Loading ...

TOPLINE:

Maternal respiratory syncytial virus (RSV) prefusion F (RSVpreF) vaccination during pregnancy is associated with more than 65% protection against RSV-associated acute respiratory illness (ARI) hospitalization in infants 90 days or younger. Among 274 hospitalized infants, 11 of 83 with RSV and 71 of 191 control individuals were born to vaccinated individuals, with vaccine effectiveness estimated at 67.6% against ARI hospitalization and 69.0% against lower respiratory tract disease (LRTD) hospitalization.

METHODOLOGY:

• Researchers conducted a retrospective case-control study using a test-negative design within a single health system in western Pennsylvania during the 2023-2024 and 2024-2025 RSV seasons.
• A total of 274 infants 90 days or younger were included, born between October 1, 2023, and April 15, 2024, or between September 1, 2024, and April 30, 2025, who were hospitalized with ARI and tested for RSV.
• Maternal RSVpreF vaccination was defined as administration at gestational age between 32 weeks 0-7 days and 36 weeks 6-7 days and at least 14 days before delivery.
• Primary outcome was RSV-associated ARI requiring hospitalization, while the secondary outcome was RSV-associated LRTD requiring hospitalization in infants aged 0-90 days.
• Vaccine effectiveness was estimated as (1-adjusted odds ratio) × 100% comparing the odds of maternal RSVpreF vaccination among RSV-positive infants vs RSV-negative infants using multivariable logistic regression.

TAKEAWAY:

• Vaccine effectiveness against RSV-associated ARI hospitalization was estimated at 67.6% (95% CI, 33.2%-85.4%) for infants aged 0 through 90 days and 74.2% (95% CI, 25.4%-93.0%) for infants aged 0-30 days.
• Vaccine effectiveness against RSV-associated LRTD hospitalization was estimated at 69.0% (95% CI, 25.5%-88.0%) from 0 through 90 days of age.
• Among 83 case infants with RSV, 72 (86.7%) had LRTD, 28 (33.7%) required ICU admission, and 56 (67.5%) required supplemental oxygen or respiratory support; no deaths occurred.
• Sensitivity analysis including infants born to mothers who received the RSVpreF vaccine less than 14 days before delivery showed an estimated effectiveness of 64.3% (95% CI, 30.2%-82.6%).

IN PRACTICE:

“Maternal RSVpreF vaccination was associated with protection against RSV-associated ARI and LRTD hospitalization among infants 90 days or younger. These findings provide early clinical evidence supporting the effectiveness of maternal RSVpreF vaccination in preventing RSV-associated hospitalization in infants,” wrote the authors of the study.

SOURCE:

The study was led by Anne-Marie Rick, MD, MPH, PhD, University of Pittsburgh School of Medicine, Pittsburgh. It was published online on June 5 in JAMA Network Open.

LIMITATIONS:

As an observational study, residual confounding and possible vaccination misclassification cannot be fully excluded. Vaccination during pregnancy may reflect access to and use of healthcare services, with potential differences in care-seeking influencing outcome ascertainment. While the sample size was sufficient for the primary analysis, the number of vaccinated cases contributing to the primary outcome and to the subgroup estimates was small, which limits the precision of the vaccine effectiveness estimate and is reflected in the wide 95% CIs. The integrated health system mitigates incomplete capture, but residual bias may remain.

DISCLOSURES:

The study received support from Pfizer Inc. through a collaboration with the University of Pittsburgh. Rick disclosed receiving grant support from Pfizer Inc. during the conduct of the study and personal fees for serving as site principal investigator for a vaccine trial from Pfizer Inc. outside the submitted work. The study also received support from the Department of Biomedical Informatics through the National Institutes of Health and the Clinical and Translational Sciences Institute at the University of Pittsburgh. Additional disclosures are noted in the original article.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.