Phase 3 Trial Confirms Immune Response and Safety Profile of Arexvy in Older Adults

A study published in the Journal of Infectious Diseases confirms the immune response and safety profile of a single dose of Arexvy, an AS01E-adjuvanted respiratory syncytial virus prefusion F protein vaccine, also known as RSVPreF3 OA, in adults aged 60 and older.

Respiratory syncytial virus (RSV) is a common virus that spreads easily and causes respiratory illness. Most people who get RSV have mild, cold-like symptoms. However, RSV can sometimes cause more serious lung problems like bronchitis and pneumonia, which might lead to hospitalization in some cases. Older adults, especially those with weakened immune systems or chronic heart and lung diseases, are at higher risk for severe illness from RSV.

Up to 160,000 older adults are hospitalized each year due to RSV and up to 10,000 die, according to the Centers for Disease Control and Prevention (CDC). Immunizations are available to help protect against severe RSV illness for at-risk individuals. Currently, three RSV vaccine products are licensed by the Food and Drug Administration: GSK’s Arexvy, Pfizer’s Abrysvo, and Moderna’s mResvia. Although two of the three shots have been available since last year, less than 25% of older Americans (ages 60 and greater) have been vaccinated, as of May 2024.

The Arexvy vaccine targets both RSV-A and RSV-B, two antigenically distinct groups of the virus, and has shown high efficacy in prior studies.

This phase 3 trial, which involved 1,653 participants across multiple countries including the United States, Germany, and Japan, aimed to assess the immune response and safety profile of the newly approved vaccine.

Interim results from this trial indicate that one month following vaccination, neutralization titers — a key measure of the vaccine's effectiveness — rose significantly, showing a 10.5-fold increase for RSV-A and a 7.8-fold increase for RSV-B compared to pre-vaccination levels. Although these titers declined over the following months, they remained elevated, at 4.4-fold (RSV-A) and 3.5-fold (RSV-B) above baseline at six months, and 3.1-fold (RSV-A) and 2.3-fold (RSV-B) after one year.

The vaccine was well-tolerated among participants, with the majority reporting mild to moderate side effects. The most common side effects were pain at the injection site, muscle pain, tiredness, and headache. Serious adverse events were reported by 3.9% of participants. Only one of these events, a case of Guillain-Barré syndrome that eventually resolved, was related to the vaccine.

This study highlights the significant impact of the Arexvy vaccine in fostering robust immune responses. The ongoing trial aims to monitor these responses for up to three years post-vaccination to determine how long protection lasts and inform future vaccination strategies to protect older adults from the potentially severe consequences of RSV infection.