2022-08-26| Trials & Approvals

Pfizer’s Bivalent RSV Candidate Demonstrates 85% Efficacy in Phase 3 Trials

by Reed Slater
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As the race between GSK, Janssen, Moderna, and Pfizer to develop an effective respiratory syncytial virus (RSV) vaccine comes closer to the finish line, Pfizer’s bivalent candidate, RSVpreF, demonstrated 85% efficacy in older adults in the Phase 3 RENOIR trials. Based on these results, Pfizer plans to submit a Biologics License Application (BLA) to the FDA in the coming months. 

Promising Results Among the Competition

Pfizer is up against GSK, Janssen, and Moderna, all of which have RSV vaccine candidates in Phase 3 trials. The rush to provide an RSV vaccine has hastened since the COVID-19 pandemic because now researchers have a better understanding of the cause of RSV and how to design a therapy to address the disease. 

RSV is a respiratory virus, most commonly resulting in serious conditions in infants and older adults. The disease can progress into bronchitis or even pneumonia in immunocompromised individuals. Infections result in approximately 117,000 hospitalizations in older adults each year and about 14,000 deaths. 

Early attempts to develop vaccines began in the 1960s but were unsuccessful, with one clinical trial even resulting in patient deaths. RSV stems from the prefusion F (preF) protein’s ability to sneak into human membrane cells and fuse with them. Researchers have understood that the F protein played a role in RSV for decades, but many focused on the postfusion stage. Now, researchers understand the need to target the preF protein before it experiences postfusion, resulting in RSV. 

Pfizer’s bivalent vaccine does just that, targeting two preF proteins to enhance protection against RSV A and B strains. The most recent clinical success of RSVpreF is keeping Pfizer in pace with its competitors as it hopes to make it to market soon.

Related Article: Moderna Follows Pfizer With Their Own Omicron BA.4/BA.5 Application to the FDA

Banking on Phase 3 RENOIR Clinical Trial Data

Pfizer’s most recent promising data comes from the (RSV vaccine Efficacy study iNOlder adults Immunized against RSV disease) RENOIR Phase 3 clinical trial. The Phase 3 leg consists of over 32,000 participants, creating a total of more than 37,000 participants throughout all phases of the RENOIR trials.

An independent Data Monitoring Committee found that the vaccine protected against RSV-associated lower respiratory tract illness (LRTI) with two or more symptoms with a 66.7% efficacy rate. Based on that positive result, Pfizer looked at the more severe disease primary endpoint with three or more symptoms of RSV-LRTI and found the vaccine demonstrated an 85.7% efficacy rate. 

Other companies are close on Pfizer’s heels, though. GSK’s RSV vaccine candidate is in Phase 3 trials, although it recently announced it would stop enrollment in trials including pregnant participants. AstraZeneca also has an RSV therapy in the works in the form of an investigational antibody, nirsevimab, which it is developing alongside Sanofi. The companies recently announced that Phase 3 and 2b data demonstrated the efficacy of 79.5% against RSV-LRTI. 

The most recent results from Pfizer’s bivalent RSV vaccine candidate are optimistic as the company eyes the first regulatory approval among its competitors. The competition is tight, though, and GSK, Janssen, and Moderna are keeping pace. The next few months will shed light on which company submits a BLA first and which vaccine candidate will make it to market the fastest, providing the first effective RSV vaccine in history. 

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