CompletedNCT06106581Updated Aug 13, 2026Results posted

A Phase 2 Clinical Trial of VLA1553 in Healthy Children Aged 1 to 11 Years

A Phase 2 interventional study of VLA1553 full dose and VLA1553 half dose in Chikungunya Virus Infection, sponsored by Valneva Austria GmbH. Completed at 3 sites in 2 countries. Open to participants aged 1 Year to 11 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-08-13.

Sponsored by Valneva Austria GmbH (part of Valneva) · Phase 2, Interventional, and Prevention

Phase: Phase 2
Study type: Interventional
Enrollment: 304
Allocation: Randomized
Ages: 1 Year to 11 Years
Sex: All

Study summary

This is a multicenter, prospective, randomized, observer-blinded, three arm, phase 2 clinical trial evaluating the full dose formulation of VLA1553, half dose formulation of VLA1553 and control.

At least 300 male and female healthy children aged 1 to 11 years will be enrolled and the overall distribution of participants will be 2:2:1 to the two VLA1553 dose groups (n=120 each) or control (n=60).

Read the detailed description

This is a multicenter, prospective, randomized, observer-blinded, three arm, phase 2 clinical trial evaluating the full dose formulation of VLA1553, half dose formulation of VLA1553 and control (Nimenrix, a tetravalent meningococcal vaccine - Men ACWY).

As a safety precaution measure, the first 30 sentinel participants will be enrolled into the trial in an open-label fashion according to an age step down scheme.

After sentinel analysis, participants will be enrolled in a blinded, randomized manner into three Trial Arms. Within each treatment arm participants will be stratified into three age strata:

Stratum A: 7 to 11 years -children from their 7th birthday until the day before their 12th birthday.

Stratum B: 3 to 6 years - children from their 3rd birthday until the day before their 7th birthday.

Stratum C: 1 to 2 years - children from their 1st birthday until the day before their 3rd birthday.

Age strata for the VLA1553 treatment arms are targeted to be equal in size, i.e., approximately 40 per age stratum.

Conditions studied

Chikungunya Virus Infection

Browse trials for

Chikungunya Fever 88

In context

Chikungunya Fever

88 studies on the registry are indexed under Chikungunya Fever; 21 are open to participants now.

This study's enrollment of 304 is above the median of 263 across 57 interventional studies indexed under Chikungunya Fever.

Browse Chikungunya Fever studies →

Lead sponsor

Valneva Austria GmbH is the lead sponsor of 44 studies on the registry; 2 are open to participants now.

Of its 7 completed or terminated interventional studies of FDA-regulated products, 4 (57%) have results posted.

First submitted after Valneva Austria GmbH became part of Valneva.

Browse Valneva Austria GmbH studies →All Valneva studies →

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

Who can participate

Ages eligible: 1 Year to 11 Years
Sexes eligible: All
Accepts healthy volunteers: Yes

Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.

Inclusion criteria

Male or female healthy children aged 7 to 11 years for Stratum A, 3 to 6 years for Stratum B and 1 to 2 years for Stratum C at the time of vaccination;
Written by the participant's parent(s)/Legally Acceptable Representative(s) ((LAR(s)), according to local requirements, and written informed assent of the participant, if applicable;
Participant was seropositive for previous CHIKV exposure (i.e., IgM+/IgG+ or IgM-/IgG+) or seronegative (i.e., IgM-/IgG-); or participants with any borderline IgM or IgG element (IgM borderline/IgG-, IgM-/IgG borderline, or IgM borderline/IgG borderline were mapped to seronegative group; participants with enzyme-linked immunosorbent assay (ELISA) result IgM borderline/IgG+ were mapped to seropositive group);

Exclusion criteria

Exclusion Criteria:

Participant was IgM+/IgG- does not qualify for participation in this trial.
Participant was taking medication or other treatment for unresolved symptoms attributed to a previous CHIKV infection; or had participated in a clinical trial involving an CHIKV vaccine;
Participant had an acute or recent infection (and was not symptom-free in the week prior to the Screening Visit (Visit 0))
Participant had received another within 28 days or inactivated vaccine (includes messenger ribonucleic acid [mRNA] vaccines) within 14 days prior to vaccination in this trial or planned to receive a live virus vaccine within 28 days or inactivated vaccine within 14 days after vaccination;
Participant had abnormal findings in any required trial investigations (including medical history, physical examination, and clinical laboratory) considered by the Investigator which posed a risk for participation in the trial based on his/her judgment;
Participant had an ongoing medical history of or currently had acute or progressive, unstable or uncontrolled clinical conditions (e.g., cardiovascular, respiratory, neurologic, psychiatric, or rheumatologic conditions) that posed a risk for participation in the trial, based on Investigator's clinical judgment. Examples included individuals with poorly controlled or unstable disease, ongoing suspected or active inflammation, or poor compliance with pharmacologic treatment, or presence of high-risk comorbidities (e.g., significant cardiopulmonary disease);
Participant had a history of immune-mediated or clinically relevant arthritis/arthralgia;
Participant had a known or suspected defect of the immune system that could be expected to influence the immune response to the vaccine, such as Participants with congenital or acquired immunodeficiency, including infection with , status post organ transplantation or immuno- suppressive therapy within 4 weeks prior to Visit 1. therapy was defined as administration of chronic (longer than 14 days) prednisone or equivalent ≥0.05 mg/kg/day within 4 weeks prior to trial entry, radiation therapy or immunosuppressive cytotoxic drugs/ monoclonal antibodies in the previous 3 years; topical and inhaled were allowed.
Participant had a history of any vaccine-related contraindicating event (e.g., anaphylaxis, allergy to components of the vaccine or the control vaccine, other known including febrile convulsions);
Participant presented with clinical conditions representing severe bleeding disorders and medications interfering with blood clotting;
Participant received blood-derived products (e.g. plasma) within 180 days prior to vaccination in this trial;
Participant had participated in another clinical trial involving an investigational medicinal product (IMP) or device within 30 days prior to vaccination or was scheduled to participate in another clinical trial involving an IMP, or device during the course of this trial;
Participant had any condition that, in the opinion of the Investigator, could compromise the participant's well-being, might interfere with evaluation of trial endpoints, or would limit the participant's ability to complete the trial;
Participant/ Participant's parent(s)/LAR(s) was/were a member of the team conducting the trial or in a dependent relationship with one of the trial team members. Dependent relationships included close relatives (i.e., children, partner/spouse, siblings, parent(s)/LAR[s]) as well as employees of the Investigator or site personnel conducting the trial.

Terms in these criteria, in plain language(8)

Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.

Informed consent

Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.

You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.

Investigational drug or device

A drug or device being studied in a clinical trial.

It may be new, or already approved and being studied for another use, dose or form. Criteria often leave out people who took part in another study of one within a recent period, commonly 30 days or five half-lives.

Live vaccines

Vaccines made with a weakened form of the germ, such as measles–mumps–rubella (MMR), chickenpox and yellow fever. They can be risky when the immune system is weakened. Flu injections are not live; the nasal flu spray is.

Clinically significant

Judged by the study doctor to matter for your health or for the study. It is a doctor’s decision, so ask the study team if you are unsure whether something counts.

HIV

The human immunodeficiency virus, which weakens the immune system.

Many studies now accept people whose HIV is controlled on treatment, judged by the viral load and the CD4 count. Check the limits this study sets.

Immunosuppression

A weakened immune system. It can come from an illness, such as HIV or some blood cancers, or from medicines that turn the immune system down, for example after an organ transplant or for an autoimmune disease; steroids at higher doses count.

Read whether the line is about a condition or about medicines, and which medicines and doses it means.

Corticosteroids (steroids)

Anti-inflammatory medicines such as prednisone, prednisolone and dexamethasone — not the anabolic steroids used for muscle.

Studies differ in what they allow: check which steroid medicines, routes (tablets, injections, creams, inhalers, eye drops) and doses this study accepts.

Contraindication

A reason a treatment, test or procedure should not be given to a particular person, such as an allergy, another illness or a medicine they take.

Study design

Phase: Phase 2
Primary purpose: Prevention
Allocation: Randomized
Intervention model: Parallel assignment
Masking: Quadruple (Participant, Care provider, Investigator, Outcomes assessor)
Enrollment: 304 participants (actual)

Study arms

Experimental
VLA1553 full dose
Biological: VLA1553 full dose
Experimental
VLA1553 half dose
Biological: VLA1553 half dose
Active comparator
Control
Single intramuscular vaccination on Day 1 with Nimenrix (Men ACWY vaccine), a conjugate vaccine indicated for the active immunization
Biological: Control

Interventions

BiologicalVLA1553 full dose
Single intramuscular vaccination on Day 1 with VLA1553 full dose, a lyophilized live-attenuated Chikungunya vaccine candidate
BiologicalVLA1553 half dose
Single intramuscular vaccination on Day 1 with VLA1553 half dose, a lyophilized live-attenuated Chikungunya vaccine candidate
BiologicalControl
Nimenrix

What researchers measure

Primary outcomes

Number of Participants With Solicited Injection Site Reactions
Frequency and severity of solicited injection site and solicited systemic reactions within 14 days post-vaccination.
Time frame: within 14 days post-vaccination
Severity of Solicited Injection Site Reactions
Time frame: within 14 days post-vaccination
Number of Participants With Solicited Systemic Reactions
Time frame: within 14 days post-vaccination
Severity of Solicited Systemic Reactions
Time frame: within 14 days post-vaccination

Secondary outcomes

Number of Participants With Any Adverse Event (AE)
Time frame: within 28 days post-vaccination
Severity of Any Adverse Event (AE)
In the Outcome measure "Severity of any AE", subjects may be represented in more than one AE category. Therefore, the total number of subjects with any AE may be lower than the sum of the numbers of subjects in the individual AE categories (solicited / unsolicited AE).
Time frame: within 28 days post-vaccination
Number of Participants With of Unsolicited AE
Time frame: until Month 6 (Day 180) and Month 12 (Day 365) post-vaccination
Severity of Unsolicited AE
Time frame: until Month 6 (Day 180) and Month 12 (Day 365) post-vaccination
Number of Participants With Any Serious Adverse Event (SAE)
Time frame: until Month 6 (Day 180) and Month 12 (Day 365) post-vaccination
Number of Participants With Any Early Onset Adverse Event of Special Interest (AESI)
Early onset AESI were defined as: 1. Fever (≥ 38.0 °c / 100.4 °f,) AND 2. symptoms suggesting acute (poly)arthralgia/arthritis, myalgia, neurological symptoms (e.g., for meningoencephalitis, acute encephalitis, headache, seizures), back pain, lymphadenopathy, cardiac or ocular symptoms (e.g., for uveitis and retinitis); OR one or more of the following signs and symptoms: macular to maculopapular rash (sometimes with cutaneous pruritus \[foot plant\]), pigmentary changes, bullous rash/ skin blistering, purpura, ecchymosis and 3. Onset of symptoms 2 to 21 days after vaccination AND 4. Duration of event ≥ 3 days.
Time frame: 2 to 21 days post-vaccination
Severity of Any Early Onset Adverse Event of Special Interest (AESI)
Time frame: 2 to 21 days post-vaccination
Number of Participants With Any Late Onset Adverse Event of Special Interest (AESI)
Time frame: Starting 22 days post-vaccination until end of trial, 12 months post-vaccination
Severity of Any Late Onset Adverse Event of Special Interest (AESI)
Time frame: Starting 22 days post-vaccination until end of trial, 12 months post-vaccination
Assessment of Viremia on Days 1, 4, 8 and 15
Number of participants with viremic results, including quantifiable results and results below LLOQ, by visit and by pooled trial arm. Day 29 was only tested, if Day 15 was tested positive. Viremia is measured in genome copy equivalents per milliliter (GCE/mL). All quantifiable results and results below LLOQ (\< 3214.4 GCE/mL), but above the LOD, are considered "viremic". A result of "not detected" or below LOD (\<1071,4 GCE/mL) is included as "non-viremic".
Time frame: on Days 1, 4, 8 and 15 and beyond as applicable
Immune Response in Baseline Seronegative Participants as Measured by CHIKV-specific Neutralizing Antibody Titers
Immune Response provided by Geometric Mean Titers (GMTs) in Baseline Seronegative Participants pooled by Trial Arm up to 12 months post vaccination.
Time frame: on Day 1, Day 15, Day 29, Day 85, Day 180 and Month 12 post-vaccination
Immune Response as Measured by CHIKV-specific Neutralizing Antibody Titers by Age Group and Trial Arm.
Immune Response provided by Geometric Mean Titers (GMTs) by Visit, by Age Group and Trial Arm up to 12 months post vaccination.
Time frame: on Day 1, Day 15, Day 29, Day 85, Day 180 and Month 12 post-vaccination
Immune Response Measured by CHIKV-specific Neutralizing Antibody Titers Pooled by Dose
Immune Response provided by Geometric Mean Titers (GMTs) by Visit, pooled by Trial Arm up to 12 months post vaccination.
Time frame: on Day 1, Day 15, Day 29, Day 85, Day 180 and Month 12 post-vaccination
Percentage of Participants Seronegative at Baseline With Seroconversion as Compared to Baseline
Percentage of participants seronegative at baseline with Seroconversion (defined as \>4-fold titer change compared to baseline) by Visit Pooled by Trial Arm
Time frame: at Day 15, Day 29, Day 85, Day 180 and Month 12
Percentage of Participants Seropositive at Baseline With Seroconversion as Compared to Baseline
Percentage of participants seropositive at baseline with Seroconversion (defined as \>4-fold titer change compared to baseline) by Visit Pooled by Trial Arm.
Time frame: at Day 15, Day 29, Day 85, Day 180 and Month 12
Percentage of Participants With Seroconversion as Compared to Baseline Stratified by Age Stratum
Percentage of participants with Seroconversion (defined as \>4-fold titer change compared to baseline) by Visit by Age Group and Trial Arm.
Time frame: at Day 15, Day 29, Day 85, Day 180 and Month 12
Percentage of Participants With Seroconversion as Compared to Baseline by Dose
Percentage of participants with Seroconversion (defined as \>4-fold titer change compared to baseline) by Visit Pooled by Trial Arm
Time frame: at Day 15, Day 29, Day 85, Day 180 and Month 12
Percentage of Participants Seronegative at Baseline With a Seroresponse (Defined as PRNT50 ≥150 for Baseline Negative Participants) by Dose
Percentage of Participants with Seroresponse for CHIKV-Specific Neutralizing Antibody Titers (defined as PRNT50 ≥150) by Visit Pooled by Trial Arm.
Time frame: on Day 15, Day 29, Day 85, Day 180 and Month 12 post-vaccination
Percentage of Participants With a Seroresponse Stratified by Age Stratum
Percentage of Participants with Seroresponse for CHIKV-Specific Neutralizing Antibody Titers (defined as PRNT50 ≥150) by Visit by Age Group and Trial Arm.
Time frame: on Day 15, Day 29, Day 85, Day 180 and Month 12 post-vaccination
Percentage of Participants With a Seroresponse Stratified by Dose
Percentage of Participants with Seroresponse for CHIKV-Specific Neutralizing Antibody Titers (defined as PRNT50 ≥150) by Visit Pooled by Trial Arm.
Time frame: on Day 15, Day 29, Day 85, Day 180 and Month 12 post-vaccination
Fold Change of CHIKV-specific Neutralizing Antibody Titers as Compared to Baseline in Participants Seronegative at Baseline
Fold Change for CHIKV-Specific Neutralizing Antibody Titers in seronegative Participants by Visit Pooled by Trial Arm.
Time frame: at Days 15, 29, 85, 180 and at Month 12 post-vaccination
Fold Change of CHIKV-specific Neutralizing Antibody Titers as Compared to Baseline in Seropositive Participants
Fold Change for CHIKV-Specific Neutralizing Antibody Titers in seropositive Participants by Visit Pooled by Trial Arm.
Time frame: at Days 15, 29, 85, 180 and at Month 12 post-vaccination
Fold Change of CHIKV-specific Neutralizing Antibody Titers as Compared to Baseline Stratified by Age Stratum
Fold Change for CHIKV-Specific Neutralizing Antibody Titers by Visit by Age Group and Trial Arm.
Time frame: at Days 15, 29, 85, 180 and at Month 12 post-vaccination
Fold Change of CHIKV-specific Neutralizing Antibody Titers as Compared to Baseline Stratified by Dose
Fold Change for CHIKV-Specific Neutralizing Antibody Titers by Visit Pooled by Trial Arm.
Time frame: at Days 15, 29, 85, 180 and at Month 12 post-vaccination
Percentage of Participants Seronegative at Baseline Reaching an at Least 4-fold, 8-fold, 16-fold or 64-fold Change in CHIKV-specific Neutralizing Antibody Titers Compared to Baseline
Percentage of Participants Reaching a 4-/8-/16-/64-Fold Change in Titers by Visit Pooled by Trial Arm.
Time frame: at Day 15, Day 29, Day 85, Day 180 and Month 12
Percentage of Participants Reaching an at Least 4-fold, 8-fold, 16-fold or 64-fold Change in CHIKV-specific Neutralizing Antibody Titers Compared to Baseline Stratified by Age Stratum
Percentage of Participants Reaching a 4-/8-/16-/64-Fold Change in Titers by Visit by Age Group and Trial Arm.
Time frame: at Day 15, Day 29, Day 85, Day 180 and Month 12
Percentage of Participants Reaching an at Least 4-fold, 8-fold, 16-fold or 64-fold Change in CHIKV-specific Neutralizing Antibody Titers Compared to Baseline by Dose
Percentage of Participants Reaching a 4-/8-/16-/64-Fold Change in Titers by Visit Pooled by Trial Arm.
Time frame: at Day 15, Day 29, Day 85, Day 180 and Month 12

Results

Posted Aug 13, 2026

Participant flow

Participant flow — Overall Study
Milestone	VLA1553 Half Dose	VLA1553 Full Dose	Control
Started	119	124	61
Completed	115	122	60
Not completed	4	2	1
Withdrew: Withdrawal by subject	1	0	1
Withdrew: Lost to follow-up	2	1	0
Withdrew: Physician decision	1	0	0
Withdrew: Participant was out of town and was not back within the time window	0	1	0

Outcome measures

PrimaryNumber of Participants With Solicited Injection Site Reactions

Frequency and severity of solicited injection site and solicited systemic reactions within 14 days post-vaccination.

Time frame:: within 14 days post-vaccination
Reported as:: Count of participants · Participants

Number of Participants With Solicited Injection Site Reactions
Participants	VLA1553 Half Dose - 7-11 Years	VLA1553 Full Dose - 7-11 Years	Control - 7-11 Years	VLA1553 Half Dose - 3-6 Years	VLA1553 Full Dose - 3-6 Years	Control - 3-6 Years	VLA1553 Half Dose - 1-2 Years	VLA1553 Full Dose - 1-2 Years	Control - 1-2 Years
Number of Participants With Solicited Injection Site Reactions	12	8	7	6	7	0	3	1	1

PrimarySeverity of Solicited Injection Site Reactions

Time frame:: within 14 days post-vaccination
Reported as:: Count of participants · Participants

Severity of Solicited Injection Site Reactions
Participants	VLA1553 Half Dose - 7-11 Years	VLA1553 Full Dose - 7-11 Years	Control - 7-11 Years	VLA1553 Half Dose - 3-6 Years	VLA1553 Full Dose - 3-6 Years	VLA1553 Half Dose - 1-2 Years	VLA1553 Full Dose - 1-2 Years	Control - 1-2 Years
Grade 4	0	0	0	0	0	0	0	0
Grade 3	0	0	0	0	0	0	0	0
Grade 2	5	1	2	0	0	0	0	0
Grade 1	9	7	6	6	7	3	1	1

PrimaryNumber of Participants With Solicited Systemic Reactions

Time frame:: within 14 days post-vaccination
Reported as:: Count of participants · Participants

Number of Participants With Solicited Systemic Reactions
Participants	VLA1553 Half Dose - 7-11 Years	VLA1553 Full Dose - 7-11 Years	Control - 7-11 Years	VLA1553 Half Dose - 3-6 Years	VLA1553 Full Dose - 3-6 Years	Control - 3-6 Years	VLA1553 Half Dose - 1-2 Years	VLA1553 Full Dose - 1-2 Years	Control - 1-2 Years
Number of Participants With Solicited Systemic Reactions	11	17	3	10	10	4	9	15	3

PrimarySeverity of Solicited Systemic Reactions

Time frame:: within 14 days post-vaccination
Reported as:: Count of participants · Participants

Severity of Solicited Systemic Reactions
Participants	VLA1553 Half Dose - 7-11 Years	VLA1553 Full Dose - 7-11 Years	Control - 7-11 Years	VLA1553 Half Dose - 3-6 Years	VLA1553 Full Dose - 3-6 Years	Control - 3-6 Years	VLA1553 Half Dose - 1-2 Years	VLA1553 Full Dose - 1-2 Years	Control - 1-2 Years
Grade 4	0	0	0	0	0	0	1	0	0
Grade 3	0	0	0	0	3	0	1	1	0
Grade 2	8	3	0	0	2	3	1	3	1
Grade 1	6	15	3	10	9	1	7	13	2

SecondaryNumber of Participants With Any Adverse Event (AE)

Time frame:: within 28 days post-vaccination
Reported as:: Count of participants · Participants

Number of Participants With Any Adverse Event (AE)
Participants	VLA1553 Half Dose - 7-11 Years	VLA1553 Full Dose - 7-11 Years	Control - 7-11 Years	VLA1553 Half Dose - 3-6 Years	VLA1553 Full Dose - 3-6 Years	Control - 3-6 Years	VLA1553 Half Dose - 1-2 Years	VLA1553 Full Dose - 1-2 Years	Control - 1-2 Years
Number of Participants With Any Adverse Event (AE)	22	23	11	20	16	6	16	20	8

SecondarySeverity of Any Adverse Event (AE)

In the Outcome measure "Severity of any AE", subjects may be represented in more than one AE category. Therefore, the total number of subjects with any AE may be lower than the sum of the numbers of subjects in the individual AE categories (solicited / unsolicited AE).

Time frame:: within 28 days post-vaccination
Reported as:: Count of participants · Participants

Severity of Any Adverse Event (AE)
Participants	VLA1553 Half Dose - 7-11 Years	VLA1553 Full Dose - 7-11 Years	Control - 7-11 Years	VLA1553 Half Dose - 3-6 Years	VLA1553 Full Dose - 3-6 Years	Control - 3-6 Years	VLA1553 Half Dose - 1-2 Years	VLA1553 Full Dose - 1-2 Years	Control - 1-2 Years
any solicited AE	17	20	9	14	12	4	10	15	3
solicited AE - Grade 4	0	0	0	0	0	0	1	0	0
solicited AE - Grade 3	0	0	0	0	3	0	1	1	0
solicited AE - Grade 2	11	4	2	0	2	3	1	3	1
solicited AE - Grade 1	6	16	7	14	7	1	7	11	2
any unsolicited AE	10	13	6	12	11	5	12	13	6
unsolicited AE - Grade 4	0	0	0	0	0	0	0	0	0
unsolicited AE - Grade 3	1	0	0	0	0	0	1	0	0
unsolicited AE - Grade 2	2	0	1	1	2	0	0	0	0
unsolicited AE - Grade 1	7	13	5	11	9	5	11	13	6

SecondaryNumber of Participants With of Unsolicited AE

Time frame:: until Month 6 (Day 180) and Month 12 (Day 365) post-vaccination
Reported as:: Count of participants · Participants

Number of Participants With of Unsolicited AE
Participants	VLA1553 Half Dose - 7-11 Years	VLA1553 Full Dose - 7-11 Years	Control - 7-11 Years	VLA1553 Half Dose - 3-6 Years	VLA1553 Full Dose - 3-6 Years	Control - 3-6 Years	VLA1553 Half Dose - 1-2 Years	VLA1553 Full Dose - 1-2 Years	Control - 1-2 Years
Month 6 - Day 180	25	25	11	27	20	13	27	28	14
Month 12 - Day 365	25	31	12	30	24	16	29	33	17

SecondarySeverity of Unsolicited AE

Time frame:: until Month 6 (Day 180) and Month 12 (Day 365) post-vaccination
Reported as:: Count of participants · Participants

Severity of Unsolicited AE
Participants	VLA1553 Half Dose - 7-11 Years	VLA1553 Full Dose - 7-11 Years	Control - 7-11 Years	VLA1553 Half Dose - 3-6 Years	VLA1553 Full Dose - 3-6 Years	Control - 3-6 Years	VLA1553 Half Dose - 1-2 Years	VLA1553 Full Dose - 1-2 Years	Control - 1-2 Years
Month 6 - Grade 4	0	0	0	0	0	0	0	0	0
Month 6 - Grade 3	1	2	0	1	0	0	3	2	0
Month 6 - Grade 2	8	4	3	8	4	2	8	7	4
Month 6 - Grade 1	16	19	8	18	16	11	16	19	10
Month 12 - Grade 4	0	0	0	0	0	0	0	0	1
Month 12 - Grade 3	1	4	1	2	0	0	3	2	0
Month 12 - Grade 2	10	5	4	9	8	5	11	16	6
Month 12 - Grade 1	14	22	7	19	16	11	15	15	10

SecondaryNumber of Participants With Any Serious Adverse Event (SAE)

Time frame:: until Month 6 (Day 180) and Month 12 (Day 365) post-vaccination
Reported as:: Count of participants · Participants

Number of Participants With Any Serious Adverse Event (SAE)
Participants	VLA1553 Half Dose - 7-11 Years	VLA1553 Full Dose - 7-11 Years	Control - 7-11 Years	VLA1553 Half Dose - 3-6 Years	VLA1553 Full Dose - 3-6 Years	Control - 3-6 Years	VLA1553 Half Dose - 1-2 Years	VLA1553 Full Dose - 1-2 Years	Control - 1-2 Years
Month 6 - Day 180	1	0	0	0	0	0	0	1	0
Month 12 - ay 365	1	2	0	1	0	0	0	2	1

SecondaryNumber of Participants With Any Early Onset Adverse Event of Special Interest (AESI)

Early onset AESI were defined as: 1. Fever (≥ 38.0 °c / 100.4 °f,) AND 2. symptoms suggesting acute (poly)arthralgia/arthritis, myalgia, neurological symptoms (e.g., for meningoencephalitis, acute encephalitis, headache, seizures), back pain, lymphadenopathy, cardiac or ocular symptoms (e.g., for uveitis and retinitis); OR one or more of the following signs and symptoms: macular to maculopapular rash (sometimes with cutaneous pruritus \[foot plant\]), pigmentary changes, bullous rash/ skin blistering, purpura, ecchymosis and 3. Onset of symptoms 2 to 21 days after vaccination AND 4. Duration of event ≥ 3 days.

Time frame:: 2 to 21 days post-vaccination
Reported as:: Count of participants · Participants

Number of Participants With Any Early Onset Adverse Event of Special Interest (AESI)
Participants	VLA1553 Half Dose	VLA1553 Full Dose	Control
Number of Participants With Any Early Onset Adverse Event of Special Interest (AESI)	3	0	0

SecondarySeverity of Any Early Onset Adverse Event of Special Interest (AESI)

Time frame:: 2 to 21 days post-vaccination
Reported as:: Count of participants · Participants

Severity of Any Early Onset Adverse Event of Special Interest (AESI)
Participants	VLA1553 Half Dose	VLA1553 Full Dose	Control
Grade 4	0	0	0
Grade 3	0	0	0
Grade 2	2	0	0
Grade 1	1	0	0

SecondaryNumber of Participants With Any Late Onset Adverse Event of Special Interest (AESI)

Time frame:: Starting 22 days post-vaccination until end of trial, 12 months post-vaccination
Reported as:: Count of participants · Participants

Number of Participants With Any Late Onset Adverse Event of Special Interest (AESI)
Participants	VLA1553 Half Dose	VLA1553 Full Dose	Control
Number of Participants With Any Late Onset Adverse Event of Special Interest (AESI)	2	0	0

SecondarySeverity of Any Late Onset Adverse Event of Special Interest (AESI)

Time frame:: Starting 22 days post-vaccination until end of trial, 12 months post-vaccination
Reported as:: Count of participants · Participants

Severity of Any Late Onset Adverse Event of Special Interest (AESI)
Participants	VLA1553 Half Dose	VLA1553 Full Dose	Control
Grade 4	0	0	0
Grade 3	0	0	0
Grade 2	1	0	0
Grade 1	1	0	0

SecondaryAssessment of Viremia on Days 1, 4, 8 and 15

Number of participants with viremic results, including quantifiable results and results below LLOQ, by visit and by pooled trial arm. Day 29 was only tested, if Day 15 was tested positive. Viremia is measured in genome copy equivalents per milliliter (GCE/mL). All quantifiable results and results below LLOQ (\< 3214.4 GCE/mL), but above the LOD, are considered "viremic". A result of "not detected" or below LOD (\<1071,4 GCE/mL) is included as "non-viremic".

Time frame:: on Days 1, 4, 8 and 15 and beyond as applicable
Reported as:: Count of participants · Participants

Assessment of Viremia on Days 1, 4, 8 and 15
Participants	VLA1553 Half Dose	VLA1553 Full Dose
Visit 1 - Day 1 : Quantifiable	0	0
Visit 1 - Day 1 : Below LLOQ	0	0
Visit 2 - Day 4 : Quantifiable	12	23
Visit 2 - Day 4 : Below LLOQ	6	10
Visit 3 - Day 8 : Quantifiable	10	8
Visit 3 - Day 8 : Below LLOQ	6	5
Visit 4 - Day 15 : Quantifiable	1	0
Visit 4 - Day 15 : Below LLOQ	0	0
Visit 5 - Day 29 : Quantifiable	0	0
Visit 5 - Day 29 : Below LLOQ	0	0

SecondaryImmune Response in Baseline Seronegative Participants as Measured by CHIKV-specific Neutralizing Antibody Titers

Immune Response provided by Geometric Mean Titers (GMTs) in Baseline Seronegative Participants pooled by Trial Arm up to 12 months post vaccination.

Time frame:: on Day 1, Day 15, Day 29, Day 85, Day 180 and Month 12 post-vaccination
Reported as:: Geometric mean · titer

Immune Response in Baseline Seronegative Participants as Measured by CHIKV-specific Neutralizing Antibody Titers
titer	VLA1553 Half Dose	VLA1553 Full Dose	Control
Visit 1 - Day 1	10.1 (9.9 to 10.3)	10.0 (10.0 to 10.0)	10.3 (9.9 to 10.7)
Visit 4 - Day 15	1046.1 (726.6 to 1506.0)	1949.9 (1513.7 to 2511.8)	10.2 (9.8 to 10.7)
Visit 5 - Day 29	1845.4 (1300.3 to 2618.8)	2860.6 (2267.8 to 3608.3)	10.3 (9.9 to 10.8)
Visit 6 - Day 85	630.8 (465.8 to 854.4)	1031.5 (830.6 to 1281.0)	10.0 (10.0 to 10.0)
Visit 7 - Day 180	514.2 (383.2 to 690.0)	813.7 (658.5 to 1005.4)	10.0 (10.0 to 10.0)
Visit 8 - Day 365	798.7 (573.4 to 1112.5)	1355.7 (1071.5 to 1715.2)	10.5 (9.9 to 11.0)

SecondaryImmune Response as Measured by CHIKV-specific Neutralizing Antibody Titers by Age Group and Trial Arm.

Immune Response provided by Geometric Mean Titers (GMTs) by Visit, by Age Group and Trial Arm up to 12 months post vaccination.

Time frame:: on Day 1, Day 15, Day 29, Day 85, Day 180 and Month 12 post-vaccination
Reported as:: Geometric mean · titer

Immune Response as Measured by CHIKV-specific Neutralizing Antibody Titers by Age Group and Trial Arm.
titer	VLA1553 Half Dose - 7-11 Years	VLA1553 Full Dose - 7-11 Years	Control - 7-11 Years	VLA1553 Half Dose - 3-6 Years	VLA1553 Full Dose - 3-6 Years	Control - 3-6 Years	VLA1553 Half Dose - 1-2 Years	VLA1553 Full Dose - 1-2 Years	Control - 1-2 Years
Visit 1 - Day 1	10.0 (10.0 to 10.0)	10.0 (10.0 to 10.0)	10.7 (9.3 to 12.3)	10.3 (9.7 to 10.8)	10.0 (10.0 to 10.0)	10.0 (10.0 to 10.0)	10.0 (10.0 to 10.0)	10.0 (10.0 to 10.0)	10.4 (9.6 to 11.1)
Visit 4 - Day 15	836.0 (443.2 to 1576.7)	2214.5 (1716.3 to 2857.2)	10.0 (10.0 to 10.0)	1437.4 (836.1 to 2471.1)	2275.4 (1518.3 to 3410.3)	10.0 (10.0 to 10.0)	960.3 (462.7 to 1993.1)	1474.5 (808.7 to 2688.8)	10.7 (9.3 to 12.3)
Visit 5 - Day 29	1979.1 (941.9 to 4158.4)	3443.6 (2957.0 to 4010.3)	10.0 (10.0 to 10.0)	2170.2 (1304.9 to 3609.2)	3134.8 (2108.4 to 4660.7)	10.0 (10.0 to 10.0)	1439.2 (730.0 to 2837.1)	2161.7 (1235.0 to 3783.7)	11.0 (9.6 to 12.5)
Visit 6 - Day 85	634.5 (347.7 to 1157.7)	1240.8 (1003.9 to 1533.6)	10.0 (10.0 to 10.0)	763.4 (497.7 to 1170.9)	1073.7 (763.8 to 1509.2)	10.0 (10.0 to 10.0)	517.5 (277.9 to 963.8)	831.1 (500.1 to 1381.1)	10.0 (10.0 to 10.0)
Visit 7 - Day 180	573.8 (315.9 to 1042.1)	835.4 (648.3 to 1076.7)	10.0 (10.0 to 10.0)	468.0 (313.2 to 699.4)	872.4 (635.4 to 1197.8)	10.0 (10.0 to 10.0)	506.0 (272.4 to 940.0)	820.1 (517.8 to 1298.9)	10.0 (10.0 to 10.0)
Visit 8 - Day 365	693.3 (376.4 to 1277.2)	1451.0 (1102.4 to 1909.9)	10.7 (9.3 to 12.3)	858.6 (524.5 to 1405.4)	1382.2 (975.0 to 1959.5)	10.0 (10.0 to 10.0)	814.0 (400.4 to 1654.7)	1242.6 (703.3 to 2195.8)	10.8 (9.6 to 12.2)

SecondaryImmune Response Measured by CHIKV-specific Neutralizing Antibody Titers Pooled by Dose

Immune Response provided by Geometric Mean Titers (GMTs) by Visit, pooled by Trial Arm up to 12 months post vaccination.

Time frame:: on Day 1, Day 15, Day 29, Day 85, Day 180 and Month 12 post-vaccination
Reported as:: Geometric mean · titer

Immune Response Measured by CHIKV-specific Neutralizing Antibody Titers Pooled by Dose
titer	VLA1553 Half Dose	VLA1553 Full Dose	Control
Visit 1 - Day 1	10.1 (9.9 to 10.3)	10.0 (10.0 to 10.0)	10.3 (9.9 to 10.7)
Visit 4 - Day 15	1073.6 (748.1 to 1540.7)	1944.8 (1506.5 to 2510.8)	10.2 (9.8 to 10.8)
Visit 5 - Day 29	1829.3 (1280.8 to 2612.8)	2843.6 (2247.1 to 3598.5)	10.3 (9.9 to 10.8)
Visit 6 - Day 85	631.4 (463.5 to 860.2)	1025.9 (824.8 to 1276.2)	10.0 (10.0 to 10.0)
Visit 7 - Day 180	508.5 (377.1 to 685.8)	842.5 (689.1 to 1030.1)	10.0 (10.0 to 10.0)
Visit 8 - Day 365	794.5 (566.8 to 1113.7)	1353.4 (1067.5 to 1715.8)	10.5 (9.9 to 11.0)

SecondaryPercentage of Participants Seronegative at Baseline With Seroconversion as Compared to Baseline

Percentage of participants seronegative at baseline with Seroconversion (defined as \>4-fold titer change compared to baseline) by Visit Pooled by Trial Arm

Time frame:: at Day 15, Day 29, Day 85, Day 180 and Month 12
Reported as:: Count of participants · Participants

Percentage of Participants Seronegative at Baseline With Seroconversion as Compared to Baseline
Participants	VLA1553 Half Dose	VLA1553 Full Dose
Visit 4 - Day 15	95	110
Visit 5 - Day 29	98	111
Visit 6 - Day 85	94	110
Visit 7 - Day 180	96	111
Visit 8 - Day 365	95	110

SecondaryPercentage of Participants Seropositive at Baseline With Seroconversion as Compared to Baseline

Percentage of participants seropositive at baseline with Seroconversion (defined as \>4-fold titer change compared to baseline) by Visit Pooled by Trial Arm.

Time frame:: at Day 15, Day 29, Day 85, Day 180 and Month 12
Reported as:: Count of participants · Participants

Percentage of Participants Seropositive at Baseline With Seroconversion as Compared to Baseline
Participants	VLA1553 Half Dose	VLA1553 Full Dose	Control
Visit 4 - Day 15	0	0	0
Visit 5 - Day 29	0	0	0
Visit 6 - Day 85	0	0	0
Visit 7 - Day 180	0	0	1
Visit 8 - Day 365	0	0	0

SecondaryPercentage of Participants With Seroconversion as Compared to Baseline Stratified by Age Stratum

Percentage of participants with Seroconversion (defined as \>4-fold titer change compared to baseline) by Visit by Age Group and Trial Arm.

Time frame:: at Day 15, Day 29, Day 85, Day 180 and Month 12
Reported as:: Count of participants · Participants

Percentage of Participants With Seroconversion as Compared to Baseline Stratified by Age Stratum
Participants	VLA1553 Half Dose - 7-11 Years	VLA1553 Full Dose - 7-11 Years	VLA1553 Half Dose - 3-6 Years	VLA1553 Full Dose - 3-6 Years	VLA1553 Half Dose - 1-2 Years	VLA1553 Full Dose - 1-2 Years
Visit 4 - Day 15	26	36	36	38	31	35
Visit 5 - Day 29	26	36	37	38	33	35
Visit 6 - Day 85	26	35	35	38	30	36
Visit 7 - Day 180	26	36	38	38	30	36
Visit 8 - Day 365	26	36	37	38	30	35

SecondaryPercentage of Participants With Seroconversion as Compared to Baseline by Dose

Percentage of participants with Seroconversion (defined as \>4-fold titer change compared to baseline) by Visit Pooled by Trial Arm

Time frame:: at Day 15, Day 29, Day 85, Day 180 and Month 12
Reported as:: Count of participants · Participants

Percentage of Participants With Seroconversion as Compared to Baseline by Dose
Participants	VLA1553 Half Dose	VLA1553 Full Dose
Visit 4 - Day 15	93	109
Visit 5 - Day 29	96	109
Visit 6 - Day 85	91	109
Visit 7 - Day 180	94	110
Visit 8 - Day 365	93	109

SecondaryPercentage of Participants Seronegative at Baseline With a Seroresponse (Defined as PRNT50 ≥150 for Baseline Negative Participants) by Dose

Percentage of Participants with Seroresponse for CHIKV-Specific Neutralizing Antibody Titers (defined as PRNT50 ≥150) by Visit Pooled by Trial Arm.

Time frame:: on Day 15, Day 29, Day 85, Day 180 and Month 12 post-vaccination
Reported as:: Count of participants · Participants

Percentage of Participants Seronegative at Baseline With a Seroresponse (Defined as PRNT50 ≥150 for Baseline Negative Participants) by Dose
Participants	VLA1553 Half Dose	VLA1553 Full Dose
Visit 4 - Day 15	94	110
Visit 5 - Day 29	97	111
Visit 6 - Day 85	92	110
Visit 7 - Day 180	95	111
Visit 8 - Day 365	92	109

SecondaryPercentage of Participants With a Seroresponse Stratified by Age Stratum

Percentage of Participants with Seroresponse for CHIKV-Specific Neutralizing Antibody Titers (defined as PRNT50 ≥150) by Visit by Age Group and Trial Arm.

Time frame:: on Day 15, Day 29, Day 85, Day 180 and Month 12 post-vaccination
Reported as:: Count of participants · Participants

Percentage of Participants With a Seroresponse Stratified by Age Stratum
Participants	VLA1553 Half Dose - 7-11 Years	VLA1553 Full Dose - 7-11 Years	VLA1553 Half Dose - 3-6 Years	VLA1553 Full Dose - 3-6 Years	VLA1553 Half Dose - 1-2 Years	VLA1553 Full Dose - 1-2 Years
Visit 4 - Day 15	26	36	36	38	30	35
Visit 5 - Day 29	26	36	37	38	32	35
Visit 6 - Day 85	26	35	34	38	30	36
Visit 7 - Day 180	26	36	37	38	30	36
Visit 8 - Day 365	26	35	36	38	28	35

SecondaryPercentage of Participants With a Seroresponse Stratified by Dose

Percentage of Participants with Seroresponse for CHIKV-Specific Neutralizing Antibody Titers (defined as PRNT50 ≥150) by Visit Pooled by Trial Arm.

Time frame:: on Day 15, Day 29, Day 85, Day 180 and Month 12 post-vaccination
Reported as:: Count of participants · Participants

Percentage of Participants With a Seroresponse Stratified by Dose
Participants	VLA1553 Half Dose	VLA1553 Full Dose
Visit 4 - Day 15	92	109
Visit 5 - Day 29	95	109
Visit 6 - Day 85	90	109
Visit 7 - Day 180	93	110
Visit 8 - Day 365	90	108

SecondaryFold Change of CHIKV-specific Neutralizing Antibody Titers as Compared to Baseline in Participants Seronegative at Baseline

Fold Change for CHIKV-Specific Neutralizing Antibody Titers in seronegative Participants by Visit Pooled by Trial Arm.

Time frame:: at Days 15, 29, 85, 180 and at Month 12 post-vaccination
Reported as:: Geometric mean · fold change

Fold Change of CHIKV-specific Neutralizing Antibody Titers as Compared to Baseline in Participants Seronegative at Baseline
fold change	VLA1553 Half Dose	VLA1553 Full Dose	Control
Visit 4 - Day 15	103.6 (71.9 to 149.3)	195.0 (151.4 to 251.2)	1.0 (0.9 to 1.1)
Visit 5 - Day 29	182.8 (128.7 to 259.7)	286.1 (226.8 to 360.8)	1.0 (0.9 to 1.1)
Visit 6 - Day 85	62.5 (46.1 to 84.6)	103.1 (83.1 to 128.1)	1.0 (0.9 to 1.1)
Visit 7 - Day 180	50.9 (37.9 to 68.4)	81.4 (65.9 to 100.5)	1.0 (0.9 to 1.0)
Visit 8 - Day 365	79.1 (56.7 to 110.3)	135.6 (107.2 to 171.5)	1.0 (0.9 to 1.0)

SecondaryFold Change of CHIKV-specific Neutralizing Antibody Titers as Compared to Baseline in Seropositive Participants

Fold Change for CHIKV-Specific Neutralizing Antibody Titers in seropositive Participants by Visit Pooled by Trial Arm.

Time frame:: at Days 15, 29, 85, 180 and at Month 12 post-vaccination
Reported as:: Mean · fold change

Fold Change of CHIKV-specific Neutralizing Antibody Titers as Compared to Baseline in Seropositive Participants
fold change	VLA1553 Half Dose	VLA1553 Full Dose	Control
Visit 4 - Day 15	0.9 (0.7 to 1.1)	1.4 (0.8 to 2.5)	1.1 (0.6 to 2.2)
Visit 5 - Day 29	0.8 (0.6 to 1.1)	1.9 (1.4 to 2.7)	1.2 (0.9 to 1.8)
Visit 6 - Day 85	0.8 (0.6 to 1.2)	1.9 (1.4 to 2.6)	1.4 (0.9 to 2.2)
Visit 7 - Day 180	1.2 (0.8 to 1.8)	1.1 (0.7 to 1.6)	1.2 (0.6 to 2.1)
Visit 8 - Day 365	0.9 (0.6 to 1.3)	1.2 (0.6 to 2.4)	1.4 (0.8 to 2.2)

SecondaryFold Change of CHIKV-specific Neutralizing Antibody Titers as Compared to Baseline Stratified by Age Stratum

Fold Change for CHIKV-Specific Neutralizing Antibody Titers by Visit by Age Group and Trial Arm.

Time frame:: at Days 15, 29, 85, 180 and at Month 12 post-vaccination
Reported as:: Geometric mean · fold change

Fold Change of CHIKV-specific Neutralizing Antibody Titers as Compared to Baseline Stratified by Age Stratum
fold change	VLA1553 Half Dose - 7-11 Years	VLA1553 Full Dose - 7-11 Years	Control - 7-11 Years	VLA1553 Half Dose - 3-6 Years	VLA1553 Full Dose - 3-6 Years	Control - 3-6 Years	VLA1553 Half Dose - 1-2 Years	VLA1553 Full Dose - 1-2 Years	Control - 1-2 Years
Visit 4 - Day 15	83.6 (44.3 to 157.7)	221.4 (171.6 to 285.7)	0.9 (0.8 to 1.1)	140.0 (80.9 to 242.2)	227.5 (151.8 to 341.0)	1.0 (1.0 to 1.0)	96.0 (46.3 to 199.3)	147.5 (80.9 to 268.9)	1.0 (0.9 to 1.2)
Visit 5 - Day 29	197.9 (94.2 to 415.8)	344.4 (295.7 to 401.0)	0.9 (0.8 to 1.1)	211.5 (126.3 to 354.2)	313.5 (210.8 to 466.1)	1.0 (1.0 to 1.0)	143.9 (73.0 to 283.7)	216.2 (123.5 to 378.4)	1.1 (0.9 to 1.2)
Visit 6 - Day 85	63.4 (34.8 to 115.8)	124.1 (100.4 to 153.4)	0.9 (0.8 to 1.1)	74.2 (48.3 to 114.2)	107.4 (76.4 to 150.9)	1.0 (1.0 to 1.0)	51.7 (27.8 to 96.4)	83.1 (50.0 to 138.1)	1.0 (0.9 to 1.2)
Visit 7 - Day 180	57.4 (31.6 to 104.2)	83.5 (64.8 to 107.7)	0.9 (0.8 to 1.1)	45.6 (30.4 to 68.4)	87.2 (63.5 to 119.8)	1.0 (1.0 to 1.0)	50.6 (27.2 to 94.0)	82.0 (51.8 to 129.9)	1.0 (0.9 to 1.0)
Visit 8 - Day 365	69.3 (37.6 to 127.7)	145.1 (110.2 to 191.0)	1.0 (0.8 to 1.2)	83.7 (50.8 to 137.9)	138.2 (97.5 to 195.9)	1.0 (1.0 to 1.0)	81.4 (40.0 to 165.5)	124.3 (70.3 to 219.6)	1.0 (0.9 to 1.2)

SecondaryFold Change of CHIKV-specific Neutralizing Antibody Titers as Compared to Baseline Stratified by Dose

Fold Change for CHIKV-Specific Neutralizing Antibody Titers by Visit Pooled by Trial Arm.

Time frame:: at Days 15, 29, 85, 180 and at Month 12 post-vaccination
Reported as:: Geometric mean · fold change

Fold Change of CHIKV-specific Neutralizing Antibody Titers as Compared to Baseline Stratified by Dose
fold change	VLA1553 Half Dose	VLA1553 Full Dose	Control
Visit 4 - Day 15	106.3 (74.0 to 152.7)	194.5 (150.6 to 251.1)	1.0 (0.9 to 1.1)
Visit 5 - Day 29	181.2 (126.7 to 259.1)	284.4 (224.7 to 359.9)	1.0 (0.9 to 1.1)
Visit 6 - Day 85	62.5 (45.9 to 85.2)	102.6 (82.5 to 127.6)	1.0 (0.9 to 1.0)
Visit 7 - Day 180	50.4 (37.3 to 68.0)	84.3 (68.9 to 103.0)	1.0 (0.9 to 1.0)
Visit 8 - Day 365	78.7 (56.0 to 110.4)	135.3 (106.7 to 171.6)	1.0 (0.9 to 1.1)

SecondaryPercentage of Participants Seronegative at Baseline Reaching an at Least 4-fold, 8-fold, 16-fold or 64-fold Change in CHIKV-specific Neutralizing Antibody Titers Compared to Baseline

Percentage of Participants Reaching a 4-/8-/16-/64-Fold Change in Titers by Visit Pooled by Trial Arm.

Time frame:: at Day 15, Day 29, Day 85, Day 180 and Month 12
Reported as:: Count of participants · Participants

Percentage of Participants Seronegative at Baseline Reaching an at Least 4-fold, 8-fold, 16-fold or 64-fold Change in CHIKV-specific Neutralizing Antibody Titers Compared to Baseline
Participants	VLA1553 Half Dose	VLA1553 Full Dose
Visit 4 - Day 15: 4-fold change	95	110
Visit 4 - Day 15: 8-fold change	95	110
Visit 4 - Day 15: 16-fold change	94	110
Visit 4 - Day 15: 64-fold change	83	103
Visit 5 - Day 29: 4-fold change	98	111
Visit 5 - Day 29: 8-fold change	97	111
Visit 5 - Day 29: 16-fold change	97	111
Visit 5 - Day 29: 64-fold change	95	111
Visit 6 - Day 85: 4-fold change	94	110
Visit 6 - Day 85: 8-fold change	94	110
Visit 6 - Day 85: 16-fold change	92	110
Visit 6 - Day 85: 64-fold change	74	93
Visit 7 - Day 180: 4-fold change	96	111
Visit 7 - Day 180: 8-fold change	95	111
Visit 7 - Day 180: 16-fold change	94	111
Visit 7 - Day 180: 64-fold change	59	85
Visit 8 - Day 365: 4-fold change	95	110
Visit 8 - Day 365: 8-fold change	94	110
Visit 8 - Day 365: 16-fold change	91	109
Visit 8 - Day 365: 64-fold change	74	100

SecondaryPercentage of Participants Reaching an at Least 4-fold, 8-fold, 16-fold or 64-fold Change in CHIKV-specific Neutralizing Antibody Titers Compared to Baseline Stratified by Age Stratum

Percentage of Participants Reaching a 4-/8-/16-/64-Fold Change in Titers by Visit by Age Group and Trial Arm.

Time frame:: at Day 15, Day 29, Day 85, Day 180 and Month 12
Reported as:: Count of participants · Participants

Percentage of Participants Reaching an at Least 4-fold, 8-fold, 16-fold or 64-fold Change in CHIKV-specific Neutralizing Antibody Titers Compared to Baseline Stratified by Age Stratum
Participants	VLA1553 Half Dose - 7-11 Years	VLA1553 Full Dose - 7-11 Years	VLA1553 Half Dose - 3-6 Years	VLA1553 Full Dose - 3-6 Years	VLA1553 Half Dose - 1-2 Years	VLA1553 Full Dose - 1-2 Years
Visit 4 - Day 15: 4-fold change	26	36	36	38	31	35
Visit 4 - Day 15: 8-fold change	26	36	36	38	31	35
Visit 4 - Day 15: 16-fold change	26	36	36	38	30	35
Visit 4 - Day 15: 64-fold change	22	34	32	35	28	33
Visit 5 - Day 29: 4-fold change	26	36	37	38	33	35
Visit 5 - Day 29: 8-fold change	26	36	37	38	32	35
Visit 5 - Day 29: 16-fold change	26	36	37	38	32	35
Visit 5 - Day 29: 64-fold change	25	36	36	38	32	35
Visit 6 - Day 85: 4-fold change	26	35	35	38	30	36
Visit 6 - Day 85: 8-fold change	26	35	34	38	30	36
Visit 6 - Day 85: 16-fold change	26	35	34	38	30	36
Visit 6 - Day 85: 64-fold change	22	30	26	31	24	31
Visit 7 - Day 180: 4-fold change	26	36	38	38	30	36
Visit 7 - Day 180: 8-fold change	26	36	37	38	30	36
Visit 7 - Day 180: 16-fold change	26	36	36	38	30	36
Visit 7 - Day 180: 64-fold change	19	25	18	28	21	31
Visit 8 - Day 365: 4-fold change	26	36	37	38	30	35
Visit 8 - Day 365: 8-fold change	26	36	37	38	29	35
Visit 8 - Day 365: 16-fold change	26	35	35	38	28	35
Visit 8 - Day 365: 64-fold change	21	32	25	33	26	34

SecondaryPercentage of Participants Reaching an at Least 4-fold, 8-fold, 16-fold or 64-fold Change in CHIKV-specific Neutralizing Antibody Titers Compared to Baseline by Dose

Percentage of Participants Reaching a 4-/8-/16-/64-Fold Change in Titers by Visit Pooled by Trial Arm.

Time frame:: at Day 15, Day 29, Day 85, Day 180 and Month 12
Reported as:: Count of participants · Participants

Percentage of Participants Reaching an at Least 4-fold, 8-fold, 16-fold or 64-fold Change in CHIKV-specific Neutralizing Antibody Titers Compared to Baseline by Dose
Participants	VLA1553 Half Dose	VLA1553 Full Dose
Visit 4 - Day 15: 4-fold change	93	109
Visit 4 - Day 15: 8-fold change	93	109
Visit 4 - Day 15: 16-fold change	92	109
Visit 4 - Day 15: 64-fold change	82	102
Visit 5 - Day 29: 4-fold change	96	109
Visit 5 - Day 29: 8-fold change	95	109
Visit 5 - Day 29: 16-fold change	95	109
Visit 5 - Day 29: 64-fold change	93	109
Visit 6 - Day 85: 4-fold change	91	109
Visit 6 - Day 85: 8-fold change	91	109
Visit 6 - Day 85: 16-fold change	90	109
Visit 6 - Day 85: 64-fold change	72	92
Visit 7 - Day 180: 4-fold change	94	110
Visit 7 - Day 180: 8-fold change	93	110
Visit 7 - Day 180: 16-fold change	92	110
Visit 7 - Day 180: 64-fold change	58	84
Visit 8 - Day 365: 4-fold change	93	109
Visit 8 - Day 365: 8-fold change	92	109
Visit 8 - Day 365: 16-fold change	89	108
Visit 8 - Day 365: 64-fold change	72	99

Adverse events

Collected over - Up to 14 days post-vaccination: solicited local and systemic Adverse Events - Up to Month 6 and Month 12 post-vaccination: Unsolicited AEs - Up to Month 6 and Month 12 post-vaccination: SAEs - Within 2 to 21 days post-vaccination: early onset AESI - 22 days post-vaccination till trial end: late onset AESI. Non-serious events are listed at a 5% frequency threshold.

Adverse event summary by group
Group	Deaths	Serious	Other
VLA1553 Half Dose - 7-11 Years	0/40 (0%)	1/40 (2.5%)	27/40 (67.5%)
VLA1553 Full Dose - 7-11 Years	0/43 (0%)	2/43 (4.7%)	32/43 (74.4%)
Control - 7-11 Years	0/21 (0%)	0/21 (0%)	15/21 (71.4%)
VLA1553 Half Dose - 3-6 Years	0/40 (0%)	1/40 (2.5%)	29/40 (72.5%)
VLA1553 Full Dose - 3-6 Years	0/40 (0%)	0/40 (0%)	24/40 (60%)
Control - 3-6 Years	0/20 (0%)	0/20 (0%)	16/20 (80%)
VLA1553 Half Dose - 1-2 Years	0/39 (0%)	0/39 (0%)	28/39 (71.8%)
VLA1553 Full Dose - 1-2 Years	0/41 (0%)	2/41 (4.9%)	32/41 (78%)
Control - 1-2 Years	0/20 (0%)	1/20 (5%)	14/20 (70%)

Most frequent serious events

Most frequent serious events
Event	VLA1553 Half Dose - 7-11 Years	VLA1553 Full Dose - 7-11 Years	Control - 7-11 Years	VLA1553 Half Dose - 3-6 Years	VLA1553 Full Dose - 3-6 Years	Control - 3-6 Years	VLA1553 Half Dose - 1-2 Years	VLA1553 Full Dose - 1-2 Years	Control - 1-2 Years
PneumoniaInfections and infestations	0/40	0/43	0/21	0/40	0/40	0/20	0/39	0/41	1/20
CellulitisInfections and infestations	1/40	0/43	0/21	0/40	0/40	0/20	0/39	0/41	0/20
Appendicitis perforatedInfections and infestations	0/40	0/43	0/21	1/40	0/40	0/20	0/39	0/41	0/20
Asthmatic crisisRespiratory, thoracic and mediastinal disorders	0/40	1/43	0/21	0/40	0/40	0/20	0/39	1/41	0/20
Drug hypersensitivityImmune system disorders	0/40	0/43	0/21	0/40	0/40	0/20	0/39	1/41	0/20
FaecalomaGastrointestinal disorders	0/40	1/43	0/21	0/40	0/40	0/20	0/39	0/41	0/20

Most frequent other events

Most frequent other events
Event	VLA1553 Half Dose - 7-11 Years	VLA1553 Full Dose - 7-11 Years	Control - 7-11 Years	VLA1553 Half Dose - 3-6 Years	VLA1553 Full Dose - 3-6 Years	Control - 3-6 Years	VLA1553 Half Dose - 1-2 Years	VLA1553 Full Dose - 1-2 Years	Control - 1-2 Years
NasopharyngitisInfections and infestations	17/40	18/43	6/21	19/40	14/40	10/20	24/39	27/41	11/20
HeadacheNervous system disorders	14/40	15/43	5/21	5/40	7/40	3/20	0/39	0/41	0/20
Injection site painGeneral disorders	12/40	8/43	6/21	5/40	7/40	0/20	2/39	1/41	1/20
DiarrhoeaGastrointestinal disorders	1/40	3/43	0/21	2/40	1/40	2/20	3/39	7/41	5/20
Viral infectionInfections and infestations	0/40	1/43	5/21	3/40	3/40	3/20	3/39	4/41	1/20
PyrexiaGeneral disorders	7/40	6/43	1/21	8/40	6/40	4/20	9/39	7/41	1/20
Rhinitis allergicRespiratory, thoracic and mediastinal disorders	4/40	3/43	1/21	2/40	2/40	3/20	5/39	8/41	4/20
VomitingGastrointestinal disorders	1/40	3/43	0/21	4/40	4/40	2/20	3/39	5/41	1/20

Baseline characteristics

Age, Continuous
Age, Continuous(years)	VLA1553 Half Dose	VLA1553 Full Dose	Control	Total
Mean	5.0 ± 3.05	5.0 ± 3.05	5.1 ± 3.37	5.0 ± 3.11

Sex: Female, Male
Sex: Female, Male(Participants)	VLA1553 Half Dose	VLA1553 Full Dose	Control	Total
Female	52	65	29	146
Male	67	59	32	158

Race/Ethnicity, Customized
Race/Ethnicity, Customized(Participants)	VLA1553 Half Dose	VLA1553 Full Dose	Control	Total
American Indian or Alaska Native	0	2	0	2
Asian	0	0	0	0
Black or African American	42	34	12	88
White	0	1	0	1
Other	77	87	49	213

Study locations

3 sites

Fundacion Dominicana de Perinatologia Fundacion Probebe
Santo Domingo, Gazcue, Dominican Republic
Instituto Dermatologico y Cirugia de la Piel "Dr Huberto Bogaert Diaz" IDCP
Santo Domingo, 10306, Dominican Republic
Inversiones en Investigacion Medica INVERIME
Tegucigalpa, Honduras

References and documents

Publications

Weisova P, Scheiblauer S, Ecker J, Schneider M, Hochreiter R, Bitzer A, Kosulin K, Schoengrundner P, Fuchs U, Rodeles L, Mazara S, Donastorg Y, Rivera S, Wressnigg N, Dubischar K, Buerger V, Eder-Lingelbach S, Jaramillo JC. Live-attenuated chikungunya vaccine in children: a randomized phase 2 trial. Nat Med. 2026 Feb;32(2):561-571. doi: 10.1038/s41591-025-04197-2. Epub 2026 Feb 6. PubMed 41652122 ↗

Study documents

Study protocol ↗ · Feb 1, 2024
Statistical analysis plan ↗ · Sep 10, 2025

PDFs hosted by the registry, ClinicalTrials.gov.

Individual participant data

Plan to share: Yes — After trial completion, Valneva may provide access to individual de-identified participant data and related trial documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Trial Report (CTR)) upon request from qualified researchers, and subject to Valneva's review and approval.

Updates

Tracking since Sep 25, 2026

No changes since tracking began. The registry record was last updated on Aug 13, 2026, before this site started recording changes on Sep 25, 2026. Its history is on ClinicalTrials.gov ↗

Registry details

Key details

Study ID: NCT06106581
Lead sponsor: Valneva Austria GmbH
Responsible party: Sponsor
First posted: Oct 30, 2023
Start date: Dec 18, 2023
Primary completion: Jul 31, 2024
Completion: Jul 2, 2025
Results posted: Aug 13, 2026
Last update: Aug 13, 2026

Study contacts

Valneva Clinical Development

study chair · Valneva Austria GmbH

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 Aug 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.

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.

Studies of the drug tested here: Chikungunya vaccine

Other studies in this condition

Chikungunya Fever →

Other studies from this sponsor

Valneva Austria GmbH →

Start the discussion