Co., Inc. (Rahway, New Jersey USA) at 2 sites in United States.
Trial 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. Read more about this study
- Who is it for?
- Ages 18 to 49 yearsHealthy volunteers can take part
- Conditions the study is for
- Healthy Participants
- What is being tested?
- Fluzone® High-Dose (HD) influenza vaccine and MK-1406 Injection
- Type of treatment
- Vaccines, Injection or infusion
- Could I receive a placebo?
- Yes, some participants may receive a placebo
- How many people
- 710 participants
- Where
- 2 sitesUnited States
- Study dates
- 8 Nov 2025to 31 Dec 2026
- Phase
- Phase 1
- Are there results?
- Not yet: the study is under way
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 18 to 49 years
- All sexes
- Healthy volunteers accepted
- Adult
Who may be able to join
- 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
Who cannot join
- 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.
Trial locations and contacts
2 sites in 1 country. Contact the study team or a site near you to ask about taking part.
United States2 sites, 2 recruiting
- Recruiting
Parexel ( Site 0002)
Baltimore, Maryland, 21225
Study Coordinator, 410-350-3200
- Recruiting
Parexel ( Site 0001)
Glendale, California, 91206
Study Coordinator, 888-228-7425
About this study
Official 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
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®
Read the detailed description
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.
- Conditions
- Healthy Participants
- Being tested
- Fluzone® High-Dose (HD) influenza vaccine, MK-1406 Injection, Placebo
- Keywords
- Influenza, Antiviral Agents
- Medical subject headings
- Influenza, Human
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
Fluzone® High-Dose (HD) influenza vaccineBiological
Also called Fluzone® High-Dose Influenza Vaccine
Fluzone® HD injectable suspension administered by intramuscular (IM) injection
MK-1406 InjectionCombination product
Also called CD388
MK-1406 liquid for injection administered subcutaneously
PlaceboCombination product
MK-1406 matched liquid for SC injection
| Study group | Role | What they receive |
|---|---|---|
| Fluzone® High-Dose (HD) plus MK-1406 | Experimental | Participants will receive open-label Fluzone® HD influenza vaccine by intramuscular (IM) injection plus MK-1406 by subcutaneous (SC) injection on Day 1. Receives: Biological: Fluzone® High-Dose (HD) influenza vaccine; Combination Product: MK-1406 Injection |
| Fluzone® HD plus Placebo | Placebo comparator | Participants will receive open-label Fluzone® HD influenza vaccine by IM injection plus placebo by SC injection on Day 1. Receives: Biological: Fluzone® High-Dose (HD) influenza vaccine; Combination Product: Placebo |
What is being measured
The primary outcome is the main question the study is designed to answer.
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
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.
Measured: 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
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.
Measured: Predose (Day 1), Day 15 and Day 29
Secondary outcomes (4)
Percentage of participants with ≥1 Adverse Event (AE)
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.
Measured: Up to approximately Day 29
Percentage of Participants Who Discontinued from the Study Due to an Adverse Event
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.
Measured: Up to approximately Day 29
Percentage of Participants with a Solicited Injection-site Adverse Event
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.
Measured: Up to approximately Day 8 post-dose
Percentage of Participants with a Solicited Systemic Adverse Event
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.
Measured: Up to approximately Day 29
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted23 Dec 2025
- Study start8 Nov 2025
- Primary completion31 Dec 2026 (estimated)
- Study completion31 Dec 2026 (estimated)
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for Healthy ParticipantsStudies of the same condition, open and under way.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase 1
- Primary purpose
- Prevention
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- Quadruple blind
- Who is masked
- Participant, Care provider, Investigator, Outcomes assessor
- Enrolment
- 710 participants (estimated)
Sponsor and investigators
- Lead sponsor
- Cidara Therapeutics Inc., a subsidiary of Merck & Co., Inc. (Rahway, New Jersey USA)
- Sponsor type
- Industry (pharma, biotech, devices)
- Responsible party
- Sponsor
- Investigators
- Medical Director, Study director, Merck Sharp & Dohme LLC
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07300085
- Sponsor's protocol ID
- 1406-007
- Other IDs
- CD388.SQ.1.08, MK-1406-007
- Status last verified
- Nov 2026
- First submitted
- 10 Dec 2025
- Last updated
- 4 Nov 2026
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- Yes
- FDA-regulated device
- No
- Individual data sharing
- Yes: https://trialstransparency.msdclinicaltrials.com/pdf/ProcedureAccessClinicalTrialData.pdf
Study at a glance
From the registry record, last updated by the sponsor on 4 Nov 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official 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
- ClinicalTrials.gov ID
- NCT07300085
- Acronym / sponsor ID
- 1406-007
- Conditions
- Healthy Participants
- Keywords
- Influenza, Antiviral Agents
- Phase
- Phase 1
- Study type
- Interventional
- Recruitment status
- Recruiting
- Enrolment
- 710 participants (estimated)
- Lead sponsor
- Cidara Therapeutics Inc., a subsidiary of Merck & Co., Inc. (Rahway, New Jersey USA)Industry (pharma, biotech, devices)
- Study start
- 8 Nov 2025 (actual)
- Primary completion
- 31 Dec 2026 (estimated)
- Study completion
- 31 Dec 2026 (estimated)
- First posted
- 23 Dec 2025 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
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®
Detailed description
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.
Study design
- Primary purpose
- Prevention
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- Quadruple blind (participant, care provider, investigator, outcomes assessor)
- Number of arms
- 2
| Arm | Type | Receives |
|---|---|---|
| Fluzone® High-Dose (HD) plus MK-1406 | Experimental | Biological: Fluzone® High-Dose (HD) influenza vaccine, Combination Product: MK-1406 InjectionParticipants will receive open-label Fluzone® HD influenza vaccine by intramuscular (IM) injection plus MK-1406 by subcutaneous (SC) injection on Day 1. |
| Fluzone® HD plus Placebo | Placebo comparator | Biological: Fluzone® High-Dose (HD) influenza vaccine, Combination Product: PlaceboParticipants will receive open-label Fluzone® HD influenza vaccine by IM injection plus placebo by SC injection on Day 1. |
Who may qualify
- Ages
- 18 to 49 years
- Sex
- All
- Healthy volunteers
- Accepted
- Age groups
- Adult
Key inclusion criteria (4 listed)
- 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
Key exclusion criteria (3 listed)
- 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.
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| Fluzone® High-Dose (HD) influenza vaccineAlso: Fluzone® High-Dose Influenza VaccineFluzone® HD injectable suspension administered by intramuscular (IM) injection | Biological | Fluzone® HD plus Placebo, Fluzone® High-Dose (HD) plus MK-1406 |
| MK-1406 InjectionAlso: CD388MK-1406 liquid for injection administered subcutaneously | Combination product | Fluzone® High-Dose (HD) plus MK-1406 |
| PlaceboMK-1406 matched liquid for SC injection | Combination product | Fluzone® HD plus Placebo |
Primary outcome
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.
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.
4 secondary outcomes
Percentage of participants with ≥1 Adverse Event (AE)
Time frame: Up to approximately Day 29
Percentage of Participants Who Discontinued from the Study Due to an Adverse Event
Time frame: Up to approximately Day 29
Percentage of Participants with a Solicited Injection-site Adverse Event
Time frame: Up to approximately Day 8 post-dose
Percentage of Participants with a Solicited Systemic Adverse Event
Time frame: Up to approximately Day 29
Results and safety
This study is still under way. Results are not available in the source record yet.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 4 Nov 2026.
- Merck Clinical Trials InformationLink provided by the sponsor.
- Individual participant dataSharing planned: Yes. https://trialstransparency.msdclinicaltrials.com/pdf/ProcedureAccessClinicalTrialData.pdf
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Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part.
Medical Director study director
Merck Sharp & Dohme LLC
2 sites in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A Phase 1 study testing Fluzone® High-Dose (HD) influenza vaccine and MK-1406 Injection in people with Healthy Participants, run by Cidara Therapeutics Inc., a subsidiary of Merck & Co., Inc. (Rahway, New Jersey USA) at 2 sites in United States.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 4 inclusion and 3 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: looking for participants now, as of the sponsor's last update on 4 Nov 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 2 sites in United States. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. Some participants in this study may receive a placebo. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
What does this phase mean?
Phase 1 studies test a treatment in a small group of people for the first time or in a new way, mainly to check safety and find the right dose.
Not every study follows the same path, and some studies (observational studies, device studies) have no phase.
Are results available for this study?
This study is still under way. Results are not available in the source record yet.
How can a doctor refer a patient or contact the research team?
Contact Toll Free Number (1-888-577-8839, Trialsites@msd.com), or a site near the patient. AzTrials does not enrol participants or take referrals.
What does the 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). The study lists 2 primary outcomes in all. It is what the study was designed to measure, not a finding.
Where can I read the original study information?
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 4 Nov 2026.