Trial Outcomes & Findings for Study on a Live-attenuated Respiratory Syncytial Virus Vaccine for Assessment of Safety, Transmissibility, and Genetic Stability of the Vaccine Virus Among Close Contacts in Infants and Toddlers 6 to < 24 Months of Age in Puerto Rico (USA) (NCT NCT05687279)
NCT ID: NCT05687279
Last Updated: 2026-01-26
Results Overview
Nasal swabs were collected to assess the presence of vaccine virus after first vaccination. Vaccine virus transmission was defined as presence of detected vaccine virus confirmed by RSVt quantitative reverse transcription polymerase chain reaction (qRT-PCR) assay (vaccine virus shedding \>=lower limit of detection \[LOD=2.80 log10 copies/mL\]) in pediatric participants receiving placebo. Percentages are rounded off to the tenth decimal place.
COMPLETED
PHASE1/PHASE2
80 participants
Pre-vaccination on Day 1 and post-vaccination on Days 4, 8, 11, 15, 18 and 22
2026-01-26
Participant Flow
The study was conducted at 3 sites in Puerto Rico from 06-Feb-2023 to 27-Dec-2024.
A total of 80 healthy infants/toddlers 6 to \<24 months of age were randomized in contact groups of 2-3 in a 1:1 ratio to receive 2 administrations 56 days apart of either live-attenuated respiratory syncytial virus delta (Δ) non-structural (NS)2/Δ1313/I1314L vaccine (RSVt vaccine) or placebo.
Participant milestones
| Measure |
RSVt
Participants received RSVt vaccine 0.2 milliliter (mL) as intranasal administration on Days 1 and 57
|
Placebo
Participants received placebo 0.2 mL as intranasal administration in contact groups with RSVt vaccine recipients on Days 1 and 57
|
|---|---|---|
|
Overall Study
STARTED
|
40
|
40
|
|
Overall Study
COMPLETED
|
35
|
38
|
|
Overall Study
NOT COMPLETED
|
5
|
2
|
Reasons for withdrawal
Withdrawal data not reported
Baseline Characteristics
Study on a Live-attenuated Respiratory Syncytial Virus Vaccine for Assessment of Safety, Transmissibility, and Genetic Stability of the Vaccine Virus Among Close Contacts in Infants and Toddlers 6 to < 24 Months of Age in Puerto Rico (USA)
Baseline characteristics by cohort
| Measure |
RSVt
n=40 Participants
Participants received RSVt vaccine 0.2 milliliter (mL) as intranasal administration on Days 1 and 57
|
Placebo
n=40 Participants
Participants received placebo 0.2 milliliter (mL) as intranasal administration in contact groups with RSVt vaccine recipients on Days 1 and 57
|
Total
n=80 Participants
Total of all reporting groups
|
|---|---|---|---|
|
Age, Categorical
<=18 years
|
40 Participants
n=25 Participants
|
40 Participants
n=25 Participants
|
80 Participants
n=50 Participants
|
|
Age, Categorical
Between 18 and 65 years
|
0 Participants
n=25 Participants
|
0 Participants
n=25 Participants
|
0 Participants
n=50 Participants
|
|
Age, Categorical
>=65 years
|
0 Participants
n=25 Participants
|
0 Participants
n=25 Participants
|
0 Participants
n=50 Participants
|
|
Age, Continuous
|
15.1 months
STANDARD_DEVIATION 5.55 • n=25 Participants
|
15.8 months
STANDARD_DEVIATION 5.81 • n=25 Participants
|
15.4 months
STANDARD_DEVIATION 5.66 • n=50 Participants
|
|
Sex: Female, Male
Female
|
16 Participants
n=25 Participants
|
23 Participants
n=25 Participants
|
39 Participants
n=50 Participants
|
|
Sex: Female, Male
Male
|
24 Participants
n=25 Participants
|
17 Participants
n=25 Participants
|
41 Participants
n=50 Participants
|
|
Race (NIH/OMB)
American Indian or Alaska Native
|
0 Participants
n=25 Participants
|
1 Participants
n=25 Participants
|
1 Participants
n=50 Participants
|
|
Race (NIH/OMB)
Asian
|
0 Participants
n=25 Participants
|
0 Participants
n=25 Participants
|
0 Participants
n=50 Participants
|
|
Race (NIH/OMB)
Native Hawaiian or Other Pacific Islander
|
0 Participants
n=25 Participants
|
0 Participants
n=25 Participants
|
0 Participants
n=50 Participants
|
|
Race (NIH/OMB)
Black or African American
|
1 Participants
n=25 Participants
|
2 Participants
n=25 Participants
|
3 Participants
n=50 Participants
|
|
Race (NIH/OMB)
White
|
29 Participants
n=25 Participants
|
27 Participants
n=25 Participants
|
56 Participants
n=50 Participants
|
|
Race (NIH/OMB)
More than one race
|
10 Participants
n=25 Participants
|
10 Participants
n=25 Participants
|
20 Participants
n=50 Participants
|
|
Race (NIH/OMB)
Unknown or Not Reported
|
0 Participants
n=25 Participants
|
0 Participants
n=25 Participants
|
0 Participants
n=50 Participants
|
PRIMARY outcome
Timeframe: Pre-vaccination on Day 1 and post-vaccination on Days 4, 8, 11, 15, 18 and 22Population: The safety analysis set included those pediatric participants who received at least 1 study vaccine administration. Only those participants with data collected at specified timepoints are reported.
Nasal swabs were collected to assess the presence of vaccine virus after first vaccination. Vaccine virus transmission was defined as presence of detected vaccine virus confirmed by RSVt quantitative reverse transcription polymerase chain reaction (qRT-PCR) assay (vaccine virus shedding \>=lower limit of detection \[LOD=2.80 log10 copies/mL\]) in pediatric participants receiving placebo. Percentages are rounded off to the tenth decimal place.
Outcome measures
| Measure |
Placebo
n=36 Participants
Participants received placebo 0.2 milliliter (mL) as intranasal administration in contact groups with RSVt vaccine recipients on Days 1 and 57
|
Placebo
Participants received placebo 0.2 milliliter (mL) as intranasal administration in contact groups with RSVt vaccine recipients on Days 1 and 57
|
|---|---|---|
|
Percentage of Placebo Receiving Pediatric Participants With Vaccine Virus Detected in Nasal Swabs After the First Vaccination
Day 8
|
0 percentage of participants
Interval 0.0 to 9.7
|
—
|
|
Percentage of Placebo Receiving Pediatric Participants With Vaccine Virus Detected in Nasal Swabs After the First Vaccination
Day 1
|
0 percentage of participants
Interval 0.0 to 10.9
|
—
|
|
Percentage of Placebo Receiving Pediatric Participants With Vaccine Virus Detected in Nasal Swabs After the First Vaccination
Day 4
|
0 percentage of participants
Interval 0.0 to 9.7
|
—
|
|
Percentage of Placebo Receiving Pediatric Participants With Vaccine Virus Detected in Nasal Swabs After the First Vaccination
Day 11
|
0 percentage of participants
Interval 0.0 to 9.7
|
—
|
|
Percentage of Placebo Receiving Pediatric Participants With Vaccine Virus Detected in Nasal Swabs After the First Vaccination
Day 15
|
0 percentage of participants
Interval 0.0 to 10.0
|
—
|
|
Percentage of Placebo Receiving Pediatric Participants With Vaccine Virus Detected in Nasal Swabs After the First Vaccination
Day 18
|
0 percentage of participants
Interval 0.0 to 9.7
|
—
|
|
Percentage of Placebo Receiving Pediatric Participants With Vaccine Virus Detected in Nasal Swabs After the First Vaccination
Day 22
|
0 percentage of participants
Interval 0.0 to 10.3
|
—
|
PRIMARY outcome
Timeframe: Pre-vaccination on Day 1 and post-vaccination on Days 4, 8, 11, 15, 18, 22, 64 and 71Population: The safety analysis set included those pediatric participants who received at least 1 study vaccine administration. Only participants with quantified virus shedding at specified timepoints are reported.
Nasal swabs were collected to assess the shedding of the attenuated RSV vaccine strain and quantified by RSVt qRT PCR assay. Quantified virus shedding was defined as vaccine virus shedding \>=lower limit of quantification (LLOQ=3.37 log10 copies/mL).
Outcome measures
| Measure |
Placebo
n=7 Participants
Participants received placebo 0.2 milliliter (mL) as intranasal administration in contact groups with RSVt vaccine recipients on Days 1 and 57
|
Placebo
Participants received placebo 0.2 milliliter (mL) as intranasal administration in contact groups with RSVt vaccine recipients on Days 1 and 57
|
|---|---|---|
|
Titer of Vaccine Virus Shedding in All Pediatric Participants Detected in Nasal Swabs
Day 8
|
4.33 log10 copies/mL
Standard Deviation 0.649
|
—
|
|
Titer of Vaccine Virus Shedding in All Pediatric Participants Detected in Nasal Swabs
Day 64
|
3.55 log10 copies/mL
Standard Deviation 0.014
|
—
|
|
Titer of Vaccine Virus Shedding in All Pediatric Participants Detected in Nasal Swabs
Day 11
|
4.33 log10 copies/mL
Standard Deviation 0.617
|
—
|
|
Titer of Vaccine Virus Shedding in All Pediatric Participants Detected in Nasal Swabs
Day 22
|
4.72 log10 copies/mL
|
—
|
PRIMARY outcome
Timeframe: Up to 21 days after each vaccination (Day 1 to Day 22 and Day 57 to Day 78)Population: The safety analysis set included those pediatric participants who received at least 1 study vaccine administration. Only participants with detected virus shedding were included in this analysis.
Nasal swabs were collected to identify the difference in genetic sequence of mutated vaccine virus segments compared to the reference strain vaccine virus isolates in the vaccine virus positive swabs from pediatric participants receiving placebo after each vaccination. Detected virus shedding was defined as vaccine virus shedding \>=LOD (2.80 log10 copies/mL).
Outcome measures
Outcome data not reported
SECONDARY outcome
Timeframe: Pre-vaccination on Day 1 (first vaccination) and Day 57 (second vaccination) and up to 28 days after second vaccination, Day 85Population: The full analysis set included a subset of randomized pediatric participants who received at least 1 study vaccine administration. Only those participants with data collected at specified timepoints are reported.
Serum samples were collected at specified timepoints for immunogenicity assessments. RSV A serum neutralizing antibody titers were evaluated by microneutralization (MN) assay.
Outcome measures
| Measure |
Placebo
n=38 Participants
Participants received placebo 0.2 milliliter (mL) as intranasal administration in contact groups with RSVt vaccine recipients on Days 1 and 57
|
Placebo
n=38 Participants
Participants received placebo 0.2 milliliter (mL) as intranasal administration in contact groups with RSVt vaccine recipients on Days 1 and 57
|
|---|---|---|
|
Geometric Mean Titers (GMTs) of RSV A Serum Neutralizing Antibody (nAb) Titers
Day 1
|
53.4 1/dilution
Interval 29.7 to 95.9
|
47.9 1/dilution
Interval 25.2 to 90.8
|
|
Geometric Mean Titers (GMTs) of RSV A Serum Neutralizing Antibody (nAb) Titers
Day 57
|
167 1/dilution
Interval 95.5 to 294.0
|
65.3 1/dilution
Interval 30.8 to 138.0
|
|
Geometric Mean Titers (GMTs) of RSV A Serum Neutralizing Antibody (nAb) Titers
Day 85
|
219 1/dilution
Interval 126.0 to 382.0
|
60.0 1/dilution
Interval 26.6 to 135.0
|
SECONDARY outcome
Timeframe: Pre-vaccination on Day 1 (first vaccination) and Day 57 (second vaccination) and up to 28 days after second vaccination, Day 85Population: The full analysis set included a subset of randomized pediatric participants who received at least 1 study vaccine administration. Only those participants with data collected at specified timepoints are reported.
Serum samples were collected at specified timepoints for immunogenicity assessments. Antibodies to RSV F antigen were measured using the anti RSV F IgG ELISA method.
Outcome measures
| Measure |
Placebo
n=38 Participants
Participants received placebo 0.2 milliliter (mL) as intranasal administration in contact groups with RSVt vaccine recipients on Days 1 and 57
|
Placebo
n=38 Participants
Participants received placebo 0.2 milliliter (mL) as intranasal administration in contact groups with RSVt vaccine recipients on Days 1 and 57
|
|---|---|---|
|
Secondary: Geometric Mean Titers of RSV Serum Anti-F Immunoglobulin G (IgG) Enzyme-linked Immuno-adsorbant Assay (ELISA) Antibody
Day 85
|
383 Elisa Units/mL
Interval 205.0 to 714.0
|
129 Elisa Units/mL
Interval 52.6 to 317.0
|
|
Secondary: Geometric Mean Titers of RSV Serum Anti-F Immunoglobulin G (IgG) Enzyme-linked Immuno-adsorbant Assay (ELISA) Antibody
Day 1
|
92.2 Elisa Units/mL
Interval 45.5 to 187.0
|
85.6 Elisa Units/mL
Interval 39.3 to 186.0
|
|
Secondary: Geometric Mean Titers of RSV Serum Anti-F Immunoglobulin G (IgG) Enzyme-linked Immuno-adsorbant Assay (ELISA) Antibody
Day 57
|
249 Elisa Units/mL
Interval 130.0 to 475.0
|
115 Elisa Units/mL
Interval 49.7 to 265.0
|
SECONDARY outcome
Timeframe: Up to 30 minutes after each vaccination (Days 1 and 57)Population: The safety analysis set included those pediatric participants who received at least 1 study vaccine administration.
An AE was any untoward medical occurrence in a clinical study participant temporally associated with the use of study vaccine, whether or not considered related to the study vaccine. An unsolicited AE was an observed AE that did not fulfill the conditions of solicited reactions, i.e., pre-listed in the case report form (CRF) in terms of diagnosis and onset window post-vaccination. All participants were observed for 30 minutes after each vaccination and any unsolicited AEs that occurred during that time were recorded as immediate unsolicited AEs.
Outcome measures
| Measure |
Placebo
n=39 Participants
Participants received placebo 0.2 milliliter (mL) as intranasal administration in contact groups with RSVt vaccine recipients on Days 1 and 57
|
Placebo
n=39 Participants
Participants received placebo 0.2 milliliter (mL) as intranasal administration in contact groups with RSVt vaccine recipients on Days 1 and 57
|
|---|---|---|
|
Number of Participants With Immediate Unsolicited Adverse Events (AEs)
|
0 Participants
|
0 Participants
|
SECONDARY outcome
Timeframe: Up to 21 days after each vaccination (Day 1 to Day 22 and Day 57 to Day 78)Population: The safety analysis set included those pediatric participants who received at least 1 study vaccine administration.
A solicited reaction was an expected adverse reaction (AR) (sign or symptom) observed and reported under the conditions (nature and onset) pre-listed in the protocol and CRF and considered as related to the study vaccine administered. An administration site reaction was an AR at and around the administration/injection site and were commonly inflammatory reactions. Solicited systemic reactions were systemic AEs and those occurring during the specified collection period were always considered related to the vaccine even if there was evidence of alternative etiology.
Outcome measures
| Measure |
Placebo
n=39 Participants
Participants received placebo 0.2 milliliter (mL) as intranasal administration in contact groups with RSVt vaccine recipients on Days 1 and 57
|
Placebo
n=39 Participants
Participants received placebo 0.2 milliliter (mL) as intranasal administration in contact groups with RSVt vaccine recipients on Days 1 and 57
|
|---|---|---|
|
Number of Participants With Solicited Administration Site Reactions and Systemic Reactions
Solicited administration site reaction
|
30 Participants
|
32 Participants
|
|
Number of Participants With Solicited Administration Site Reactions and Systemic Reactions
Solicited systemic reaction
|
26 Participants
|
25 Participants
|
SECONDARY outcome
Timeframe: Up to 28 days after each vaccination (Day 1 to Day 29 and Day 57 to Day 85)Population: The safety analysis set included those pediatric participants who received at least 1 study vaccine administration.
An AE was any untoward medical occurrence in a clinical study participant temporally associated with the use of study vaccine, whether or not considered related to the study vaccine. An unsolicited AE was an observed AE that did not fulfill the conditions of solicited reactions, that is, pre-listed in the CRF in terms of diagnosis and onset window post-vaccination.
Outcome measures
| Measure |
Placebo
n=39 Participants
Participants received placebo 0.2 milliliter (mL) as intranasal administration in contact groups with RSVt vaccine recipients on Days 1 and 57
|
Placebo
n=39 Participants
Participants received placebo 0.2 milliliter (mL) as intranasal administration in contact groups with RSVt vaccine recipients on Days 1 and 57
|
|---|---|---|
|
Number of Participants With Unsolicited Adverse Events
|
8 Participants
|
12 Participants
|
Adverse Events
RSVt
Placebo
Serious adverse events
| Measure |
RSVt
n=39 participants at risk
Participants received RSVt vaccine 0.2 milliliter (mL) as intranasal administration on Days 1 and 57
|
Placebo
n=39 participants at risk
Participants received placebo 0.2 milliliter (mL) as intranasal administration in contact groups with RSVt vaccine recipients on Days 1 and 57
|
|---|---|---|
|
Infections and infestations
Gastroenteritis
|
0.00%
0/39 • From date of first vaccination (Day 1) up to 6 months after the last study vaccination, approximately 237 days
Analysis was performed on the safety analysis set
|
2.6%
1/39 • Number of events 1 • From date of first vaccination (Day 1) up to 6 months after the last study vaccination, approximately 237 days
Analysis was performed on the safety analysis set
|
|
Infections and infestations
Influenza
|
2.6%
1/39 • Number of events 1 • From date of first vaccination (Day 1) up to 6 months after the last study vaccination, approximately 237 days
Analysis was performed on the safety analysis set
|
0.00%
0/39 • From date of first vaccination (Day 1) up to 6 months after the last study vaccination, approximately 237 days
Analysis was performed on the safety analysis set
|
|
Infections and infestations
Oral Herpes
|
0.00%
0/39 • From date of first vaccination (Day 1) up to 6 months after the last study vaccination, approximately 237 days
Analysis was performed on the safety analysis set
|
2.6%
1/39 • Number of events 1 • From date of first vaccination (Day 1) up to 6 months after the last study vaccination, approximately 237 days
Analysis was performed on the safety analysis set
|
|
Infections and infestations
Bronchiolitis
|
5.1%
2/39 • Number of events 2 • From date of first vaccination (Day 1) up to 6 months after the last study vaccination, approximately 237 days
Analysis was performed on the safety analysis set
|
5.1%
2/39 • Number of events 2 • From date of first vaccination (Day 1) up to 6 months after the last study vaccination, approximately 237 days
Analysis was performed on the safety analysis set
|
Other adverse events
| Measure |
RSVt
n=39 participants at risk
Participants received RSVt vaccine 0.2 milliliter (mL) as intranasal administration on Days 1 and 57
|
Placebo
n=39 participants at risk
Participants received placebo 0.2 milliliter (mL) as intranasal administration in contact groups with RSVt vaccine recipients on Days 1 and 57
|
|---|---|---|
|
Metabolism and nutrition disorders
Decreased Appetite
|
28.2%
11/39 • Number of events 14 • From date of first vaccination (Day 1) up to 6 months after the last study vaccination, approximately 237 days
Analysis was performed on the safety analysis set
|
35.9%
14/39 • Number of events 15 • From date of first vaccination (Day 1) up to 6 months after the last study vaccination, approximately 237 days
Analysis was performed on the safety analysis set
|
Additional Information
Results disclosure agreements
- Principal investigator is a sponsor employee The Sponsor must have the opportunity to review at least 60 days prior to submission for publication or presentation. If review indicates that potentially patentable subject matter would be disclosed, publication or public disclosure may be delayed for a maximum of an additional 60 days to allow for filing the necessary patent applications.
- Publication restrictions are in place
Restriction type: OTHER