Impact and Effectiveness of ABRYSVO® Vaccination During Pregnancy (BERNI)

Real World Impact and Effectiveness of ABRYSVO® Vaccination During Pregnancy Against RSV Illness in Infants

This study will be conducted in collaboration with a research network of independent hospital sites to evaluate the vaccine effectiveness (VE) and impact of ABRYSVO vaccination during pregnancy in a real-world population over multiple seasons, which began in 2024 across Argentina and beginning in 2025 in Uruguay. We will use three retrospective design approaches in this study:

(i) a test negative design (TND) to evaluate real-world VE of maternal ABRYSVO against RSV-associated outcomes in infants;

(ii) a descriptive cohort design to evaluate the clinical evolution of infants hospitalized with RSV-positive lower respiratory tract disease (LRTD); and

(iii) an ecologic before-and-after design to evaluate the impact of ABRYSVO vaccination during pregnancy on infant RSV-associated and all-cause respiratory outcomes.

Study Overview

• Status: Active, not recruiting
• Conditions: Respiratory Tract Diseases; Respiratory Syncytial Virus
• Intervention / Treatment: Biological: ABRYSVO

Detailed Description

This hospital-based retrospective study will be conducted in a research network of independent hospital sites. We will collect data from hospital medical records, supplemented with information from vaccine registries. This study will use three retrospective design approaches: a test negative design (TND) to evaluate real-world vaccine effectiveness (VE) of maternal ABRYSVO against RSV-associated LRTD hospitalization and other outcomes in infants, a descriptive cohort design to evaluate the clinical features of infants hospitalized with RSV-positive LRTD, and an ecologic before-and-after design to evaluate the impact of ABRYSVO vaccination during pregnancy on infant RSV-associated and all-cause respiratory outcomes.

The TND study will include infants through 9 months of age who were admitted to one of the participating hospital sites with symptoms of respiratory infection, born at 32 weeks of gestational age or greater, met the definition of LRTD, had a respiratory specimen collected with an RSV test result through standard of care testing, born 14 days or more after start of the first seasonal ABRYSVO vaccination campaign, and born to individuals who were expected to reach the indicated ABRYSVO vaccination window during a local ABRYSVO vaccination season. To complement the VE estimates generated in the TND study, we will use the cases from the primary objective of the TND analysis as a cohort of participants to describe the endpoints in the descriptive cohort study. The ecologic before-and-after study will include information for infants and children ≤24 months of age meeting eligibility criteria in post-ABRYSVO program implementation years and in several historical RSV seasons pre-ABRYSVO program implementation.

For the TND study, a multivariable logistic regression model, adjusted for confounding, will be used to compute an adjusted odds ratio (aOR), comparing the odds of maternal ABRYSVO vaccination during pregnancy between test-positive cases and test-negative controls. VE will be estimated as (1-aOR) x 100%. Secondary and exploratory objectives will evaluate VE estimates stratified by several characteristics. For the descriptive cohort study of RSV-positive LRTD hospitalized infants ≤9 months of age (i.e., the cases from the primary objective of the TND study), infant characteristics, timing, severity/clinical features, and use of healthcare resources during the index hospitalization will be described. For the ecologic before-and-after study, the impact of maternal ABRYSVO introduction on rates of RSV-associated and all-cause outcomes among infants ≤6 months (compared with older age groups) over multiple RSV seasons will be described overall and by epidemiological week, calendar year, calendar month, age group, and hospital site. These analyses will begin in the 2024 RSV season in Argentina and continue in future RSV seasons in Argentina and Uruguay (2025 and 2026), with comparison to several pre-ABRYSVO implementation seasons. Quasi-experimental approaches will also be used to quantitatively compare incidence of study outcomes among infants aged ≤6 months with older age groups.

• Study Type: Observational
• Enrollment (Actual): 1

Contacts and Locations

Study Locations

• Argentina
  • Buenos Aires, Argentina
    • Pfizer

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Child
• Accepts Healthy Volunteers: No

• Sampling Method: Probability Sample

Study Population

Test Negative Design: All infants through 9 months of age who were admitted to one of the participating hospital sites with symptoms of respiratory infection, born at 32 weeks of gestational age or greater, met the definition of LRTD, had a respiratory specimen collected with an RSV test result through standard of care testing, born 14 days or more after start of the first seasonal ABRYSVO vaccination campaign, and born to individuals who were expected to reach the indicated ABRYSVO vaccination window during a local ABRYSVO vaccination season.

Cohort Design: RSV positive cases from the TND study.

Ecologic Before-and-After Design: All infants and children ≤24 months of age admitted to one of the participating hospital sites and meeting eligibility criteria.

Description

Test Negative Design Inclusion Criteria:

1. Infants ≤9 months (≤270 days) of age on the index date.
2. Index date within the time period for data collection (approximately 01 April to 30 September in 2024, 2025, or 2026).
3. Infants born at 32 weeks of gestational age or greater.
4. Hospitalized for at least 24 hours with LRTD (symptoms related to LRTD might be absent at the time of admission but if they develop within the first 24 hours of hospitalization, the criteria for LTRD will be considered met), and specimen collected for RSV within 10 days prior to hospital admission through 3 days after a hospital admission through SOC testing.
5. Infant date of birth 14 days or more after start of the first seasonal ABRYSVO vaccination campaign, to ensure potential to have been born to an ABRYSVO-vaccinated individual.
6. Infant 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 a local ABRYSVO vaccination season.

Test Negative Design Exclusion Criteria:

1. Received any licensed or investigational RSV preventive product (e.g., Palivizumab, Nirsevimab, active RSV vaccine) since birth.
2. Received ≥1 blood transfusion or other blood products containing antibody (e.g., fresh frozen plasma) since birth.
3. Born to individual who received any other licensed or investigational RSV vaccine during pregnancy.
4. Born to individual for whom ABRYSVO vaccination status cannot be confirmed in available data sources.
5. Infants with LRTD that require hospitalization for reasons other than clinical criteria (e.g., for social reasons, other medical condition in an infant with LRTD without hospitalization criteria).

Cohort Design Inclusion Criteria:

1. RSV positive cases ≤9 months of age from the TND study.

Cohort Design Exclusion Criteria: None.

Ecologic Before-and-After Design Inclusion Criteria:

1. Infants and children ≤24 months of age on the index date.
2. Index date during the calendar years for data collection (pre- or post-ABRYSVO program implementation.
3. Meets ≥1 outcome definition during the time period for data collection.

Ecologic Before-and-After Design Exclusion Criteria: None.

Study Plan

How is the study designed?

Number of groups / cohorts

3

Cohorts and Interventions

Group / Cohort	Intervention / Treatment
Cases (Test Negative Design and Cohort Design); Infants who meet the respiratory case definition and test positive for RSV (result obtained from standard of care (SOC) testing).	Biological: ABRYSVO; Test Negative Design: This is a non-interventional retrospective study; therefore, ABSYRVO vaccine has already been administered according to the standard of care. ABRYSVO is a bivalent RSV prefusion F protein-based vaccine (RSVpreF) composed of two prefusion F proteins to protect against both RSV-A and RSV-B. Ecologic Before-and-After Design: This is an ecologic before-and-after study using aggregated data; as such, the 'exposure' of interest is time before ABRYSVO program implementation (i.e., five historical pre-ABRYSVO RSV seasons) and time after ABRYSVO implementation (i.e., post-ABRYSVO RSV seasons: 2024-2026).
Controls (Test Negative Design); Infants who meet the respiratory case definition and test negative for RSV (result obtained from standard of care (SOC) testing).	Biological: ABRYSVO; Test Negative Design: This is a non-interventional retrospective study; therefore, ABSYRVO vaccine has already been administered according to the standard of care. ABRYSVO is a bivalent RSV prefusion F protein-based vaccine (RSVpreF) composed of two prefusion F proteins to protect against both RSV-A and RSV-B. Ecologic Before-and-After Design: This is an ecologic before-and-after study using aggregated data; as such, the 'exposure' of interest is time before ABRYSVO program implementation (i.e., five historical pre-ABRYSVO RSV seasons) and time after ABRYSVO implementation (i.e., post-ABRYSVO RSV seasons: 2024-2026).
Ecologic Cohort (Ecologic Before-and-After Design); Aggregated data on study outcomes from five historical RSV seasons and from 2024-2026 RSV seasons (data during the COVID-19 pandemic are excluded).	Biological: ABRYSVO; Test Negative Design: This is a non-interventional retrospective study; therefore, ABSYRVO vaccine has already been administered according to the standard of care. ABRYSVO is a bivalent RSV prefusion F protein-based vaccine (RSVpreF) composed of two prefusion F proteins to protect against both RSV-A and RSV-B. Ecologic Before-and-After Design: This is an ecologic before-and-after study using aggregated data; as such, the 'exposure' of interest is time before ABRYSVO program implementation (i.e., five historical pre-ABRYSVO RSV seasons) and time after ABRYSVO implementation (i.e., post-ABRYSVO RSV seasons: 2024-2026).

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
RSV-associated LRTD hospitalization among infants	Lab-confirmed RSV-positive LRTD hospitalization occurring ≤180 days after birth	From birth through 6 months of age

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
RSV-associated severe LRTD hospitalization among infants	Lab-confirmed RSV-positive severe LRTD hospitalization occurring ≤180 days after birth	From birth through 6 months of age
RSV-associated LRTD hospitalization among infants, stratified by temporal and clinical characteristics	Lab-confirmed RSV-positive LRTD hospitalization occurring ≤180 days after birth	From birth through 6 months of age

Collaborators and Investigators

• Sponsor: Pfizer
• Collaborators: iTrials S.A.
• Investigators: Study Director: Pfizer CT.gov Call Center, Pfizer

Publications and helpful links

Helpful Links

• To obtain contact information for a study center near you, click here.

Study record dates

Study Major Dates

• Study Start (Actual): August 26, 2024
• Primary Completion (Estimated): October 1, 2026
• Study Completion (Estimated): October 15, 2026

Study Registration Dates

• First Submitted: October 16, 2024
• First Submitted That Met QC Criteria: October 16, 2024
• First Posted (Actual): October 18, 2024

Study Record Updates

• Last Update Posted (Actual): May 15, 2026
• Last Update Submitted That Met QC Criteria: May 12, 2026
• Last Verified: May 1, 2026

More Information

Terms related to this study

• Keywords: Pregnancy; Vaccine; Cohort; Hospitalized; Effectiveness; Infants; Maternal; Immunization; Hospitalization; Retrospective; Respiratory Syncytial Virus; Respiratory outcomes; Lower respiratory tract disease; Case control; ABRYSVO; Test Negative Design; Ecologic; Prefusion F protein-based
• Additional Relevant MeSH Terms: Respiratory Tract Diseases; abrysvo
• Other Study ID Numbers: C3671068; NCT06647654 (Registry Identifier: ClinicalTrials.gov)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: 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.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: Yes
• Studies a U.S. FDA-regulated device product: No
• product manufactured in and exported from the U.S.: No