Pfizer’s respiratory syncytial virus (RSV) pipeline appears to have run dry of candidates following the cessation of work on both an oral medicine and an RSV-flu combo vaccine in quick succession.
An updated pipeline list published along with the company’s third-quarter earnings release this morning shows that the Big Pharma has halted work on PF-07941314, an early-stage RSV and flu combo vaccine. The prophylactic vaccine consists of a protein subunit and mRNA component and had been in phase 1 development.
It follows Pfizer’s decision earlier this month to pause work on sisunatovir, an oral inhibitor designed to treat RSV in both kids and adults. Clinical development of sisunatovir faced “ongoing challenges,” including a drug-drug interaction with antacids, a spokesperson told Fierce Biotech at the time. The candidate was acquired as part of Pfizer’s $525 million buyout of ReViral in 2022.
Earlier this month, a company spokesperson said Pfizer would “focus our efforts on identifying and advancing the development of other investigational therapeutics that have the greatest potential to prevent and treat RSV disease and other viral respiratory pathogens.”
However, Pfizer’s pipeline doesn’t list any other RSV candidates beyond the recently halted sisunatovir. Fierce now understands that Pfizer is considering some formulation changes to sisunatovir and could yet restart the program. The company is also not ruling out the development of other earlier-stage RSV treatments if they offer an opportunity to address unmet medical needs.
A spokesperson this morning pointed to the ongoing launch of Abrysvo, which gained FDA approval in May of 2023 to vaccinate older adults against lower respiratory tract disease (LRTD) caused by RSV. A few months later, the FDA approved the shot for pregnant people to vaccinate their babies against RSV.
That shot—which brought in $356 million in third-quarter revenue—is locked in a competition with GSK’s Arexvy and Moderna’s mRESVIA.
Pfizer's RSV rollback comes as the space has grown increasingly crowded. Besides marketed vaccines, Sanofi and AstraZeneca sell an antibody to protect infants, with Merck & Co. now eying a piece of that market with its own late-stage candidate.
Pfizer's pipeline update this morning also showed that another phase 1 trial has been halted for the CDK2 inhibitor PF-07104091, this time in ovarian cancer. However, work to test the small molecule in breast cancer as both a monotherapy and in combination with the CDK4 inhibitor atirmociclib continues.
Atirmociclib saw one of its own trials halted in the form of a study testing the candidate in combination with Xtandi for prostate cancer, according to the update.