HealthyPhase 2NCT05903183

A Study to Evaluate the Safety and Immunogenicity of IVX-A12 in Participants of 60 to 85 Years of Age

A Phase 2 study testing IVX-A12 in people with Healthy, run by Icosavax, Inc. at 10 sites in United States.

Completed

Finished. The study has ended and is not enrolling. Results may be posted on the official record.

Trial summary

The primary purpose of the study is to assess the safety, tolerability and immunogenicity of a bivalent respiratory syncytial virus (RSV)/human metapneumovirus (hMPV) virus-like particle (VLP) candidate vaccine (IVX-A12) compared to placebo, when administered as a single-dose regimen in healthy older adults 60 to 85… Read more about this study

Who is it for?: Ages 60 to 85 yearsHealthy volunteers can take part
Conditions the study is for: Healthy
What is being tested?: IVX-A12
Type of treatment: Injection or infusion
Could I receive a placebo?: Yes, some participants may receive a placebo
How many people: 264 participants
Where: 10 sitesUnited States
Study dates: 15 May 2023to 25 Oct 2024
Phase: Phase 2
Are there results?: Yes, posted in the registrySummary in the doctors' view

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 60 to 85 years
All sexes
Healthy volunteers accepted
Adult, Older adult

Who may be able to join

Male or female participants, who must be in stable health based on medical history, vital signs, physical examination, and laboratory evaluation prior to vaccination, in the investigator's clinical judgment
Participants may have ongoing chronic conditions (comorbidities such as hypertension, congestive heart failure, chronic obstructive pulmonary disease, type 2 diabetes mellitus, hyperlipoproteinemia, or hypothyroidism) who are, in the investigator's opinion, medically compensated and without recent exacerbation within the prior 3 months
Participants able to voluntarily give written informed consent and can comply with trial procedures including follow-up for approximately 12 months after vaccination
Body mass index 17 to less than (<) 40 kilograms per square meter (kg/m^2) at screening
Before randomization, female participants must be unable to conceive (example, menopausal, that is, 12 consecutive months without menstruation, hysterectomy, oophorectomy, etc.) and not intending to conceive by any method
Participants must agree not to donate blood from the time of vaccination through 3 months after vaccination
Participants must be willing to provide verifiable identification and have the means to be contacted and to contact the investigator or the site's staff during the entire clinical trial

Who cannot join

Participants with moderate or severe liver disease, metastatic solid tumor, and acquired immunodeficiency syndrome (AIDS) are to be excluded. In addition, participants with underlying significant illness or condition(s) or ongoing treatment that, in the opinion of the investigator, could (i) interfere with the conduct of the trial, (ii) pose an unacceptable risk to the participant in this trial, (iii) interfere with the participant's ability to comply with the trial procedures or abide by the procedures
Older adults who meet frail elderly criteria (older persons with medical, nutritional, cognitive, emotional, or activity impairments, as defined by the Dalhousie Clinical Frailty Score greater than or equal to [>=]4)
Prior receipt of any licensed or investigational RSV or hMPV vaccine within the past 12 months
Prior receipt of another investigational medicinal product (IMP; trial drug, biologic, or device) not authorized for use in the United States of America (USA) and European Union within the past 3 months
Laboratory-confirmed RSV or hMPV infection within 12 months prior to enrollment
Currently enrolled or plan to participate in another clinical trial with an investigational agent (including licensed or unlicensed vaccine, drug, biologic, device, blood product, or medication) to be received during the trial period

Show all 16Show fewer

History of malignancy within 5 years before screening not in the following categories: (i) participants with squamous and basal cell carcinomas of the skin and carcinoma in situ of the cervix may be enrolled at the discretion of the investigator, (ii) participants with a history of malignancy within 5 years before screening, with minimal risk of recurrence per investigator's judgment, can be enrolled
Acute illness, with or without fever at the time of planned vaccination
History of hypersensitivity or serious adverse reactions to vaccines, such as anaphylaxis or angioedema, or any known allergies to any component of the IVX-121 and/or IVX-241 vaccine, or hypersensitivity to latex
Abnormal function of the immune system resulting from clinical conditions including chronic administration of systemic corticosteroids (oral/intravenous/IM at a daily dose equivalent of greater than (>) 20 milligram (mg) prednisone in a period of more than 14 days), or administration of immunosuppressive chemotherapy, biologics, or radiotherapy within the past 3 months prior to planned vaccination
Participants who have received treatment with immunoglobulins or other biologics, such as immunosuppressive therapies expected to modify immune response to vaccination (including monoclonal antibodies [MAbs] for chronic underlying conditions) within the past 3 months prior to planned vaccination
Trial personnel as an immediate family or household member
For licensed vaccines:
Receipt of licensed inactivated vaccines (including seasonal influenza vaccine) within 14 days prior to trial vaccine administration on Day 0, or licensed replicating vaccines such as ribonucleic acid (RNA) or live-attenuated virus vaccines within 30 days prior to Day 0
Receipt of licensed vaccines is permitted after completion of the Day 28 visit
Receipt of any licensed Coronavirus Disease-2019 (COVID-19) vaccines is permitted if dosing regimen completed within 21 days prior to Day 0 or after completion of the Day 28 visit.

Trial locations and contacts

10 sites in 1 country.

City, postcode or hospital

10 sites in 1 country

United States10 sites

PanAmerican Clinical Research
Brownsville, Texas, 78520
Cenexel RCA
Hollywood, Florida, 33024
Johnson City Clin-Trials (JCCT)
Lenexa, Kansas, 66219
AMR Lexington
Lexington, Kentucky, 40509
Velocity Clinical Research-Boise
Meridian, Idaho, 83642
ASR, LLC
Nampa, Idaho, 83587
Velocity Clinical Research
Omaha, Nebraska, 68134
Rochester Clinical Research, Inc
Rochester, New York, 14609
Clinical Research Atlanta
Stockbridge, Georgia, 30281
AMR Phoenix
Tempe, Arizona, 85281

Other trials in United States

About this study

Official title: A Phase 2a Randomized, Observer-blind, Placebo-controlled, Dosage Optimization, Multi-center Clinical Trial to Evaluate the Safety and Immunogenicity of IVX-A12, a Respiratory Syncytial Virus and Human Metapneumovirus Bivalent Combination Virus-like Particle Protein Subunit Vaccine, in Adults 60 to 85 Years of Age

Read the detailed description

The IVX-A12 Phase 2a clinical trial is a randomized, observer-blind, placebo-controlled, dosage optimization, multi-center trial to evaluate the safety and immunogenicity of a single intramuscular (IM) dose of IVX-A12, with or without adjuvant, in adults 60 to 85 years of age.

Participants will be administered a single shot of IVX-A12, at specified dosage levels, or placebo. The overall duration of the study is up to 1 year (12 months). A subset of participants will be followed for an additional 12 months for a total duration of 24 months.

Conditions: Healthy
Being tested: IVX-A12, Placebo
Keywords: Respiratory syncytial virus (RSV), Human metapneumovirus (hMPV), Bivalent virus-like particle protein subunit vaccine

What participants receive

What participants receive. In a randomised study each person is assigned to one group by chance.

IVX-A12Biological
IVX-A12 without adjuvant
IVX-A12Biological
IVX-A12 with adjuvant
PlaceboBiological
Diluent

Study groups in NCT05903183
Study group	Role	What they receive
IVX-A12 Vaccine Formulation 1	Experimental	Participants will receive a single dose of IVX-A12 intramuscular (IM) injection on Day 0. Receives: Biological: IVX-A12
IVX-A12 Vaccine Formulation 2	Experimental	Participants will receive a single dose of IVX-A12 IM injection on Day 0. Receives: Biological: IVX-A12
Placebo	Placebo comparator	Participants will receive a single dose of placebo IM injection on Day 0. Receives: Biological: Placebo

What is being measured

The primary outcome is the main question the study is designed to answer.

Number of Participants With Solicited Local Adverse Reactions (ARs) and Systemic ARs
Solicited local ARs include pain, tenderness, erythema, and swelling. Solicited systemic ARs include headache, chills, fatigue, myalgia, arthralgia, vomiting, diarrhea, and fever.
Measured: From Day 0 to Day 6
Number of Participants With Unsolicited Adverse Events
An unsolicited AE is an AE that was not solicited using the post-vaccination diary and that was spontaneously communicated by a participant.
Measured: From Day 0 to Day 28
Model-adjusted Geometric Mean Titers (GMT) for RSV-A, RSV-B, hMPV-A, and hMPV-B-specific Neutralizing Antibodies (NAb)
Model-adjusted GMT and corresponding 95% CI were derived from an analysis of covariance (ANCOVA) model of log2 titer at Day 28 with independent variables of log2 baseline titer, age group, and treatment group.
Measured: At Day 28
Model-adjusted Geometric Mean Concentrations (GMC) for RSV and hMPV Prefusion F Protein-specific IgG Antibodies (Ab)
Model-adjusted GMC and corresponding 95% CI were derived from an analysis of covariance (ANCOVA) model of log2 concentration at Day 28 with independent variables of log2 baseline concentration, age group, and treatment group.
Measured: At Day 28
Percentage of Participants With a >=4-fold Increase in Serum RSV-A, RSV-B, hMPV-A, and hMPV-B-specific NAb Titers
Proportion of participants with non-missing results at the specified visit achieving a 4-fold or greater increase in NAb titer versus baseline (Day 0).
Measured: From Day 0 (pre-vaccination) up to Day 28 post-vaccination
Percentage of Participants With >=4-fold Increase in RSV and hMPV-specific IgG Ab Concentration
Proportion of participants with non-missing results at the specified visit achieving a 4-fold or greater increase in Ab concentration versus baseline (Day 0).
Measured: From Day 0 (pre-vaccination) up to Day 28 post-vaccination
Geometric Mean Fold Rise (GMFR) in Serum for RSV-A, RSV-B, hMPV-A, and hMPV-B-Specific NAb Titers
GMFR is defined as the geometric mean of the ratio of NAb titer at specified timepoints after vaccination divided by baseline (Day 0) titer.
Measured: From Day 0 (pre-vaccination) up to Day 28 post-vaccination
Geometric Mean Fold Rise (GMFR) in Serum for RSV and hMPV Prefusion F Protein-specific IgG Ab Concentrations
GMFR is defined as the geometric mean of the ratio of Ab concentration at specified timepoints after vaccination divided by baseline (Day 0) concentration.
Measured: From Day 0 (pre-vaccination) up to Day 28 post-vaccination

Secondary outcomes (11)

Number of Participants With Serious Adverse Event (SAE), Medically-attended Adverse Events (MAAEs), and AEs Leading to Trial Withdrawal
An SAE is defined as any untoward medical occurrence that met one or more of the following: resulted in death; was immediately life-threatening; required in-patient hospitalization or prolongation of existing hospitalization; resulted in persistent or significant disability/incapacity; was a congenital anomaly or birth defect in the offspring of a subject; was an important and significant medical event that might have jeopardized the participant or required medical intervention to prevent one of the aforementioned outcomes. Any AESI occurring during the trial will be categorized and reported as an SAE. These AESIs include anaphylaxis, thrombocytopenia, and other potential immune-mediate conditions (including Guillain Barre syndrome). MAAEs are defined as AEs leading to an unscheduled visit to or by a healthcare professional, including visits to an emergency department, but not fulfilling seriousness criteria.
Measured: From Day 0 up to the end of study (up to Day 365)
Number of Participants With Mild, Moderate, or Severe Lower Respiratory Tract Illness (LRTI) Caused by RSV and/or hMPV
Data is summarized as the number of subjects with at least one LRTI event (mild, moderate, or severe) by treatment group.
Measured: From Day 0 up to Day 365 (end of study)
Number of Participants With Mild, Moderate, or Severe LRTI Cases Not Caused by RSV or hMPV
Data is summarized as the number of subjects with at least one LRTI event (mild, moderate, or severe) by treatment group.
Measured: From Day 0 up to Day 365 (end of study)
Number of Participants With Clinically Significant Safety Laboratory Parameters
Measured: At Screening, Days 0, 7 and 28
Model-Adjusted GMTs for RSV-A, RSV-B, hMPV-A, and hMPV-B-specific NAb
Model-adjusted GMT and corresponding 95% CI were derived from an analysis of covariance (ANCOVA) model of log2 titer at each post-baseline timepoint with independent variables of log2 baseline titer, age group, and treatment group.
Measured: At Days 180 and 365
Model-Adjusted GMCs for RSV and hMPV Prefusion F Protein-specific IgG Ab Concentrations
Model-adjusted GMC and corresponding 95% CI were derived from an analysis of covariance (ANCOVA) model of log2 concentration at each post-baseline timepoint with independent variables of log2 baseline concentration, age group, and treatment group.
Measured: At Days 180, and 365
Percentage of Participants With a >=4-fold Increase in Serum RSV-A, RSV-B, hMPV-A, and hMPV-B-specific NAb Titers
Proportion of participants with non-missing results at the specified visit achieving a 4-fold or greater increase in NAb titer versus baseline (Day 0).
Measured: From Day 0 (pre-vaccination) up to Day 180 and Day 365 post-vaccination
Percentage of Participants With >=4-fold Increase in RSV and hMPV Prefusion F Protein-specific IgG Ab Concentrations
Proportion of participants with non-missing results at the specified visit achieving a 4-fold or greater increase in Ab concentration versus baseline (Day 0).
Measured: From Day 0 (pre-vaccination) up to Days 180, and 365 post-vaccination
Percentage of Participants With a >=8-fold Increase in Serum RSV-A, RSV-B, hMPV-A, and hMPV-B-specific NAb Titers
Proportion of participants with non-missing results at the specified visit achieving a 8-fold or greater increase in NAb titer versus baseline (Day 0).
Measured: From Day 0 (pre-vaccination) up to Days 28, 180, and 365 post-vaccination
GMFR in Serum for RSV-A, RSV-B, hMPV-A, and hMPV-B-specific NAb Titers and RSV and hMPV Prefusion F Protein-specific IgG Ab Concentrations
GMFR is defined as the geometric mean of the ratio of Ab concentration at specified timepoints after vaccination divided by baseline (Day 0) concentration.
Measured: From Day 0 (pre-vaccination) up to Day 180 and Day 365 post-vaccination
Reverse Cumulative Distribution (RCD) Curve of Serum NAb Titers and IgG Ab Concentrations
The median, as well as 25th and 75th percentiles of serum NAb titers and IgG Ab concentrations are summarized at specified timepoints.
Measured: At Days 28, 180, and 365 post-vaccination

Timeline

From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.

15 May 202325 Oct 2024

First posted15 Jun 2023
Study start15 May 2023
Primary completion5 Jun 2023
Study completion25 Oct 2024

Resources

Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
Posted resultsParticipant flow, outcome measures and adverse events reported by the sponsor.
Other trials for HealthyStudies 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 2
Primary purpose: Other
Allocation: Randomised
Intervention model: Parallel groups
Masking: Quadruple blind
Who is masked: Participant, Care provider, Investigator, Outcomes assessor
Enrolment: 264 participants (actual)

IDs, dates and publications

ClinicalTrials.gov ID: NCT05903183
Sponsor's protocol ID: ICVX-12-201
Status last verified: Nov 2025
First submitted: 5 Jun 2023
Last updated: 5 Dec 2025
Results posted: Yes, on ClinicalTrials.gov
Data monitoring committee: Yes
FDA-regulated drug: Yes
FDA-regulated device: No
Individual data sharing: No

Want to know more?

The sponsor has not listed a contact. The official record may have more details.

Talk to your doctor first and take this page with you. Only the study team can confirm whether you can join.

Questions to ask the study team

What is the study trying to find out?
What would I need to do, and how often would I visit?
Could I receive a placebo instead of the treatment?
What are the possible risks and benefits for me?
Will it cost me anything? Are travel or time paid for?
Can I keep seeing my own doctor during the study?
What happens when the study ends?

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Study at a glance

From the registry record, last updated by the sponsor on 5 Dec 2025. Recruitment status is as the sponsor reported it: confirm with the study team.

Official title: A Phase 2a Randomized, Observer-blind, Placebo-controlled, Dosage Optimization, Multi-center Clinical Trial to Evaluate the Safety and Immunogenicity of IVX-A12, a Respiratory Syncytial Virus and Human Metapneumovirus Bivalent Combination Virus-like Particle Protein Subunit Vaccine, in Adults 60 to 85 Years of Age
ClinicalTrials.gov ID: NCT05903183
Acronym / sponsor ID: ICVX-12-201
Conditions: Healthy
Keywords: Respiratory syncytial virus (RSV), Human metapneumovirus (hMPV), Bivalent virus-like particle protein subunit vaccine
Phase: Phase 2
Study type: Interventional
Recruitment status: Completed
Enrolment: 264 participants (actual)
Lead sponsor: Icosavax, Inc.Industry (pharma, biotech, devices)
Study start: 15 May 2023 (actual)
Primary completion: 5 Jun 2023 (actual)
Study completion: 25 Oct 2024 (actual)
First posted: 15 Jun 2023 (actual)
Results: Posted 5 Dec 2025

Clinical summary

The research question as the sponsor registered it. This describes what the study plans to test, not what it found.

Detailed description

Study design

Primary purpose: Other
Allocation: Randomised
Intervention model: Parallel groups
Masking: Quadruple blind (participant, care provider, investigator, outcomes assessor)
Number of arms: 3

Arm	Type	Receives
IVX-A12 Vaccine Formulation 1	Experimental	Biological: IVX-A12Participants will receive a single dose of IVX-A12 intramuscular (IM) injection on Day 0.
IVX-A12 Vaccine Formulation 2	Experimental	Biological: IVX-A12Participants will receive a single dose of IVX-A12 IM injection on Day 0.
Placebo	Placebo comparator	Biological: PlaceboParticipants will receive a single dose of placebo IM injection on Day 0.

Who may qualify

Ages: 60 to 85 years
Sex: All
Healthy volunteers: Accepted
Age groups: Adult, Older adult

Key inclusion criteria (7 listed)

Male or female participants, who must be in stable health based on medical history, vital signs, physical examination, and laboratory evaluation prior to vaccination, in the investigator's clinical judgment
Participants may have ongoing chronic conditions (comorbidities such as hypertension, congestive heart failure, chronic obstructive pulmonary disease, type 2 diabetes mellitus, hyperlipoproteinemia, or hypothyroidism) who are, in the investigator's opinion, medically compensated and without recent exacerbation within the prior 3 months
Participants able to voluntarily give written informed consent and can comply with trial procedures including follow-up for approximately 12 months after vaccination
Body mass index 17 to less than (<) 40 kilograms per square meter (kg/m^2) at screening
Before randomization, female participants must be unable to conceive (example, menopausal, that is, 12 consecutive months without menstruation, hysterectomy, oophorectomy, etc.) and not intending to conceive by any method

Key exclusion criteria (16 listed)

Participants with moderate or severe liver disease, metastatic solid tumor, and acquired immunodeficiency syndrome (AIDS) are to be excluded. In addition, participants with underlying significant illness or condition(s) or ongoing treatment that, in the opinion of the investigator, could (i) interfere with the conduct of the trial, (ii) pose an unacceptable risk to the participant in this trial, (iii) interfere with the participant's ability to comply with the trial procedures or abide by the procedures
Older adults who meet frail elderly criteria (older persons with medical, nutritional, cognitive, emotional, or activity impairments, as defined by the Dalhousie Clinical Frailty Score greater than or equal to [>=]4)
Prior receipt of any licensed or investigational RSV or hMPV vaccine within the past 12 months
Prior receipt of another investigational medicinal product (IMP; trial drug, biologic, or device) not authorized for use in the United States of America (USA) and European Union within the past 3 months
Laboratory-confirmed RSV or hMPV infection within 12 months prior to enrollment

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
IVX-A12IVX-A12 without adjuvant	Biological	IVX-A12 Vaccine Formulation 1
IVX-A12IVX-A12 with adjuvant	Biological	IVX-A12 Vaccine Formulation 2
PlaceboDiluent	Biological	Placebo

Primary outcome

Number of Participants With Solicited Local Adverse Reactions (ARs) and Systemic ARs
Time frame: From Day 0 to Day 6
Solicited local ARs include pain, tenderness, erythema, and swelling. Solicited systemic ARs include headache, chills, fatigue, myalgia, arthralgia, vomiting, diarrhea, and fever.
Number of Participants With Unsolicited Adverse Events
Time frame: From Day 0 to Day 28
An unsolicited AE is an AE that was not solicited using the post-vaccination diary and that was spontaneously communicated by a participant.
Model-adjusted Geometric Mean Titers (GMT) for RSV-A, RSV-B, hMPV-A, and hMPV-B-specific Neutralizing Antibodies (NAb)
Time frame: At Day 28
Model-adjusted GMT and corresponding 95% CI were derived from an analysis of covariance (ANCOVA) model of log2 titer at Day 28 with independent variables of log2 baseline titer, age group, and treatment group.
Model-adjusted Geometric Mean Concentrations (GMC) for RSV and hMPV Prefusion F Protein-specific IgG Antibodies (Ab)
Time frame: At Day 28
Model-adjusted GMC and corresponding 95% CI were derived from an analysis of covariance (ANCOVA) model of log2 concentration at Day 28 with independent variables of log2 baseline concentration, age group, and treatment group.
Percentage of Participants With a >=4-fold Increase in Serum RSV-A, RSV-B, hMPV-A, and hMPV-B-specific NAb Titers
Time frame: From Day 0 (pre-vaccination) up to Day 28 post-vaccination
Proportion of participants with non-missing results at the specified visit achieving a 4-fold or greater increase in NAb titer versus baseline (Day 0).
Percentage of Participants With >=4-fold Increase in RSV and hMPV-specific IgG Ab Concentration
Time frame: From Day 0 (pre-vaccination) up to Day 28 post-vaccination
Proportion of participants with non-missing results at the specified visit achieving a 4-fold or greater increase in Ab concentration versus baseline (Day 0).
Geometric Mean Fold Rise (GMFR) in Serum for RSV-A, RSV-B, hMPV-A, and hMPV-B-Specific NAb Titers
Time frame: From Day 0 (pre-vaccination) up to Day 28 post-vaccination
GMFR is defined as the geometric mean of the ratio of NAb titer at specified timepoints after vaccination divided by baseline (Day 0) titer.
Geometric Mean Fold Rise (GMFR) in Serum for RSV and hMPV Prefusion F Protein-specific IgG Ab Concentrations
Time frame: From Day 0 (pre-vaccination) up to Day 28 post-vaccination
GMFR is defined as the geometric mean of the ratio of Ab concentration at specified timepoints after vaccination divided by baseline (Day 0) concentration.

11 secondary outcomes

Number of Participants With Serious Adverse Event (SAE), Medically-attended Adverse Events (MAAEs), and AEs Leading to Trial Withdrawal
Time frame: From Day 0 up to the end of study (up to Day 365)
Number of Participants With Mild, Moderate, or Severe Lower Respiratory Tract Illness (LRTI) Caused by RSV and/or hMPV
Time frame: From Day 0 up to Day 365 (end of study)
Number of Participants With Mild, Moderate, or Severe LRTI Cases Not Caused by RSV or hMPV
Time frame: From Day 0 up to Day 365 (end of study)
Number of Participants With Clinically Significant Safety Laboratory Parameters
Time frame: At Screening, Days 0, 7 and 28
Model-Adjusted GMTs for RSV-A, RSV-B, hMPV-A, and hMPV-B-specific NAb
Time frame: At Days 180 and 365
Model-Adjusted GMCs for RSV and hMPV Prefusion F Protein-specific IgG Ab Concentrations
Time frame: At Days 180, and 365
Percentage of Participants With a >=4-fold Increase in Serum RSV-A, RSV-B, hMPV-A, and hMPV-B-specific NAb Titers
Time frame: From Day 0 (pre-vaccination) up to Day 180 and Day 365 post-vaccination
Percentage of Participants With >=4-fold Increase in RSV and hMPV Prefusion F Protein-specific IgG Ab Concentrations
Time frame: From Day 0 (pre-vaccination) up to Days 180, and 365 post-vaccination
Percentage of Participants With a >=8-fold Increase in Serum RSV-A, RSV-B, hMPV-A, and hMPV-B-specific NAb Titers
Time frame: From Day 0 (pre-vaccination) up to Days 28, 180, and 365 post-vaccination
GMFR in Serum for RSV-A, RSV-B, hMPV-A, and hMPV-B-specific NAb Titers and RSV and hMPV Prefusion F Protein-specific IgG Ab Concentrations
Time frame: From Day 0 (pre-vaccination) up to Day 180 and Day 365 post-vaccination
Reverse Cumulative Distribution (RCD) Curve of Serum NAb Titers and IgG Ab Concentrations
Time frame: At Days 28, 180, and 365 post-vaccination

Results and safety

Results posted to the registry on 5 Dec 2025, as reported by the sponsor. Figures are copied from the record, not re-analysed. Full results on ClinicalTrials.gov.

Participant flow

Group	Started	Completed
Main Trial Part: IVX-A12 150 mcg	102	99
Main Trial Part: IVX-A12 150 mcg With MF59	109	107
Main Trial Part: Placebo	53	51
Observational Extension Part: IVX-A12 150 mcg	0	0
Observational Extension Part: Placebo	0	0

Primary outcome: Number of Participants With Solicited Local Adverse Reactions (ARs) and Systemic ARs

Time frame: From Day 0 to Day 6. Count of participants. Unit: Participants

Measure	Main Trial Part: IVX-A12 150 mcg n = 103	Main Trial Part: IVX-A12 150 mcg With MF59 n = 108	Main Trial Part: Placebo n = 53
Solicited Local Adverse Reactions	46	68	5
Solicited Systemic Adverse Reactions	34	56	19

Population analysed: The Safety Set includes all participants who received any amount of IVX-A12 or placebo.

Primary outcome: Number of Participants With Unsolicited Adverse Events

Time frame: From Day 0 to Day 28. Count of participants. Unit: Participants

Measure	Main Trial Part: IVX-A12 150 mcg n = 103	Main Trial Part: IVX-A12 150 mcg With MF59 n = 108	Main Trial Part: Placebo n = 53
Value	33	38	13

Population analysed: The Safety Set includes all participants who received any amount of IVX-A12 or placebo.

Primary outcome: Model-adjusted Geometric Mean Titers (GMT) for RSV-A, RSV-B, hMPV-A, and hMPV-B-specific Neutralizing Antibodies (NAb)

Time frame: At Day 28. Geometric mean (95% Confidence Interval). Unit: MN50 titer

Measure	Main Trial Part: IVX-A12 150 mcg n = 96	Main Trial Part: IVX-A12 150 mcg With MF59 n = 98	Main Trial Part: Placebo n = 47
RSV-A	11980.96 (9760.34 to 14706.80)	11167.48 (9101.24 to 13702.82)	1944.00 (1449.07 to 2607.97)
RSV-B	7787.22 (6516.69 to 9305.46)	6560.64 (5493.69 to 7834.81)	2205.65 (1708.45 to 2847.55)
hMPV-A	1643.58 (1378.03 to 1960.31)	1416.79 (1187.96 to 1689.69)	465.09 (361.26 to 598.76)
hMPV-B	15503.09 (13515.07 to 17783.54)	17317.65 (15103.86 to 19855.92)	6370.00 (5230.31 to 7758.03)

Population analysed: The PPS includes all participants in the FAS who received a dose of IVX-A12 or placebo and have no major protocol deviations, which may exclude participants from PPS.

Primary outcome: Model-adjusted Geometric Mean Concentrations (GMC) for RSV and hMPV Prefusion F Protein-specific IgG Antibodies (Ab)

Time frame: At Day 28. Geometric mean (95% Confidence Interval). Unit: ELISA units per milliliter (EU/mL)

Measure	Main Trial Part: IVX-A12 150 mcg n = 96	Main Trial Part: IVX-A12 150 mcg With MF59 n = 98	Main Trial Part: Placebo n = 47
RSV	1549.06 (1369.32 to 1752.38)	1556.06 (1375.49 to 1760.33)	393.03 (329.37 to 468.99)
hMPV	1707.15 (1482.99 to 1965.19)	1856.88 (1614.14 to 2136.12)	444.74 (363.06 to 544.79)

Population analysed: The PPS includes all participants in the FAS who received a dose of IVX-A12 or placebo and have no major protocol deviations, which may exclude participants from PPS.

11 secondary outcomes are reported in the full results.

Adverse events

Time frame: From study start to end of observational extension part (up to Day 509). Other adverse events reported at 0% frequency or more

Group	Serious adverse events	Other adverse events	Deaths
Main Trial Part: IVX-A12 150 mcg	5 of 103 (4.9%)	75 of 103 (72.8%)	1 of 103
Main Trial Part: IVX-A12 150 mcg With MF59	3 of 108 (2.8%)	81 of 108 (75%)	0 of 108
Main Trial Part: Placebo	1 of 53 (1.9%)	42 of 53 (79.2%)	0 of 53
Observational Extension Part: IVX-A12 150 mcg	1 of 35 (2.9%)	3 of 35 (8.6%)	0 of 35
Observational Extension Part: Placebo	0 of 20 (0%)	1 of 20 (5%)	0 of 20

Loading the posted results from ClinicalTrials.gov…

Research links

Official record on ClinicalTrials.govLast updated by the sponsor 5 Dec 2025.
Posted resultsParticipant flow, baseline, all outcome measures and adverse events.
Redacted CSPLink provided by the sponsor.
Redacted SAPLink provided by the sponsor.
ICVX-12-201\_Redacted CSR\_synopsisLink provided by the sponsor.
Individual participant dataSharing planned: No

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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. This study is not recruiting at the moment.

The record lists no contact. Use the official record to reach the sponsor.

10 sites in 1 country: see every site and its status.

Questions about this trial

What is this clinical trial studying?

A Phase 2 study testing IVX-A12 in people with Healthy, run by Icosavax, Inc. at 10 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 7 inclusion and 16 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: finished, as of the sponsor's last update on 5 Dec 2025. Status can change between updates, so confirm with the study contact before making plans.

Where is the study taking place?

The record lists 10 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 2 studies give the treatment to a larger group to see whether it has the intended effect and to keep checking safety.

Not every study follows the same path, and some studies (observational studies, device studies) have no phase.

Are results available for this study?

Yes. Results are posted in the registry (first posted 5 Dec 2025). A summary is in the For doctors view, and the full results are on ClinicalTrials.gov.

How can a doctor refer a patient or contact the research team?

The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.

What does the primary outcome measure?

Number of Participants With Solicited Local Adverse Reactions (ARs) and Systemic ARs (time frame: From Day 0 to Day 6). The study lists 8 primary outcomes in all. It is what the study was designed to measure, not a finding.

Where can I read the original study information?

On the ClinicalTrials.gov record for NCT05903183.

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 5 Dec 2025.