Pfizer has reported positive top-line results from its Phase III MONeT study (NCT05842967) evaluating the efficacy of single-dose Abrysvo for adults at risk of developing severe respiratory syncytial virus (RSV)-associated lower respiratory tract disease (LRTD).

As per the 9 April press release, Abrysvo met its co-primary immunogenicity and safety endpoints, with patients demonstrating non-inferior RSV-A and RSV-B neutralising responses compared to the Phase III RENOIR study (NCT05842967) where the vaccine previously showed efficacy.

Compared to pre-vaccination, the vaccinated patients also demonstrated a minimum of a four-fold increase in serum-neutralising titers for RSV-A and RSV-B a month after being vaccinated. The MONeT trial did not identify any new safety signals for Abrysvo.

The pharma giant plans to publish the findings in a peer-reviewed journal and submit the results to regulatory agencies in a bid to expand the vaccine’s label from its current indication to include adults 18 years and older, the announcement stated.

The randomised, parallel-assignment MONeT study comprises two substudies that assessed the safety, tolerability, and immunogenicity of Abrysvo in adults at risk of RSV-associated disease.

Substudy A was a double-blinded study administering 120µg single-dose Abrysvo or placebo to patients with certain chronic medical conditions that were not immunocompromising in a 2:1 ratio. Substudy B was a single-arm, open-label, trial that evaluated the two 120µg doses of the vaccine with an interval of one month in immunocompromised adults.

Abrysvo, a subunit vaccine containing a recombinant RSV F protein antigen, is designed to stimulate an immune response against RSV prefusion conformation (pre-F) that protects the body against lower respiratory tract disease caused by RSV. The vaccine, which first gained US Food and Drug Administration (FDA) approval in May 2023 for the prevention of LRTD caused by RSV in adults aged 60 years or older, was approved in August 2023 for use in pregnant women to offer protection for their babies.

The race for RSV vaccine approval finally ended in May 2023 when the FDA approved Arexvy as the first vaccine for the prevention of LTRD caused by RSV in adults aged 60 years and older.