CClinicalTrials.gg
Sign In
CompletedNCT05903183Updated Dec 5, 2025Results posted

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

A Phase 2 interventional study of IVX-A12 and IVX-A12 in Healthy, sponsored by Icosavax, Inc.. Completed at 10 sites in United States. Open to participants aged 60 Years to 85 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2025-12-05.

Sponsored by Icosavax, Inc. · Phase 2, Interventional, and Other

Phase
Phase 2
Study type
Interventional
Enrollment
264
Allocation
Randomized
Ages
60 Years to 85 Years
Sex
All
01

Study 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 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.

02

Conditions studied

  • Healthy

Keywords

  • Respiratory syncytial virus (RSV)
  • Human metapneumovirus (hMPV)
  • Bivalent virus-like particle protein subunit vaccine
03

In context

Lead sponsor

Icosavax, Inc. is the lead sponsor of 3 studies on the registry; none are open to participants now.

Counted across the registry records on this site, refreshed daily.

04

Who can participate

Ages eligible
60 Years to 85 Years
Sexes eligible
All
Accepts healthy volunteers
Yes

Inclusion criteria

  1. 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
  2. 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
  3. Participants able to voluntarily give written informed consent and can comply with trial procedures including follow-up for approximately 12 months after vaccination
  4. Body mass index 17 to less than (\<) 40 kilograms per square meter (kg/m\^2) at screening
  5. 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
  6. Participants must agree not to donate blood from the time of vaccination through 3 months after vaccination
  7. 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

Exclusion criteria

Exclusion Criteria:

  1. 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
  2. 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)
  3. Prior receipt of any licensed or investigational RSV or hMPV vaccine within the past 12 months
  4. 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
  5. Laboratory-confirmed RSV or hMPV infection within 12 months prior to enrollment
  6. 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
  7. 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
  8. Acute illness, with or without fever at the time of planned vaccination
  9. 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
  10. 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
  11. 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
  12. Trial personnel as an immediate family or household member

  13. For licensed vaccines:

    1. 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
    2. Receipt of licensed vaccines is permitted after completion of the Day 28 visit
    3. 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.
05

Study design

Phase
Phase 2
Primary purpose
Other
Allocation
Randomized
Intervention model
Parallel assignment
Masking
Quadruple (Participant, Care provider, Investigator, Outcomes assessor)
Enrollment
264 participants (actual)

Study arms

  • Experimental
    IVX-A12 Vaccine Formulation 1

    Participants will receive a single dose of IVX-A12 intramuscular (IM) injection on Day 0.

    Biological: IVX-A12

  • Experimental
    IVX-A12 Vaccine Formulation 2

    Participants will receive a single dose of IVX-A12 IM injection on Day 0.

    Biological: IVX-A12

  • Placebo comparator
    Placebo

    Participants will receive a single dose of placebo IM injection on Day 0.

    Biological: Placebo

Interventions

  • BiologicalIVX-A12

    IVX-A12 without adjuvant

  • BiologicalIVX-A12

    IVX-A12 with adjuvant

  • BiologicalPlacebo

    Diluent

06

What researchers measure

Primary outcomes

  1. 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.

    Time frame: From Day 0 to Day 6

  2. 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.

    Time frame: From Day 0 to Day 28

  3. 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.

    Time frame: At Day 28

  4. 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.

    Time frame: At Day 28

  5. 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).

    Time frame: From Day 0 (pre-vaccination) up to Day 28 post-vaccination

  6. 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).

    Time frame: From Day 0 (pre-vaccination) up to Day 28 post-vaccination

  7. 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.

    Time frame: From Day 0 (pre-vaccination) up to Day 28 post-vaccination

  8. 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.

    Time frame: From Day 0 (pre-vaccination) up to Day 28 post-vaccination

Secondary outcomes

  1. 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.

    Time frame: From Day 0 up to the end of study (up to Day 365)

  2. 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.

    Time frame: From Day 0 up to Day 365 (end of study)

  3. 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.

    Time frame: From Day 0 up to Day 365 (end of study)

  4. Number of Participants With Clinically Significant Safety Laboratory Parameters

    Time frame: At Screening, Days 0, 7 and 28

  5. 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.

    Time frame: At Days 180 and 365

  6. 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.

    Time frame: At Days 180, and 365

  7. 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).

    Time frame: From Day 0 (pre-vaccination) up to Day 180 and Day 365 post-vaccination

  8. 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).

    Time frame: From Day 0 (pre-vaccination) up to Days 180, and 365 post-vaccination

  9. 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).

    Time frame: From Day 0 (pre-vaccination) up to Days 28, 180, and 365 post-vaccination

  10. 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.

    Time frame: From Day 0 (pre-vaccination) up to Day 180 and Day 365 post-vaccination

  11. 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.

    Time frame: At Days 28, 180, and 365 post-vaccination

07

Results

Posted Dec 5, 2025

Participant flow

Participants were recruited at 10 investigative sites in the United States.

Main Trial Part (365 Days)
Participant flow — Main Trial Part (365 Days)
MilestoneMain Trial Part: IVX-A12 150 mcgMain Trial Part: IVX-A12 150 mcg With MF59Main Trial Part: PlaceboObservational Extension Part: IVX-A12 150 mcgObservational Extension Part: Placebo
Started1021095300
Safety set1031085300
Completed991075100
Not completed32200
Withdrew: Death10000
Withdrew: Other12100
Withdrew: Lost to follow-up00100
Withdrew: Withdrawal by subject10000
Observation Extension Part (144 Days)
Participant flow — Observation Extension Part (144 Days)
MilestoneMain Trial Part: IVX-A12 150 mcgMain Trial Part: IVX-A12 150 mcg With MF59Main Trial Part: PlaceboObservational Extension Part: IVX-A12 150 mcgObservational Extension Part: Placebo
Started0003520
Completed00000
Not completed0003520
Withdrew: Sponsor's decision0003520

Outcome measures

PrimaryNumber 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.

Time frame:
From Day 0 to Day 6
Reported as:
Count of participants · Participants
Number of Participants With Solicited Local Adverse Reactions (ARs) and Systemic ARs
ParticipantsMain Trial Part: IVX-A12 150 mcgMain Trial Part: IVX-A12 150 mcg With MF59Main Trial Part: Placebo
Solicited Local Adverse Reactions46685
Solicited Systemic Adverse Reactions345619
PrimaryNumber 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.

Time frame:
From Day 0 to Day 28
Reported as:
Count of participants · Participants
Number of Participants With Unsolicited Adverse Events
ParticipantsMain Trial Part: IVX-A12 150 mcgMain Trial Part: IVX-A12 150 mcg With MF59Main Trial Part: Placebo
Number of Participants With Unsolicited Adverse Events333813
PrimaryModel-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.

Time frame:
At Day 28
Reported as:
Geometric mean · MN50 titer
Model-adjusted Geometric Mean Titers (GMT) for RSV-A, RSV-B, hMPV-A, and hMPV-B-specific Neutralizing Antibodies (NAb)
MN50 titerMain Trial Part: IVX-A12 150 mcgMain Trial Part: IVX-A12 150 mcg With MF59Main Trial Part: Placebo
RSV-A11980.96 (9760.34 to 14706.80)11167.48 (9101.24 to 13702.82)1944.00 (1449.07 to 2607.97)
RSV-B7787.22 (6516.69 to 9305.46)6560.64 (5493.69 to 7834.81)2205.65 (1708.45 to 2847.55)
hMPV-A1643.58 (1378.03 to 1960.31)1416.79 (1187.96 to 1689.69)465.09 (361.26 to 598.76)
hMPV-B15503.09 (13515.07 to 17783.54)17317.65 (15103.86 to 19855.92)6370.00 (5230.31 to 7758.03)
PrimaryModel-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.

Time frame:
At Day 28
Reported as:
Geometric mean · ELISA units per milliliter (EU/mL)
Model-adjusted Geometric Mean Concentrations (GMC) for RSV and hMPV Prefusion F Protein-specific IgG Antibodies (Ab)
ELISA units per milliliter (EU/mL)Main Trial Part: IVX-A12 150 mcgMain Trial Part: IVX-A12 150 mcg With MF59Main Trial Part: Placebo
RSV1549.06 (1369.32 to 1752.38)1556.06 (1375.49 to 1760.33)393.03 (329.37 to 468.99)
hMPV1707.15 (1482.99 to 1965.19)1856.88 (1614.14 to 2136.12)444.74 (363.06 to 544.79)
PrimaryPercentage 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).

Time frame:
From Day 0 (pre-vaccination) up to Day 28 post-vaccination
Reported as:
Number · percentage of participants
Percentage of Participants With a >=4-fold Increase in Serum RSV-A, RSV-B, hMPV-A, and hMPV-B-specific NAb Titers
percentage of participantsMain Trial Part: IVX-A12 150 mcgMain Trial Part: IVX-A12 150 mcg With MF59Main Trial Part: Placebo
RSV-A: Day 2857.355.10
RSV-B: Day 2843.836.72.1
hMPV-A: Day 2838.528.60.0
hMPV-B: Day 2825.035.70
PrimaryPercentage 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).

Time frame:
From Day 0 (pre-vaccination) up to Day 28 post-vaccination
Reported as:
Number · percentage of participants
Percentage of Participants With >=4-fold Increase in RSV and hMPV-specific IgG Ab Concentration
percentage of participantsMain Trial Part: IVX-A12 150 mcgMain Trial Part: IVX-A12 150 mcg With MF59Main Trial Part: Placebo
RSV: Day 2845.842.90.0
hMPV: Day 2847.952.00.0
PrimaryGeometric 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.

Time frame:
From Day 0 (pre-vaccination) up to Day 28 post-vaccination
Reported as:
Geometric mean · fold rise
Geometric Mean Fold Rise (GMFR) in Serum for RSV-A, RSV-B, hMPV-A, and hMPV-B-Specific NAb Titers
fold riseMain Trial Part: IVX-A12 150 mcgMain Trial Part: IVX-A12 150 mcg With MF59Main Trial Part: Placebo
RSV-A: Day 285.86 (4.59 to 7.48)5.07 (3.92 to 6.57)0.95 (0.85 to 1.06)
RSV-B: Day 283.67 (2.99 to 4.50)3.11 (2.54 to 3.80)1.08 (0.87 to 1.34)
hMPV-A: Day 283.150 (2.544 to 3.900)2.486 (2.022 to 3.058)0.910 (0.764 to 1.083)
hMPV-B: Day 282.426 (2.016 to 2.919)2.746 (2.254 to 3.346)0.936 (0.806 to 1.087)
PrimaryGeometric 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.

Time frame:
From Day 0 (pre-vaccination) up to Day 28 post-vaccination
Reported as:
Geometric mean · fold rise
Geometric Mean Fold Rise (GMFR) in Serum for RSV and hMPV Prefusion F Protein-specific IgG Ab Concentrations
fold riseMain Trial Part: IVX-A12 150 mcgMain Trial Part: IVX-A12 150 mcg With MF59Main Trial Part: Placebo
RSV: Day 283.858 (3.253 to 4.575)3.465 (2.896 to 4.146)0.987 (0.917 to 1.063)
hMPV: Day 284.008 (3.321 to 4.838)4.266 (3.561 to 5.111)0.896 (0.775 to 1.037)
SecondaryNumber 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.

Time frame:
From Day 0 up to the end of study (up to Day 365)
Reported as:
Count of participants · Participants
Number of Participants With Serious Adverse Event (SAE), Medically-attended Adverse Events (MAAEs), and AEs Leading to Trial Withdrawal
ParticipantsMain Trial Part: IVX-A12 150 mcgMain Trial Part: IVX-A12 150 mcg With MF59Main Trial Part: Placebo
SAEs531
MAAEs546021
AE Leading to Study Discontinuation100
SecondaryNumber 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.

Time frame:
From Day 0 up to Day 365 (end of study)
Reported as:
Count of participants · Participants
Number of Participants With Mild, Moderate, or Severe Lower Respiratory Tract Illness (LRTI) Caused by RSV and/or hMPV
ParticipantsMain Trial Part: IVX-A12 150 mcgMain Trial Part: IVX-A12 150 mcg With MF59Main Trial Part: Placebo
Number of Participants With Mild, Moderate, or Severe Lower Respiratory Tract Illness (LRTI) Caused by RSV and/or hMPV420
SecondaryNumber 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.

Time frame:
From Day 0 up to Day 365 (end of study)
Reported as:
Count of participants · Participants
Number of Participants With Mild, Moderate, or Severe LRTI Cases Not Caused by RSV or hMPV
ParticipantsMain Trial Part: IVX-A12 150 mcgMain Trial Part: IVX-A12 150 mcg With MF59Main Trial Part: Placebo
Number of Participants With Mild, Moderate, or Severe LRTI Cases Not Caused by RSV or hMPV14114
SecondaryNumber of Participants With Clinically Significant Safety Laboratory Parameters
Time frame:
At Screening, Days 0, 7 and 28
Reported as:
Number · participants
Number of Participants With Clinically Significant Safety Laboratory Parameters
participantsMain Trial Part: IVX-A12 150 mcgMain Trial Part: IVX-A12 150 mcg With MF59Main Trial Part: Placebo
Number of Participants With Clinically Significant Safety Laboratory Parameters000
SecondaryModel-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.

Time frame:
At Days 180 and 365
Reported as:
Geometric mean · MN50 titer
Model-Adjusted GMTs for RSV-A, RSV-B, hMPV-A, and hMPV-B-specific NAb
MN50 titerMain Trial Part: IVX-A12 150 mcgMain Trial Part: IVX-A12 150 mcg With MF59Main Trial Part: Placebo
RSV-A: Day 1806864.00 (5643.98 to 8347.73)7145.43 (5857.89 to 8715.98)2741.63 (2068.75 to 3633.36)
RSV-A: Day 3654142.06 (3464.80 to 4951.71)3793.79 (3164.62 to 4548.04)1933.12 (1500.23 to 2490.90)
RSV-B: Day 1804536.59 (3856.59 to 5336.50)4152.76 (3516.39 to 4904.29)2205.81 (1744.68 to 2788.83)
RSV-B: Day 3652690.13 (2306.79 to 3137.18)2640.17 (2124.78 to 3085.15)1640.56 (1318.92 to 2040.65)
hMPV-A: Day 180667.67 (582.87 to 764.80)690.94 (601.39 to 793.83)383.31 (315.11 to 466.27)
hMPV-A: Day 365589.68 (508.98 to 683.17)535.25 (460.94 to 621.53)421.28 (341.91 to 519.08)
hMPV-B: Day 1809709.73 (8393.50 to 11232.35)9482.90 (8175.75 to 10999.05)4243.59 (3437.19 to 5239.18)
hMPV-B: Day 3658519.18 (7290.09 to 9955.49)7699.03 (6574.90 to 9015.36)4743.25 (3800.77 to 5919.44)
SecondaryModel-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.

Time frame:
At Days 180, and 365
Reported as:
Geometric mean · ELISA units per milliliter (EU/mL)
Model-Adjusted GMCs for RSV and hMPV Prefusion F Protein-specific IgG Ab Concentrations
ELISA units per milliliter (EU/mL)Main Trial Part: IVX-A12 150 mcgMain Trial Part: IVX-A12 150 mcg With MF59Main Trial Part: Placebo
RSV: Day 180730.14 (640.20 to 832.72)739.32 (646.32 to 845.70)313.74 (259.41 to 379.45)
RSV: Day 365781.54 (704.30 to 867.24)772.83 (695.20 to 859.12)406.42 (350.62 to 471.11)
hMPV: Day 180925.81 (811.73 to 1055.92)937.01 (819.77 to 1071.02)386.81 (319.62 to 468.12)
hMPV: Day 3651018.26 (909.04 to 1140.59)994.03 (886.24 to 1114.94)560.77 (476.93 to 659.35)
SecondaryPercentage 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).

Time frame:
From Day 0 (pre-vaccination) up to Day 180 and Day 365 post-vaccination
Reported as:
Number · percentage of participants
Percentage of Participants With a >=4-fold Increase in Serum RSV-A, RSV-B, hMPV-A, and hMPV-B-specific NAb Titers
percentage of participantsMain Trial Part: IVX-A12 150 mcgMain Trial Part: IVX-A12 150 mcg With MF59Main Trial Part: Placebo
RSV-A: Day 18035.935.96.7
RSV-A: Day 36518.221.62.3
RSV-B: Day 18023.718.74.4
RSV-B: Day 3656.89.12.3
hMPV-A: Day 1807.56.50.0
hMPV-A: Day 3656.84.52.3
hMPV-B: Day 18012.914.10.0
hMPV-B: Day 3659.13.40.0
SecondaryPercentage 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).

Time frame:
From Day 0 (pre-vaccination) up to Days 180, and 365 post-vaccination
Reported as:
Number · percentage of participants
Percentage of Participants With >=4-fold Increase in RSV and hMPV Prefusion F Protein-specific IgG Ab Concentrations
percentage of participantsMain Trial Part: IVX-A12 150 mcgMain Trial Part: IVX-A12 150 mcg With MF59Main Trial Part: Placebo
RSV: Day 18012.912.00.0
RSV: Day 3658.010.20.0
hMPV: Day 18021.519.60.0
hMPV: Day 36527.320.50.0
SecondaryPercentage 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).

Time frame:
From Day 0 (pre-vaccination) up to Days 28, 180, and 365 post-vaccination
Reported as:
Number · percentage of participants
Percentage of Participants With a >=8-fold Increase in Serum RSV-A, RSV-B, hMPV-A, and hMPV-B-specific NAb Titers
percentage of participantsMain Trial Part: IVX-A12 150 mcgMain Trial Part: IVX-A12 150 mcg With MF59Main Trial Part: Placebo
RSV-A: Day 2839.638.80.0
RSV-A: Day 18016.320.72.2
RSV-A: Day 3658.09.10.0
RSV-B: Day 2821.916.32.1
RSV-B: Day 1807.54.40.0
RSV-B: Day 3652.33.40.0
hMPV-A: Day 2813.515.30
hMPV-A: Day 1802.22.20
hMPV-A: Day 3651.100
hMPV-B: Day 2811.519.40
hMPV-B: Day 1804.34.30
hMPV-B: Day 3651.12.30
SecondaryGMFR 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.

Time frame:
From Day 0 (pre-vaccination) up to Day 180 and Day 365 post-vaccination
Reported as:
Geometric mean · fold rise
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
fold riseMain Trial Part: IVX-A12 150 mcgMain Trial Part: IVX-A12 150 mcg With MF59Main Trial Part: Placebo
RSV-A: Day 1803.21 (2.66 to 3.88)3.18 (2.44 to 4.15)1.34 (1.09 to 1.65)
RSV-A: Day 3651.97 (1.63 to 2.39)1.68 (1.33 to 2.13)0.94 (0.78 to 1.13)
RSV-B: Day 1802.02 (1.67 to 2.45)1.88 (1.55 to 2.29)1.02 (0.80 to 1.29)
RSV-B: Day 3651.23 (1.02 to 1.47)1.20 (0.99 to 1.45)0.76 (0.61 to 0.94)
hMPV-A: Day 1801.285 (1.079 to 1.530)1.115 (0.909 to 1.367)0.736 (0.562 to 0.962)
hMPV-A: Day 3651.094 (0.914 to 1.310)0.866 (0.706 to 1.063)0.793 (0.606 to 1.037)
hMPV-B: Day 1801.482 (1.258 to 1.747)1.456 (1.210 to 1.753)0.622 (0.500 to 0.773)
hMPV-B: Day 3651.262 (1.056 to 1.509)1.153 (0.961 to 1.384)0.681 (0.551 to 0.841)
RSV Pre-F: Day 1801.728 (1.487 to 2.007)1.638 (1.380 to 1.945)0.774 (0.665 to 0.901)
RSV Pre-F: Day 3651.844 (1.631 to 2.084)1.687 (1.457 to 1.952)0.973 (0.874 to 1.084)
hMPV Pre-F: Day 1802.157 (1.822 to 2.553)2.118 (1.786 to 2.512)0.794 (0.691 to 0.912)
hMPV Pre-F: Day 3652.380 (2.029 to 2.792)2.293 (1.989 to 2.644)1.149 (0.986 to 1.339)
SecondaryReverse 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.

Time frame:
At Days 28, 180, and 365 post-vaccination
Reported as:
Median · MN50 titer
Reverse Cumulative Distribution (RCD) Curve of Serum NAb Titers and IgG Ab Concentrations
MN50 titerMain Trial Part: IVX-A12 150 mcgMain Trial Part: IVX-A12 150 mcg With MF59Main Trial Part: Placebo
RSV-A: Day 01779.18 (894.07 to 3661.52)2068.22 (984.30 to 4601.80)1764.10 (765.60 to 4136.50)
RSV-A: Day 2812010.69 (4870.35 to 23207.12)10806.21 (4939.50 to 25893.80)1943.00 (772.80 to 3576.80)
RSV-A: Day 1806393.44 (3098.72 to 11645.52)6244.78 (3200.74 to 14601.61)2601.00 (861.10 to 5542.70)
RSV-A: Day 3653793.15 (1869.68 to 6393.49)3630.01 (1828.40 to 8923.32)1769.58 (852.51 to 3427.73)
RSV-B: Day 01965.30 (974.83 to 4937.85)2046.80 (1068.30 to 4611.8)1722.20 (814.40 to 4421.90)
RSV-B: Day 286945.86 (3691.86 to 17581.86)6491.77 (2957.70 to 13097.10)1757.20 (888.60 to 4941.80)
RSV-B: Day 1804226.30 (2123.40 to 10341.40)3427.10 (1924.60 to 7152.40)2192.40 (971.10 to 4308.00)
RSV-B: Day 3652606.69 (1451.24 to 5158.12)2191.31 (1365.43 to 5447.75)1416.93 (641.92 to 2867.91)
hMPV-A: Day 0415.73 (264.05 to 816.11)538.90 (313.30 to 1068.70)360.50 (221.40 to 842.00)
hMPV-A: Day 283.145 (1.479 to 5.837)2.223 (1.303 to 4.294)0.999 (0.643 to 1.306)
hMPV-A: Day 180636.90 (360.30 to 995.40)716.65 (450.90 to 1159.94)320.50 (220.70 to 677.80)
hMPV-A: Day 365518.85 (312.16 to 810.61)514.09 (299.03 to 919.90)313.65 (225.71 to 736.60)
RSV Pre F: Day 0359.94 (222.96 to 694.54)432.69 (257.70 to 802.60)489.60 (184.50 to 662.60)
RSV Pre F: Day 281544.51 (1008.49 to 2328.19)1574.69 (1095.80 to 2313.40)439.00 (191.80 to 675.90)
RSV Pre F: Day 180653.30 (437.50 to 1142.20)774.70 (499.56 to 1176.65)308.60 (133.00 to 628.50)
RSV Pre F: Day 365691.49 (499.49 to 1105.17)879.79 (521.74 to 1355.85)483.45 (210.38 to 730.11)
hMPV Pre F: Day 0410.74 (226.27 to 726.27)524.42 (246.20 to 757.90)531.20 (273.20 to 855.40)
hMPV Pre F: Day 281857.88 (986.18 to 2815.41)1757.83 (1275.90 to 2744.10)444.00 (254.40 to 851.90)
hMPV Pre F: Day 180959.30 (585.40 to 1548.40)920.64 (520.62 to 1585.77)383.20 (251.40 to 672.30)
hMPV Pre F: Day 365967.80 (664.70 to 1543.22)989.21 (684.24 to 1632.10)621.84 (363.65 to 950.72)

Adverse events

Collected over From study start to end of observational extension part (up to Day 509). Non-serious events are listed at a 0% frequency threshold.

Adverse event summary by group
GroupDeathsSeriousOther
Main Trial Part: IVX-A12 150 mcg1/103 (1%)5/103 (4.9%)75/103 (72.8%)
Main Trial Part: IVX-A12 150 mcg With MF590/108 (0%)3/108 (2.8%)81/108 (75%)
Main Trial Part: Placebo0/53 (0%)1/53 (1.9%)42/53 (79.2%)
Observational Extension Part: IVX-A12 150 mcg0/35 (0%)1/35 (2.9%)3/35 (8.6%)
Observational Extension Part: Placebo0/20 (0%)0/20 (0%)1/20 (5%)
Most frequent serious events
Showing 10 of 11
Most frequent serious events
EventMain Trial Part: IVX-A12 150 mcgMain Trial Part: IVX-A12 150 mcg With MF59Main Trial Part: PlaceboObservational Extension Part: IVX-A12 150 mcgObservational Extension Part: Placebo
Deep vein thrombosisVascular disorders2/1030/1080/531/350/20
SeizureNervous system disorders0/1030/1081/530/350/20
Pneumonia viralInfections and infestations1/1030/1080/530/350/20
PyelonephritisInfections and infestations1/1030/1080/530/350/20
Sudden deathGeneral disorders1/1030/1080/530/350/20
Ankle fractureInjury, poisoning and procedural complications1/1030/1080/530/350/20
Stag horn calculusRenal and urinary disorders1/1030/1080/530/350/20
Abscess limbInfections and infestations0/1031/1080/530/350/20
PneumoniaInfections and infestations0/1031/1080/530/350/20
Pneumonia staphylococcalInfections and infestations0/1031/1080/530/350/20
Most frequent other events
Showing 10 of 205
Most frequent other events
EventMain Trial Part: IVX-A12 150 mcgMain Trial Part: IVX-A12 150 mcg With MF59Main Trial Part: PlaceboObservational Extension Part: IVX-A12 150 mcgObservational Extension Part: Placebo
COVID-19Infections and infestations13/10315/1089/530/350/20
CoughRespiratory, thoracic and mediastinal disorders11/10318/1087/530/350/20
Upper respiratory tract infectionInfections and infestations11/10317/1088/530/350/20
HeadacheNervous system disorders8/1039/1088/530/350/20
FatigueGeneral disorders8/10313/1087/530/350/20
RhinorrheaRespiratory, thoracic and mediastinal disorders10/10310/1086/530/350/20
Productive coughRespiratory, thoracic and mediastinal disorders8/1039/1086/530/350/20
Oropharyngeal painRespiratory, thoracic and mediastinal disorders6/1039/1086/530/350/20
Respiratory tract infectionInfections and infestations7/10312/1085/530/350/20
MyalgiaMusculoskeletal and connective tissue disorders10/10311/1084/530/350/20

Baseline characteristics

The Full Analysis Set (FAS) includes all randomized participants who received a dose of IVX-A12 or placebo.

Age, Continuous
Age, Continuous(years)Main Trial Part: IVX-A12 150 mcgMain Trial Part: IVX-A12 150 mcg With MF59Main Trial Part: PlaceboTotal
Mean69.2 ± 6.0569.3 ± 5.8368.8 ± 5.7969.2 ± 5.89
Sex: Female, Male
Sex: Female, Male(Participants)Main Trial Part: IVX-A12 150 mcgMain Trial Part: IVX-A12 150 mcg With MF59Main Trial Part: PlaceboTotal
Female556532152
Male474421112
Ethnicity (NIH/OMB)
Ethnicity (NIH/OMB)(Participants)Main Trial Part: IVX-A12 150 mcgMain Trial Part: IVX-A12 150 mcg With MF59Main Trial Part: PlaceboTotal
Hispanic or Latino1923749
Not Hispanic or Latino828446212
Unknown or Not Reported1203
Race (NIH/OMB)
Race (NIH/OMB)(Participants)Main Trial Part: IVX-A12 150 mcgMain Trial Part: IVX-A12 150 mcg With MF59Main Trial Part: PlaceboTotal
American Indian or Alaska Native0000
Asian0000
Native Hawaiian or Other Pacific Islander0101
Black or African American1214531
White889448230
More than one race0000
Unknown or Not Reported2002
08

Study locations

10 sites
  • AMR Phoenix
    Tempe, Arizona 85281, United States
  • Cenexel RCA
    Hollywood, Florida 33024, United States
  • Clinical Research Atlanta
    Stockbridge, Georgia 30281, United States
  • Velocity Clinical Research-Boise
    Meridian, Idaho 83642, United States
  • ASR, LLC
    Nampa, Idaho 83587, United States
  • Johnson City Clin-Trials (JCCT)
    Lenexa, Kansas 66219, United States
  • AMR Lexington
    Lexington, Kentucky 40509, United States
  • Velocity Clinical Research
    Omaha, Nebraska 68134, United States
  • Rochester Clinical Research, Inc
    Rochester, New York 14609, United States
  • PanAmerican Clinical Research
    Brownsville, Texas 78520, United States
09

References and documents

Study documents

  • Study protocol · Apr 2, 2024
  • Statistical analysis plan · Nov 25, 2024

Documents are hosted by the registry — open the source record to download them.

Individual participant data

Plan to share: No

10

Updates

Tracking since Sep 25, 2026
No changes since tracking began. The registry record was last updated on Dec 5, 2025, before this site started recording changes on Sep 25, 2026. Its history is on ClinicalTrials.gov ↗
11

Registry details

Key details

Study ID
NCT05903183
Lead sponsor
Icosavax, Inc.
Responsible party
Sponsor
First posted
Jun 15, 2023
Start date
May 15, 2023
Primary completion
Jun 5, 2023
Completion
Oct 25, 2024
Results posted
Dec 5, 2025
Last update
Dec 5, 2025

Oversight

Data monitoring committee
Yes
FDA-regulated drug
Yes
FDA-regulated device
No
View the source record on ClinicalTrials.gov ↗

Not currently enrolling

This study is completed, as verified in Nov 2025. You cannot join it, but the record below documents what was studied.

Follow this study

Get an email when the registry record changes — status, dates, results — or when someone posts here.

Sign in to follow

Discussion

Questions and observations about this study, from anyone following it. Not medical advice, and not a channel to the study team — their contact details are on the registry record.

Sign in to join the discussion. Reading takes no account; posting does. You choose a display name, and a pseudonym is the default.

Nothing here yet. If you are running this trial, taking part in it, or weighing whether to, this is the place to say so.

Other studies from this sponsor

Icosavax, Inc.

Start the discussion