How safe is Pfizer’s respiratory syncytial virus known as RSVpreF or Abrysvo? Abdallah Alami, MSc, BSc, University of Ottaway (School of Epidemiology and Public Health, Faculty of Medicine), and colleagues designed a case series study adverse event (AE) reports submitted to the U.S. Food and Drug Administration’s Vaccine Adverse Event Reporting System (VAERS) database following RSVPreF immunization from September 1, 2023, to February 23, 2024. Uploaded to the preprint server medRxiv, the surveillance data included all AE reports submitted to VAERS for pregnant individuals following vaccination. Using descriptive statistics to assess all AE reports with RSVPreF, including frequency, gestational age at vaccination, time to AE onset, and serious report proportions. The researchers utilized the Bayesian Confidence Propagation Neural Network (BCPNN), estimating the information component (IC) to identify disproportionate reporting of RSVPreF–event pairs.

It's important to note that this study outcome has not yet been peer-reviewed and published. Ideally, this finding gets vetted by peers for a comprehensive understanding of the output.

The Product

Pfizer’s RSVpreF (Abrysvo) was approved by the FDA in May 2023 for persons 60 years and above and by August 2023 for pregnant persons for two different uses:

Pregnant people

The only vaccine approved to protect infants from respiratory syncytial virus (RSV)-associated lower respiratory tract infection (LRTI) during pregnancy. It should be given as a single injection into the muscle between 32 and 36 weeks of pregnancy to protect infants from birth to 6 months of age. Common side effects in pregnant people include pain at the injection site, headache, muscle pain, and nausea.

Adults 60 and older

To prevent RSV-associated LRTD, The CDC's Advisory Committee on Immunization Practices (ACIP) officially recommended the vaccine for this use in June 2023. Common side effects in adults include fatigue, headache, pain at the injection site, and muscle pain.

Findings

The authors, report in VAERS 77 uploaded reports pertained to RSVPreF vaccination in pregnant individuals, with 42 (54.55%) classified as serious. The most reported non-pregnancy-specific AEs were headache, injection site erythema, and injection site pain.

Preterm birth was the most frequently reported pregnancy-specific AE, followed by preterm premature rupture of membranes, cesarean section, cervical dilatation, and hemorrhage during pregnancy.

The authors report in medRxiv that the median time from immunization to reported preterm birth was 3 days, with two-thirds of cases within a week.

Disproportionality analysis, a statistical method that compares the observed proportion of an adverse event for a specific drug to its expected proportion in a given set of data, is used to identify signals of disproportionate reporting (SDR) in adverse drug reactions (ADRs) spontaneous reporting (SR) databases. Disproportionality analysis is employed to identify whether SDR leads to regulatory action. This study pointed to a significant signal for various AEs, particularly highlighting preterm birth with an information component of 2.18 (95%CI, 1.54-2.63). This suggests that reports of preterm birth associated with RSVPreF vaccination occurred more frequently than statistically expected, and thus a concern. This is especially the case given the vulnerable nature of the cohort.

While the authors recognize that the “reported AEs were generally consistent with the safety profile observed in prelicensure studies, this study highlights ongoing concern about preterm birth among pregnant individuals following RSVPreF vaccination. Comprehensive longitudinal follow-up, including prospective pregnancy registries and infant follow-up studies, is urgently required.”

Lead Research/Investigator

Abdallah Alami, MSc, BSc, University of Ottaway (School of Epidemiology and Public Health, Faculty of Medicine); Corresponding Author
Santiago Perez-Lloret, MD, PhD, Consejo Nacional Investigaciones Cientificas y Tecnicas (CONICET), Buenos Aires
Donald R. Mattison, MD, MS, School of Epidemiology and Public Health, Faculty of Medicine, University of Ottawa; Risk Sciences International
https://www.trialsitenews.com/a/pfizer-rsv-vaccine-linked-to-adverse-eventspre-term-birth-safety-signal-in-pregnant-womenurgent-follow-up-recommended-966c9d64