Pfizer's Abrysvo Study: Assessing Safety in Pregnant Women and Infants

Pfizer Inc's ongoing clinical study, 'Special Investigation for ABRYSVO Intramuscular Injection – Investigation in Pregnant Women and Infants,' aims to assess the safety of the RSVpreF vaccine (Abrysvo) in pregnant women and their infants in Japan. The study is observational and follows a cohort model, with a prospective time perspective. The study began on October 1, 2024, and its primary completion and estimated completion dates are yet to be announced. The update could positively impact Pfizer's stock performance by reinforcing investor confidence in the company's vaccine portfolio.

Pfizer Inc.'s ongoing clinical study, 'Special Investigation for ABRYSVO Intramuscular Injection – Investigation in Pregnant Women and Infants,' aims to assess the safety of the RSVpreF vaccine (Abrysvo) in pregnant women and their infants in Japan. The study is observational and follows a cohort model, with a prospective time perspective. The study began on October 1, 2024, and its primary completion and estimated completion dates are yet to be announced. The update could positively impact Pfizer's stock performance by reinforcing investor confidence in the company's vaccine portfolio.

The study is part of a broader effort to combat Respiratory Syncytial Virus (RSV) infections, which are a significant cause of lower respiratory tract infections (LRTI) in infants under 6 months of age, premature infants, and those with chronic lung disease or congenital heart disease (CHD). According to a recent review [1], RSV is responsible for approximately 3.6 million hospital admissions and over 26,000 deaths among children under 5 years of age worldwide annually.

The RSVpreF vaccine, administered during pregnancy (gestational age 24–36 weeks), has shown promising results in reducing medically attended severe RSV-associated LRTI in infants. Maternal immunization with RSVPreF has demonstrated an efficacy of 81.8% at 90 days and 69.4% at 180 days after birth, respectively [1]. Additionally, long-acting RSV monoclonal antibodies like Nirsevimab have been found to provide season-long protection with a single dose for infants during their first RSV season, reducing both medically attended RSV-LRTI and hospitalizations by approximately 70%–80% [1].

The Strategic Advisory Group of Experts (SAGE) on immunization has recommended that countries consider implementing maternal RSVPreF vaccination and/or RSV monoclonal antibodies for infant RSV prevention [1]. Many countries have already adopted these interventions, demonstrating their cost-effectiveness. In 2024, the SAGE recommended the introduction of these interventions, which could further enhance Pfizer's market position in the RSV vaccine segment.

The clinical study in Japan, if successful, could provide additional data supporting the safety and efficacy of the RSVpreF vaccine, potentially leading to regulatory approvals and wider market adoption. This could translate into increased sales and revenue for Pfizer, positively impacting its stock performance. Investors may view the study as a significant milestone in Pfizer's vaccine portfolio, potentially boosting confidence in the company's ability to deliver innovative and effective healthcare solutions.

However, it is essential to note that the stock market's response to the study's results will depend on various factors, including the study's outcomes, regulatory approval timelines, and market competition. Additionally, the study's findings will be subject to peer review and scrutiny, which could impact its credibility and acceptance.

In conclusion, Pfizer's ongoing clinical study of the RSVpreF vaccine in Japan holds significant potential to reinforce investor confidence in the company's vaccine portfolio and positively impact its stock performance. The study's success could lead to regulatory approvals, increased market adoption, and enhanced revenue growth for Pfizer.

References:
[1] Napaporn Chantasrisawad et al. (2025). Beyond the first breath: comprehensive respiratory syncytial virus prevention through maternal immunization and infant immunoprophylaxis. Asian Biomed (Res Rev News) 19(3):116–130. https://www.researchgate.net/publication/394077372_Beyond_the_first_breath_comprehensive_respiratory_syncytial_virus_prevention_through_maternal_immunization_and_infant_immunoprophylaxis