Respiratory Syncytial VirusesCASSATTNCT06813872

Effectiveness of ABRYSVO® Maternal Respiratory Syncytial Virus (RSV) Vaccine Against RSV in Infants in Western Pennsylvania

An observational study of Respiratory Syncytial Viruses, run by Pfizer at 1 site in United States.

Active, not recruiting

Under way, not looking for participants. Everyone needed has enrolled. The study is still running.

Official record

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Trial summary

Who is it for?: Ages 0 to 6 months
Conditions the study is for: Respiratory Syncytial Viruses
What is being tested?: ABRYSVO Vaccination
Type of treatment: Vaccines
How many people: 1 participants
Where: 1 siteUnited States
Study dates: 24 Feb 2025to 31 Jul 2027
Phase: Observational
Are there results?: Not yet: the study is under way

Key requirements

Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.

Ages 0 to 6 months
All sexes
No healthy volunteers
Child

Study population: The study population will include infants who were hospitalized with ARI, have documented RSV test results and born to an individual eligible for ABRYSVO vaccination in pregnancy based on the timing of birth relative to the local seasonal ABRYSVO vaccination program.

Population included in ABYRSVO VE analyses:

Infants ≤ 6 months (≤ 180 days) of age on the index date.
Index date within the time period for data collection (approximately 01 October to 15 April in the 2023-2024, 2024-2025, 2025-2026, and 2026-2027 RSV seasons).
Infants born at ≥32 weeks of gestation.
Infants born to individuals who were expected (based on estimated date of delivery) to reach the indicated ABRYSVO vaccination window (320/7 to 366/7 weeks' gestation) during the local vaccination season.
Infant's EHR links to the maternal EHR.
Hospitalized at a UPMC facility during the RSV season (according to local hospital epidemiology) with acute respiratory tract illness symptoms meeting the protocol-defined clinical case, and for whom RSV testing results from a specimen collected 10 days prior to hospital admission through 3 days after hospital admission are known.
Ability to document maternal ABRYSVO receipt or not.

Population excluded from ABYRSVO VE analyses:

Infants who received any licensed or investigational RSV preventive product (e.g., RSV monoclonal antibodies, RSV vaccine (including investigational products or due to medication error)) since birth.
Born to birth parent for whom ABRYSVO vaccination status cannot be verified in the maternal EHR or Pennsylvania Immunization Electronic Registry System (PIERS) system.
Infants who were born to an individual vaccinated with ABRYSVO prior to the current pregnancy or vaccinated with more than one dose of ABRYSVO or vaccinated with any other licensed or investigational RSV vaccine during pregnancy.

Trial locations and contacts

1 site in 1 country.

United States1 site

Pfizer
New York, New York, 10001

Other trials in United States

About this study

Globally, respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract disease (LRTD) in infants and children. Pfizer has developed ABRYSVO-a bivalent RSV prefusion F protein-based vaccine (RSVpreF) composed of two prefusion F proteins to protect against both RSV-A and RSV-B. In the United States, ABRYSVO has been approved and recommended for active immunization of pregnant individuals from 320/7 to 366/7 weeks' gestational age for the prevention of LRTD and severe LRTD caused by RSV in infants from birth through 6 months of age. Post-licensure data from the United States and Argentina have also demonstrated real world effectiveness. Data from the US VISION and NVSN networks reported 79% (95% CI 55-90) and 70% (95% CI 28-88%) VE respectively against RSV-associated hospitalization among infants in the second RSV season and a study from Argentina reported 78.6% (95% CI 62.1-87.9) and 71.3% (95% CI 53.3-82.3) VE against RSV-associated LRTD leading to hospitalization among infants aged 0 to ≤3 and 0 to ≤6 months respectively.

To generate critical evidence to support vaccine policy and implementation, Pfizer will collaborate with University of Pittsburgh to study vaccine effectiveness (VE) of ABRYSVO vaccination during pregnancy against RSV-associated outcomes in infants. The study will take place in a real-world population in Western Pennsylvania over multiple seasons, beginning in the 2023-2024 season, and will use a test negative design (TND) approach.

There will be no active enrollment of study participants, no direct contact with study participants, and no collection of any primary data outside of the Standard of Care (SOC).

This study will use a TND to evaluate real-world VE of maternal ABRYSVO against RSV-associated outcomes in infants. Additionally, we will describe RSV-associated medically-attended visits for infants exposed to ABRYSVO and RSV monoclonal antibodies (e.g., Beyfortus and Enflonsia).

Conditions: Respiratory Syncytial Viruses
Being tested: ABRYSVO Vaccination

What participants receive

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

ABRYSVO VaccinationBiological
The primary exposure of interest for the TND study is maternal history of vaccination with Pfizer's ABRYSVO vaccine during pregnancy with the infant who presented for care. Infants will be considered "exposed to ABRYSVO" if their birth parent has documented evidence of receiving ABRYSVO ≥14 days before the date of the infant's birth, during the licensed gestational age window of 32 0/7 to 36 6/7 weeks.

Study groups in NCT06813872
Study group	Role	What they receive
Case		Cases for the primary objective will be infants meeting the outcome definition who had any positive laboratory-confirmed RSV test from a respiratory sample collected within 10 days prior to hospital admission through 3 days after hospital admission. Receives: Biological: ABRYSVO Vaccination
Control		Controls for the primary objective will be infants meeting the outcome definition who had a laboratory-confirmed negative RSV test from a respiratory sample collected within 10 days prior to hospital admission through 3 days after hospital admission. Receives: Biological: ABRYSVO Vaccination

What is being measured

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

RSV-positive ARI hospitalization confirmed by ³1 ARI symptom, laboratory testing, and hospitalization occurring 0 to ≤ 90 days of life during RSV season based on local epidemiology.
Measured: 0 to ≤ 90 days of life

Secondary outcomes (7)

RSV-positive ARI hospitalization confirmed by ³1 ARI symptom, laboratory testing, and hospitalization occurring 0 to ≤ 180 days of life during RSV season based on local epidemiology.
Measured: 0 to ≤180 days of life
RSV-positive ARI hospitalization confirmed by ≥ 1 ARI symptom, laboratory testing, and hospitalization occurring 91 to ≤180 days of life during the RSV season based on local epidemiology
Measured: 91 to ≤180 days of life
RSV-positive ARI hospitalization with study-defined LRTD occurring 0 to ≤ 90 days of life during RSV season based on local epidemiology.
Measured: 0 to ≤90 days of life
RSV-positive hospitalization with study-defined LRTD occurring 0 to ≤180 days of life during the RSV season based on local epidemiology.
Measured: 0 to ≤180 days of life
RSV-positive ARI hospitalization with study-defined LRTD occurring 91 to ≤ 180 days of life during RSV season based on local epidemiology.
Measured: 91 to ≤ 180 days of life
Number, age and characteristics of infants whose birth parent received ABRYSVO during pregnancy who present for a medical visit (outpatient, urgent care, emergency room, hospital) and have laboratory confirmed RSV between 0 to ≤ 90 days of life
Measured: 0 to ≤90 days of life
Number, age and characteristics of infants who received Beyfortus or Enflonsia between 0 to <7 days of life who present for a medical visit and have laboratory confirmed RSV between 1 to ≤ 96 days post-B
Measured: 1 to ≤96 days post-Beyfortus/Enflonsia exposure

Timeline

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

24 Feb 202531 Jul 2027

First posted7 Feb 2025
Study start24 Feb 2025
Primary completion31 Jul 2027 (estimated)
Study completion31 Jul 2027 (estimated)

Resources

Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
Other trials for Respiratory Syncytial VirusesStudies of the same condition, open and under way.
More trials run by PfizerThe sponsor's other registered studies.
What the trial phases meanHow a treatment moves from first tests in people to approval.

More details

For doctors and researchers: how the study is designed, who runs it, and its registry IDs.

Study design

Study type: Observational
Observational model: Case-control
Time perspective: Retrospective
Enrolment: 1 participants (actual)

IDs, dates and publications

ClinicalTrials.gov ID: NCT06813872
Sponsor's protocol ID: C3671074
Other IDs: CASSATT
Acronym: CASSATT
Status last verified: Jan 2026
First submitted: 31 Jan 2025
Last updated: 3 Feb 2026
Results posted: No
Data monitoring committee: No
Individual data sharing: No: Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical\_trials/trial\_data\_and\_results/data\_requests.

Want to know more?

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

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

Questions to ask the study team

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

See locations

RecruitingPhase 3
Study to Learn About a Respiratory Syncytial Virus Vaccine in Children at High Risk of RSV Disease
Respiratory Syncytial Virus (RSV)
Active, not recruitingPhase 3
A Study on the Immune Response and Safety of Vaccine Against Respiratory Syncytial Virus Given to Chinese Adults 18 to 59 Years of Age at Increased Risk of Respiratory Syncytial Virus Disease
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Active, not recruitingPhase 1
A Phase 1 Study to Evaluate JCXH-108, an mRNA-based Vaccine Against RSV
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RecruitingPhase 2
Immunogenicity of RSVPreF3 Vaccine in Immunocompromised Persons
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TARSILA Real-World Evidence Study
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All Respiratory Syncytial Viruses trials

Study at a glance

From the registry record, last updated by the sponsor on 3 Feb 2026. Recruitment status is as the sponsor reported it: confirm with the study team.

Official title: Effectiveness of ABRYSVO® Maternal Respiratory Syncytial Virus (RSV) Vaccine Against RSV in Infants in Western Pennsylvania
ClinicalTrials.gov ID: NCT06813872
Acronym / sponsor ID: CASSATT / C3671074
Conditions: Respiratory Syncytial Viruses
Study type: Observational
Recruitment status: Active, not recruiting
Enrolment: 1 participants (actual)
Lead sponsor: PfizerIndustry (pharma, biotech, devices)
Study start: 24 Feb 2025 (actual)
Primary completion: 31 Jul 2027 (estimated)
Study completion: 31 Jul 2027 (estimated)
First posted: 7 Feb 2025 (actual)
Results: Not posted in the source record

Clinical summary

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

There will be no active enrollment of study participants, no direct contact with study participants, and no collection of any primary data outside of the Standard of Care (SOC).

Study design

Observational model: Case-control
Time perspective: Retrospective
Number of arms: 2

Arm	Type	Receives
Case	–	Biological: ABRYSVO VaccinationCases for the primary objective will be infants meeting the outcome definition who had any positive laboratory-confirmed RSV test from a respiratory sample collected within 10 days prior to hospital admission through 3 days after hospital admission.
Control	–	Biological: ABRYSVO VaccinationControls for the primary objective will be infants meeting the outcome definition who had a laboratory-confirmed negative RSV test from a respiratory sample collected within 10 days prior to hospital admission through 3 days after hospital admission.

Who may qualify

Ages: 0 to 6 months
Sex: All
Healthy volunteers: Not accepted
Age groups: Child
Study population: The study population will include infants who were hospitalized with ARI, have documented RSV test results and born to an individual eligible for ABRYSVO vaccination in pregnancy based on the timing of birth relative to the local seasonal ABRYSVO vaccination program.

Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.

Interventions

Intervention	Type	Arms
ABRYSVO VaccinationThe primary exposure of interest for the TND study is maternal history of vaccination with Pfizer's ABRYSVO vaccine during pregnancy with the infant who presented for care. Infants will be considered "exposed to ABRYSVO" if their birth parent has documented evidence of receiving ABRYSVO ≥14 days before the date of the infant's birth, during the licensed gestational age window of 32 0/7 to 36 6/7 weeks.	Biological	Case, Control

Primary outcome

RSV-positive ARI hospitalization confirmed by ³1 ARI symptom, laboratory testing, and hospitalization occurring 0 to ≤ 90 days of life during RSV season based on local epidemiology.
Time frame: 0 to ≤ 90 days of life

7 secondary outcomes

RSV-positive ARI hospitalization confirmed by ³1 ARI symptom, laboratory testing, and hospitalization occurring 0 to ≤ 180 days of life during RSV season based on local epidemiology.
Time frame: 0 to ≤180 days of life
RSV-positive ARI hospitalization confirmed by ≥ 1 ARI symptom, laboratory testing, and hospitalization occurring 91 to ≤180 days of life during the RSV season based on local epidemiology
Time frame: 91 to ≤180 days of life
RSV-positive ARI hospitalization with study-defined LRTD occurring 0 to ≤ 90 days of life during RSV season based on local epidemiology.
Time frame: 0 to ≤90 days of life
RSV-positive hospitalization with study-defined LRTD occurring 0 to ≤180 days of life during the RSV season based on local epidemiology.
Time frame: 0 to ≤180 days of life
RSV-positive ARI hospitalization with study-defined LRTD occurring 91 to ≤ 180 days of life during RSV season based on local epidemiology.
Time frame: 91 to ≤ 180 days of life
Number, age and characteristics of infants whose birth parent received ABRYSVO during pregnancy who present for a medical visit (outpatient, urgent care, emergency room, hospital) and have laboratory confirmed RSV between 0 to ≤ 90 days of life
Time frame: 0 to ≤90 days of life
Number, age and characteristics of infants who received Beyfortus or Enflonsia between 0 to <7 days of life who present for a medical visit and have laboratory confirmed RSV between 1 to ≤ 96 days post-B
Time frame: 1 to ≤96 days post-Beyfortus/Enflonsia exposure

Results and safety

This study is still under way. Results are not available in the source record yet.

Research links

Official record on ClinicalTrials.govLast updated by the sponsor 3 Feb 2026.
To obtain contact information for a study center near you, click here.Link provided by the sponsor.
Individual participant dataSharing planned: No. Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical_trials/trial_data_and_results/data_requests.

Related trials for Respiratory Syncytial Viruses

RecruitingPhase 3
Study to Learn About a Respiratory Syncytial Virus Vaccine in Children at High Risk of RSV Disease
Respiratory Syncytial Virus (RSV)
Active, not recruitingPhase 3
A Study on the Immune Response and Safety of Vaccine Against Respiratory Syncytial Virus Given to Chinese Adults 18 to 59 Years of Age at Increased Risk of Respiratory Syncytial Virus Disease
Respiratory Syncytial Virus Infections
Active, not recruitingPhase 1
A Phase 1 Study to Evaluate JCXH-108, an mRNA-based Vaccine Against RSV
Respiratory Syncytial Virus (RSV), Infectious Disease
RecruitingPhase 2
Immunogenicity of RSVPreF3 Vaccine in Immunocompromised Persons
Respiratory Syncytial Virus (RSV)
RecruitingObservational study
TARSILA Real-World Evidence Study
Respiratory Syncytial Virus (RSV), Maternal Immunization

Referral and contact

AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.

Pfizer CT.gov Call Center study director

Pfizer

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

Questions about this trial

What is this clinical trial studying?

An observational study of Respiratory Syncytial Viruses, run by Pfizer at 1 site in United States.

The full registered description is in the About this study section and the official record.

Who may be eligible to take part?

Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.

Is this clinical trial currently recruiting?

The record says: under way, not looking for participants, as of the sponsor's last update on 3 Feb 2026. Status can change between updates, so confirm with the study contact before making plans.

Where is the study taking place?

The record lists 1 site in United States. Whether a site is taking part right now should be confirmed with that site. See every site.

What are the possible benefits and risks?

They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.

Are results available for this study?

This study is still under way. Results are not available in the source record yet.

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

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

What does the primary outcome measure?

RSV-positive ARI hospitalization confirmed by ³1 ARI symptom, laboratory testing, and hospitalization occurring 0 to ≤ 90 days of life during RSV season based on local epidemiology. (time frame: 0 to ≤ 90 days of life). It is what the study was designed to measure, not a finding.

Where can I read the original study information?

On the ClinicalTrials.gov record for NCT06813872.

Does a listing mean the treatment is approved or proven to work?

No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.

How often is this information updated?

AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 3 Feb 2026.