Sanofi and GlaxoSmithKline (GSK) have announced the initiation of a new Phase II study of their adjuvanted recombinant protein COVID-19 vaccine candidate.

The Phase II trial is a randomised, double-blind, multi-centre dose finding study and will evaluate the safety, reactogenicity and immunogenicity of two injections of the vaccine given 21 days apart in 720 volunteers aged 18 and over. It will assess three different antigen doses with a fixed dose of adjuvant in order to select the most appropriate antigen dosage for Phase III evaluation.

Importantly, said the companies, the trial will include equal numbers of adults 18 to 59 years and those 60 years and above. This is to ensure that the selected dose works well for all ages, as Phase I/II data published in December 2020 indicated adults aged 50 years and over had a lower immune response to the vaccine than those aged 18 to 49 years. The enterprises stated this was likely due to an insufficient concentration of the antigen.

“Over the past few weeks, our teams have worked to refine the antigen formulation of our recombinant-protein vaccine, based on learnings from our initial Phase I/II study,” said Thomas Triomphe, Executive Vice President and Head of Sanofi Pasteur. “We are confident that our vaccine candidate has strong potential and we are very encouraged by the latest preclinical data. This new Phase II study will enable us to identify the final vaccine formulation for adults of all ages. We have demonstrated our commitment to focusing efforts and capabilities towards the global fight against the pandemic, and this new study takes us a step closer to achieving our primary goal of developing a COVID-19 vaccine with a good efficacy and safety profile.”

The companies added that, if data from the new Phase II trial are positive, a global Phase III study is planned to start in the second quarter of 2021. Positive results from the Phase III study would lead to regulatory submissions in the second half of 2021, with the vaccine expected to be available in quarter four of 2021, if approved.

In parallel to the new trial, Sanofi has commenced the development work for vaccines that could tackle emerging strains of SARS-CoV-2 that may impact on vaccine efficacy. This research will be used to inform the next stages of the Sanofi/GSK development programme.