Pfizer Shares Positive Phase III Data for Maternal RSV Vaccine Candidate

Pfizer announced positive top-line data from a Phase III trial evaluating its respiratory syncytial virus (RSV) prefusion vaccine candidate, RSVpreF (or PF-06928316) for pregnant individuals to help protect their infants from RSV disease after birth.

RSV is a respiratory virus that causes common cold-like symptoms but can lead to severe and life-threatening lower respiratory tract infections (LRTIs) like pneumonia in high-risk populations such as young infants, older adults and immunocompromised individuals.

Results of the Phase III MATISSE (MATernal Immunization Study for Safety and Efficacy) trial, which involved approximately 7,400 pregnant individuals, showed that administration of the bivalent candidate RSV vaccine during pregnancy led to a significant reduction in the rate of severe medically attended lower respiratory tract illness (MA-LRTI) in newborns.

The efficacy against severe MA-LRTI was 81.8 percent through the first 90 days of life and went down to 69.4 percent over the six-month follow-up period in the interim efficacy analysis conducted by an external and independent Data Monitoring Committee (DMC).

The results met one of two primary endpoints. The second primary endpoint was not met because although a clinically meaningful efficacy of 57.1 percent was observed for MA-LRTI in the first 90 days of life, it fell to a statistically insignificant low of 51.3 percent over the six-month follow up period.

However, the results for the first primary endpoint were strong enough that it prompted the study DMC to recommend that the company move ahead and file with the US Food and Drug Administration (FDA). The committee said the candidate vaccine provides safe and effective protection against RSV, especially during the winter season.

Related: Pfizer to Acquire RSV Antiviral Developer ReViral in $525 Million Deal

Pfizer CEO Albert Bourla noted that more than an estimated 177,000 older adults are hospitalized from RSV in the US each year, and 14,000 of them die from it.

In the announcement, Pfizer said it plans to submit a Biologics License Application (BLA) to the FDA by the end of this year for the vaccine candidate and other regulatory authorities thereafter in the coming months.

There is currently no treatment or vaccine for the prevention of RSV in newborns so Pfizer’s shot would be the first. The vaccine will instead be going up against long-acting antibodies being developed by AstraZeneca and Sanofi for administration in infants. In a Phase III clinical trial, the two pharma giants revealed one of the candidate antibodies, nirsevimab, led to 74.5 percent efficacy against medically attended RSV-associated lower respiratory tract infection.

Pfizer’s RSV vaccine candidate received Breakthrough Therapy Designation from the FDA on March 2, 2022 for the prevention of RSV-associated lower respiratory tract disease in infants up to six months of age by active immunization of pregnant women. The FDA designation was based on the results of the Phase IIb proof-of-concept study of RSVpreF, which evaluated the safety, tolerability and immunogenicity of the vaccine in pregnant women ages 18 through 49 and their infants.

Pfizer has been bolstering its RSV portfolio and as part of that, completed the acquisition of RSV therapeutics biotech ReViral in a deal worth $525 million in June of this year. The transaction included therapeutic candidates such as sisunatovir, which is currently in Phase II clinical development in infants.