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Respiratory Syncytial Virus Vaccine, Adjuvanted (Arexvy)

By William Elliott, MD, FACP, and James Chan, PharmD, PhD

Dr. Elliott is Assistant Clinical Professor of Medicine, University of California, San Francisco.
Dr. Chan is Associate Clinical Professor, School of Pharmacy, University of California, San Francisco.

The FDA has approved the first respiratory syncytial virus (RSV) vaccine for older adults.1 Patients older than age 65 years living with chronic lung or heart disease and weakened immune systems are at highest risk for developing severe RSV infections.2 The vaccine received priority review, fast-track, and breakthrough therapy designations. It is distributed as Arexvy.


Arexvy can be administered to prevent lower respiratory tract disease (LRTD) caused by RSV in patients age 60 years and older.3


Inject one 0.5-mL dose intramuscularly.3 Arexvy is a recombinant RSV glycoprotein F stabilized in prefusion conformation (RSVPreF3) as the antigen component. The solution also includes AS01 adjuvant lipid A from Salmonella minnesota and saponin from plant extract Quillaja saponaria Molina combined in a liposomal formulation.3


This is the first vaccine approved for RSV after it showed an overall efficacy rate of 82.6% in reducing the risk of RSV-associated LRTD.1,3


The most common solicited adverse reactions (vs. placebo) were local injection site pain (61% vs. 9.3%), fatigue (34% vs. 16%), myalgia (29% vs. 8%), headache (27% vs. 13%), and arthralgia (18% vs. 6%).3 In one study, two participants who received the RSV vaccine along with an influenza vaccine developed acute disseminated encephalomyelitis, a rare type of brain and spinal cord inflammation.1 One of those subjects died.


Arexvy is a subunit vaccine comprised of the RSVPreF3 antigen genetically engineered using Chinese hamster ovary cells. The efficacy of the vaccine was based on an ongoing Phase III, randomized, placebo-controlled, observer-blinded study conducted in 17 countries.3 Subjects age 60 years and older were randomized to a single dose of the RSV vaccine (n = 12,466) or placebo (n = 12,494). Vaccine efficacy was based on prevention of a first episode of confirmed RSV-A- and/or B-associated LRTD during the first season. Researchers confirmed cases by quantitative reverse transcription polymerase chain reaction on nasopharyngeal swab during acute respiratory illness. LRTD was defined as the participant experiencing at least two LR symptoms/signs, one for at least 24 hours, or at least three LR symptoms for at least 24 hours. The median follow-up time for the primary efficacy analysis was 6.7 months.

Overall vaccine efficacy was 82.6% (95% CI, 57.9-94.1). The risk of severe RSV-associated LRTD was lowered by 94%. There was no evidence suggesting interference of immune response with concomitant administration of RSV vaccine and quadrivalent flu vaccine (Fluarix Quadrivalent) one month apart.3


RSV infection leads to approximately 60,000 to 120,000 hospitalizations and 6,000 to 10,000 deaths in the United States annually.1 Arexvy is shown to be effective in lowering the risk of RSV-associated-LRTD, and other vaccines are under investigation. The results from an interim analysis of Pfizer’s bivalent (RSV subgroups A and B) RSVPreF nonadjuvanted vaccine for older adults (n = 34,284) suggested the solution could lower the risk of RSV-associated LRTD with at least two or three signs or symptoms by 66.7% (95% CI, 37.1-77.9).4 Pfizer also evaluated their bivalent RSVPreF in pregnant women to prevent medically attended RSV illness in infants.5 Vaccine efficacy for severe illness within 90 days after birth was 81.8% (99.5% CI, 40.6-96). However, efficacy was 57.1% (99.5% CI, 14.7-79.8) for LRTD and did not meet the statistical success criteria of > 20% for the lower boundary.

On May 18, an advisory committee recommended FDA approval of Pfizer’s vaccine, with some committee members voicing concerns about risk of preterm birth.6 A final decision from the FDA on both Pfizer vaccine indications is expected this year.


1. U.S. Food & Drug Administration. FDA approves first respiratory syncytial virus (RSV) vaccine. May 3, 2023.

2. Centers for Disease Control & Prevention. Respiratory syncytial virus infection (RSV). Page last reviewed April 26, 2023.

3. GSK plc. Arexvy prescribing information. May 2023.

4. Walsh EE, Pérez Marc G, 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.

5. Kampmann B, Madhi SA, Munjal I, et al. Bivalent prefusion F vaccine in pregnancy to prevent RSV illness in infants. N Engl J Med 2023;388:1451-1464.

6. Hensley S, Stein R. FDA advisers support approval of RSV vaccine to protect infants. National Public Radio. May 18, 2023.