Sanofi and GlaxoSmithKline (GSK) are set to begin a new Phase II study of their COVID-19, after a delay to the programme was announced in December 2020.

The delay to the programme was announced after Phase I/II study results found a low immune response in older adults who received Sanofi/GSK’s investigational adjuvanted, recombinant protein-based COVID-19 vaccine.

The jab did induce an immune response comparable to recovered COVID-19 patients in adults aged 18-49 years, however the disappointing results in older adults caused Sanofi/GSK to postpone further testing of the vaccine.

At the time, the companies said that the low immune responses observed in older adults was likely caused by an ‘insufficient concentration of antigen’.

The new Phase II study will involve 720 volunteers aged 18 years and over, and will include equal numbers of adults aged 18 to 59 years and those 60 years and above.

The study will test three different antigen doses with a fixed dose of adjuvant in the total study population, at sites in the US, Honduras and Panama.

Sanofi/GSK said in a statement that results of the Phase II trial will inform the Phase III protocol, adding that if data from the new trial is positive, a global late-stage trial could begin in the second quarter of 2021.

Depending on the outcome of the potential Phase III trial, regulatory submissions for the vaccine could be expected in the second half of 2021, with the vaccine likely to then be available in Q4 2021 if approved.

“We are pleased to be starting this new Phase II study. The world needs multiple vaccines and we are confident that combining our proven pandemic adjuvant system with this improved antigen formulation will have significant potential as the pandemic evolves,” said Roger Connor, president of GSK Vaccines.

“We look forward to further progressing this vaccine candidate to Phase III in Q2 2021, if this Phase II study is successful,” he added.