Pfizer has commenced the Phase III RENOIR clinical trial of a single-dose respiratory syncytial virus (RSV) bivalent prefusion F subunit experimental vaccine candidate, RSVpreF, in adults aged 60 years or above.

First participants in the trial have been inoculated, the company said.

RSVpreF builds on certain discoveries, including those at the US National Institutes of Health (NIH), which described the crystal structure of a key type of viral protein that RSV leverages to attack human cells.

The international, randomised, double-blind, placebo-controlled Phase III trial will assess the efficacy, immunogenicity and safety of the vaccine in nearly 30,000 subjects.

The safety and efficacy of the vaccine in preventing moderate to severe lower respiratory tract illness (msLRTI-RSV) during the first RSV season will be the trial’s primary goals.

Pfizer Vaccine Research & Development senior vice-president and head Kathrin Jansen said: “There is an important unmet medical need for an effective vaccine that can help protect older adults against this highly contagious disease.

“The start of this Phase III study is an important step forward towards our goal of comprehensive immunisation against RSV disease, which includes developing a potential first vaccine to help prevent RSV disease in adults, as well as the ongoing efforts to help protect infants through maternal immunisation, subject to regulatory approval of the candidate vaccine.”

A common and prevalent cause of acute respiratory illness, RSV is highly contagious and impacts the lungs and airways.

The US Food and Drug Administration granted fast track status to RSVpreF in November 2018 to prevent lower respiratory tract illness caused by RSV in infants by actively immunising pregnant women.

The company reported positive top-line data from Phase IIb proof-of-concept study of the vaccine in April 2020.

This trial assessed the safety, tolerability and immunogenicity of the shot in vaccinated pregnant women aged 18 to 49 years and their infants.

In July 2021, Pfizer offered an update on a Phase IIa trial of RSVpreF in a virus challenge model in healthy adults aged 18 to 50 years.

The data from the Phase IIa trial analysing the safety, immunogenicity and efficacy of the vaccine facilitated the company to progress to Phase III trial.

The latest development comes after Pfizer dosed the first subject in Phase II/III clinical trial of its experimental oral antiviral drug, PF-07321332, for Covid-19 in non-hospitalised patients who have symptoms but are at low risk of progression to severe disease.