Positive Results for RSV Vaccine in Substudy of Phase III Trial of Immunocompromised Patients

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Pfizer’s Abrysvo, currently the only approved vaccine for respiratory syncytial virus (RSV) in both older adults and infants through maternal immunization, yielded positive top-line safety and immunogenicity results in a substudy of an ongoing Phase III clinical trial (MONeT, or RSV Immunization Study for Adults at Higher Risk of Severe Illness), Pfizer announced in a press release on Aug. 12, 2024 (1,2). Two doses of Abrysvo were given to immunocompromised individuals age 18 and older who are at risk of developing severe RSV-associated lower respiratory tract disease (LRTD).

“Immunocompromised adults, such as patients with cancer or autoimmune disorders, have a substantially increased risk of experiencing severe complications from RSV, yet there are currently no vaccines approved for those aged 18 to 59 in the [United States],” said Annaliesa Anderson, Pfizer senior vice president and chief scientific officer for vaccine research and development. “We are encouraged by the positive top-line data from this study, which provide important evidence that Abrysvo has the potential to address a significant unmet need in this vulnerable population.”

As Pfizer said in the press release, RSV—which is responsible for up to 160,000 hospitalizations and 13,000 deaths each year in the US alone—is contagious and a common cause of respiratory illness (1). It can impact the lungs and breathing passages of those affected, raising particular risk to certain younger and older age groups as well as people with some chronic medical conditions.

Abrysvo was approved by FDA for the prevention of LRTD caused by RSV in those 60 and older in May 2023, in infants from birth to six months by immunization of pregnant women at 32 to 36 weeks’ gestational age in August 2023 (both of those followed by approval actions from the European Commission, also in August 2023), was recommended as a maternal immunization by the US Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices in September 2023, and approved by Health Canada for both older adults and expectant mothers in January 2024 (3–7).

Prior clinical trial data of Abrysvo versus placebo suggested higher rates of low birth weight (5.1–4.4%) and jaundice (7.2–6.7%) in infants whose mothers had been given the vaccine at the targeted gestational age (1). Most common side effects in adults included fatigue, headache, nausea, muscle pain, and pain at the injection site.

References

1. Pfizer. Pfizer Announces Top-Line Results of Abrysvo for RSV in Immunocompromised Adults. Press Release. Aug. 12, 2024.
2. National Library of Medicine. A Study to Assess the Safety, Tolerability, and Immunogenicity of RSVpreF in Adults at High Risk of Severe RSV Disease (MONET). ClinicalTrials.gov, April 9, 2024 (accessed Aug. 12, 2024).
3. Pfizer. US FDA Approves Abrysvo, Pfizer’s Vaccine for the Prevention of Respiratory Syncytial Virus (RSV) in Older Adults. Press Release. May 31, 2023.
4. Pfizer. US FDA Approves Abrysvo, Pfizer’s Vaccine for the Prevention of Respiratory Syncytial Virus (RSV) in Infants Through Active Immunization of Pregnant Individuals 32-36 Weeks of Gestational Age. Press Release. Aug. 21, 2023.
5. Pfizer. European Commission Approves Pfizer’s Abrysvo to Help Protect Infants through Maternal Immunization and Older Adults from RSV. Press Release. Aug. 24, 2023.
6. Pfizer. Pfizer Broadens Portfolio of Respiratory Vaccines Recommended by CDC Advisory Committee with Abrysvo for RSV. Press Release. Sept. 22, 2023.
7. Pfizer Canada. Health Canada Approves Pfizer's Bivalent Respiratory Syncytial Virus (RSV) Vaccine for Older Adults and Infants Through Maternal Immunization. Press Release. Jan. 4, 2024.