Expert Q&A

Bivalent Prefusion F Vaccine For Older Adults

Older adults, particularly those that are aged 65 or older, are at the highest risk for severe respiratory syncytial virus (RSV). The FDA has approved several vaccines to help at-risk populations from RSV.

Consultant360 reached out to a spokesperson with Pfizer to learn more about the study that evaluated the use of the bivalent prefusion F vaccine to protect older adult patients from RSV.

Consultant360: Please explain how your study, “Efficacy and safety of a bivalent RSV prefusion F vaccine in older adults,”1 came about.

Pfizer Spokesperson: RSV disease is characterized by several respiratory symptoms varying from mild to more severe disease, with the more severe disease having more symptoms. An independent, external Data Monitoring Committee (DMC) conducted a pre-planned, interim analysis of Pfizer’s RSVpreF efficacy to assess protection against RSV-associated lower respiratory tract illness (LRTI-RSV), which is defined by two or more symptoms. The analysis demonstrated vaccine efficacy: 66.7% (96.66% CI: 28.8%, 85.8%). This positive result enabled Pfizer to look at the more severe disease primary endpoint of LRTI-RSV defined by three or more symptoms where vaccine efficacy of 85.7% (96.66% CI: 32.0%, 98.7%) was observed.

The DMC also indicated the investigational vaccine was well-tolerated, with no safety concerns. We received an approval from the FDA for the vaccine on Wednesday, May 31, 2023.

C360: How do your findings contribute to the existing literature on this topic?

Pfizer Spokesperson: We’ve published a Phase 2 study in the New England Journal of Medicine.2

C360: The FDA has approved some RSV vaccines for older adults. How does the prefusion F vaccine differ from the others?

Pfizer Spokesperson: Pfizer’s investigational RSV vaccine candidate builds on foundational basic science discoveries including those made at the National Institutes of Health (NIH), which detailed the crystal structure of prefusion F, a key form of the viral fusion protein (F) that RSV uses to enter human cells. The NIH research showed that antibodies specific to the prefusion form were highly effective at blocking virus infection, suggesting a prefusion F-based vaccine may confer optimal protection against RSV. After this important discovery, Pfizer tested numerous versions of a stabilized prefusion F protein and identified a candidate that elicited a strong anti-viral immune response in pre-clinical evaluations. The bivalent vaccine candidate is composed of equal amounts of recombinant RSV prefusion F from subgroups A and B.

C360: How do the results of your study impact clinical practice and the prevention of RSV in older adults?

Pfizer Spokesperson: This is an exciting time—not just for our team at Pfizer—but for the entire medical field. And it is, in fact, the very first time a vaccine has been convincingly shown to safely protect older adults from severe RSV-related lower respiratory tract illness. Researchers have spent decades working to develop a vaccine against RSV, with failed trials going back to the 1960s. This is a breakthrough the medical community has been eagerly awaiting.

C360: What are the next steps in research?

Pfizer Spokesperson: Our work does not stop here. We are studying the potential use of our vaccine in immunocompromised adults and will be reviewing our full second-season data in the coming weeks.



  1. Walsh EE, Marc GP, Zareba AM, et al. Efficacy and safety of a bivalent RSV prefusion F vaccine in older adults. N Engl J Med. 2023;388:1465-1477. doi:10.1056/NEJMoa2213836
  2. Simões EAF, Center KJ, Tita ATN, et al. Prefusion F Protein–Based Respiratory Syncytial Virus Immunization in Pregnancy. N Engl J Med. 2022;386:1615-1626. doi:10.1056/NEJMoa2106062

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