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Road to RSV Vaccines: Awaiting FDA Approval Following Phase 3 Trial Results

Respiratory syncytial virus, known as RSV, has been described by one prominent researcher as the “worst disease that no one knows about.” Each year, this respiratory virus infects millions of people and sends hundreds of thousands of them to the hospital. Unfortunately, this virus is responsible for thousands of deaths each year. The very young and very old are most susceptible to the virus due to their weaker immune systems. Furthermore, when the virus is circulating with other seasonal viruses, such as influenza and COVID-19, the sheer volume of infections can put a great strain on the healthcare system. 

Fortunately, several RSV vaccines are currently in development. Recently, the U.S. Food and Drug Administration (FDA) approved progression in Phase 3 of a clinical trial for one of these vaccines. Progress in a RSV vaccine trial represents a huge success from a population health standpoint. Here’s what you need to know about the RSV vaccine that is progressing in its Phase 3 clinical trial. 

What Progress Has Been Made on the RSV Vaccination Front? 

Scientists have been working on a successful RSV vaccine for decades. However, an RSV vaccine has yet to be approved. In February 2023, Pfizer presented its efficacy and safety data to the FDA to show how Phase 3 of its clinical vaccine trial is progressing. This Phase 3 study, known as the “efficacy study,” began in August 2021. It’s designed to measure the safety of the RSV vaccine, its immunogenicity (how significantly it triggers an immune response), and its efficacy (how well it works to achieve specific endpoints). The study is conducted in the U.S., Canada, the Netherlands, Finland, Argentina, Japan, and South Africa. One arm of the study is investigating the effects of a single dose of the RSV vaccine, and two sub-arms are investigating the effects of two doses spaced over one year and two years. 

What Does the Efficacy Data Show for the Pfizer RSV Vaccine? 

Compared to a placebo, a single dose of the Pfizer vaccine, currently known as the RSVpreF vaccine, was shown to prevent lower respiratory tract infections and illness caused by RSV in adults over 60. 

The Phase 3 trial data concluded the following: 

  • The vaccine prevented general illness with 66.7% efficacy 
  • The vaccine prevented lower respiratory tract infection with three or more symptoms with 85.7% efficacy 
  • The vaccine prevented acute respiratory infection with 62.1% efficacy 

Once this data was presented to the FDA’s vaccine advisory committee, known as the Vaccines and Related Biological Products Advisory Committee (VRBPAC), the committee ultimately voted in favor of recommending the vaccine for the FDA’s approval. 

When Will the RSV Vaccine Be Available? 

Now that Pfizer’s RSV vaccine has been recommended for approval following the data from Phase 3 of the clinical trial, the FDA must next approve the vaccine. According to certain experts, the FDA typically follows the recommendations of its VRBPAC committee. However, the FDA’s approval may take a few months. If the vaccine receives approval, Pfizer will be allowed to license and market the vaccine in the United States. Even after the vaccine becomes available, it will be continually monitored in an ongoing Phase 4 clinical trial. 

What Kind of Formulation Is Pfizer’s RSV Vaccine? 

Pfizer’s RSV vaccine is similar to other vaccines used for respiratory illnesses (such as the influenza shot) because it doesn’t contain live viruses. Instead, it contains the fusion protein that is characteristic of the RSV virus. This allows the body to recognize this protein and create immunologic cells targeting the protein. Therefore, when someone encounters the virus, their body is prepared to defend against it. This particular vaccine also has a “backup” mechanism, which is a piece of viral DNA that codes for the fusion protein. That way, a vaccinated person’s immune system can target both the fusion protein itself, as well as its instruction manual. 

How to Learn More About the Pfizer RSV Vaccine Trial 

To see the most up-to-date information about the RSV vaccine trial, visit the trial’s entry on ClinicalTrials.gov. 

Research and materials for this article were compiled, written, and distributed on behalf of the National Public Health Information Coalition. The views and opinions expressed in this blog are those of the various authors and do not necessarily reflect the official policy or position of the National Public Health Information Coalition or its members. 


[1] Race to RSV vaccine approval: URMC Researchers Leading the Way. https://www.urmc.rochester.edu/news/story/race-to-rsv-vaccine-approval-urmc-researchers-leading-the-way 

[2] Epidemiology and Burden of Respiratory Syncytial Virus in Older Adults in the U.S. 


[3] Study to Evaluate the Efficacy, Immunogenicity, and Safety of RSVpreF in Adults. https://clinicaltrials.gov/ct2/show/NCT05035212 

[4] Efficacy and Safety of a Bivalent RSV Prefusion F Vaccine in Older Adults. https://www.nejm.org/doi/full/10.1056/NEJMoa2213836 

[5] FDA advisers vote in favor of approval for RSV vaccines for older adults. https://www.cnn.com/2023/02/28/health/fda-rsv-vaccine/index.html 

[6] Vaccine development 101. https://www.fda.gov/vaccines-blood-biologics/development-approval-process-cber/vaccine-development-101 



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