Moderna has dosed the first subject in the Phase II/III trial of its respiratory syncytial virus (RSV) vaccine candidate, mRNA-1345.

The investigational single-dose mRNA vaccine candidate encodes for a prefusion F glycoprotein, eliciting a superior neutralising antibody response.

It contains optimised protein and codon sequences, as well as uses lipid nanoparticle (LNP) similar to the company’s Covid-19 vaccine.

Named ConquerRSV, the randomised, multicentre, placebo-controlled, observer-blind Phase II/III trial will be conducted in many countries.

Moderna is selecting locations of the trial depending on the ongoing RSV epidemiology and is expected to enrol nearly 34,000 subjects.

The Phase II part’s primary goal is to assess the safety of the RSV vaccine candidate in adults aged above 60 years to begin the Phase III segment.

Meanwhile, the primary purpose of the trial’s Phase III portion is to evaluate the efficacy and safety of mRNA-1345 in participants of the same age group to support licensure.

Moderna CEO Stéphane Bancel said: “We believe that the vaccine candidate against RSV can have a positive impact on public health as RSV represents a significant unmet global need.

“In addition, we believe that combination vaccines against multiple respiratory pathogens can help ensure that people are fully vaccinated by leading to higher compliance and better uptake, which may result in a longer-term benefit to healthcare systems and protect people from a broader number of respiratory viruses.”

The company recently shared interim data from a Phase I trial of the vaccine conducted in adults aged between 65 and 79 years.

It demonstrated that a single mRNA-1345 dose of 50µg, 100µg or 200µg increased neutralising antibody titers against RSV-A and RSV-B by nearly 14-fold and ten-fold, respectively.

Moderna also noted that throughout month one, a single mRNA-1345 vaccination dose of 50µg, 100µg or 200µg was found to be well-tolerated in older adults.

Furthermore, mRNA-1345 received Fast Track designation from the US Food and Drug Administration (FDA) this August for RSV in adults aged above 60 years.