RESPIRATORY SYNCYTIAL VIRUS, SUBGROUP A, STABILIZED PREFUSION F PROTEIN 847A

Table of contents

• What is Respiratory Syncytial Virus?
• How does the RSV vaccine work?
• Which conditions is it used or studied for?
• How is the RSV vaccine given?
• What do the clinical trials show?
• Who can take part in these trials?
• What are the trials measuring?

What is respiratory syncytial virus?

Respiratory Syncytial Virus, subgroup A, stabilized prefusion F protein 847A is part of the active substance in Abrysvo, a bivalent recombinant vaccine against respiratory syncytial virus (RSV). The full active substance also includes the stabilized prefusion F protein from RSV subgroup B. Abrysvo is authorised as a medicine in the European Union, with Pfizer Europe MA EEIG as the authorisation holder.^[8] The product is given as a powder and solvent for solution for injection.

How does the RSV vaccine work?

Abrysvo contains stabilised versions of the prefusion F protein, a protein on the surface of RSV that the virus uses to enter human cells. Presenting this protein in its prefusion shape teaches the immune system to recognise RSV and produce antibodies against it. The vaccine is bivalent, meaning it targets both RSV subgroups A and B, and recombinant, meaning the proteins are produced in the laboratory rather than taken from the virus itself.

Which conditions is it used or studied for?

• Respiratory syncytial virus (RSV) infection — a common respiratory virus that can cause bronchiolitis and pneumonia, especially in infants and older adults.
• Bronchiolitis — inflammation of the small airways in the lungs, a frequent complication of RSV in babies.
• Respiratory tract infection — infections of the airways, ranging from mild cold-like illness to severe lung disease.
• Inflammatory rheumatic disease — conditions such as rheumatoid arthritis, where the immune system attacks the joints and other tissues.
• Allogeneic haematopoietic stem cell transplant recipients — people who have received blood-forming stem cells from a donor, leaving them immunocompromised.
• Lung transplant recipients — people who have received a donor lung and take immunosuppressive medicines.
• Prevention of lower respiratory tract disease caused by RSV — protecting children at high risk from serious RSV lung infections.

How is the RSV vaccine given?

Abrysvo is given as an intramuscular injection of 0.5 ml, prepared from a powder and solvent. In the trials, the dose is reported as 120 micrograms in some records and as 0.5 ml in others.^[4] The comparator vaccines Arexvy (also an RSV vaccine) and Beyfortus (an RSV antibody for infants) are given the same way.

What do the clinical trials show?

The eight trials in this record are all authorised and cover a wide range of populations. Seven are Phase 3 trials, one is Phase 2, and one is Phase 4. The largest is DAN-RSV, a pragmatic randomised trial in 690,000 adults aged 18 and older evaluating whether Abrysvo prevents hospitalisation for RSV-related respiratory disease.^[2] The smallest is a trial in 180 people with inflammatory rheumatic disease measuring antibody responses after one dose.^[3]

Two trials focus on infants. PIPELINE-RSV and its French sub-study test whether vaccinating the mother during pregnancy plus giving the infant antibody nirsevimab at 4 months protects better than either strategy alone.^[8][4] A separate Phase 3 study is testing Abrysvo in 920 children aged 5 to 18 years with chronic medical or immunocompromising conditions.^[6]

Three trials enrol transplant recipients. The RSV-Allo study is a Phase 4 trial in 204 allogeneic stem cell transplant recipients comparing Abrysvo and Arexvy.^[1] RSVaxID is a Phase 2 trial in 400 lung and stem cell transplant recipients.^[5] A revaccination study, DAN-RSV IC Revax, plans 29,000 immunocompromised adults to test a second dose of Abrysvo.^[7]

Who can take part in these trials?

• Pregnant women between 32 and 36 weeks of gestation, in the maternal vaccination trials.^[4]
• Infants up to 12 months of age, whose mothers were vaccinated or who receive the antibody nirsevimab.^[8]
• Adults aged 18 years and older, including immunocompromised adults.^[2][7]
• Children aged 5 to 18 years with chronic medical or immunocompromising conditions.^[6]
• People with inflammatory rheumatic diseases such as rheumatoid arthritis.^[3]
• Allogeneic haematopoietic stem cell transplant recipients and lung transplant recipients.^[1][5]

What are the trials measuring?

The trials measure several different outcomes. The infant trials count symptomatic RSV respiratory tract infections confirmed by a positive RSV test by 12 months of age.^[8][4] The DAN-RSV trial measures hospitalisation for RSV-related respiratory tract disease.^[2] The transplant trials measure seroconversion — whether antibody levels rise by a defined amount after vaccination.^[1][5] The rheumatic disease trial measures the fold-change in RSVpreF-specific IgG antibody from before to after vaccination.^[3] The children's trial measures safety, tolerability, and neutralising antibody titres against RSV A and B.^[6] A non-interventional study is also evaluating the real-world effectiveness of Abrysvo in infants born to vaccinated pregnant women.^[9]