Sanofi and GlaxoSmithKline (GSK) have reported that their COVID-19 vaccine generates strong immune responses across all adult age groups.

In February, the companies announced that they would begin the new Phase II study of their COVID-19 vaccine following a delay to the programme in December 2020.

The delay to the programme came 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’.

In the new Phase II study, Sanofi/GSK’s jab achieved strong rates of neutralising antibody responses, similar to those measured in people who have recovered COVID-19, in all adult age groups.

The results showed also showed 95% to 100% seroconversion following second injections in all age groups – 18 to 95 years old – and across all doses tested.

Sanofi/GSK added that high neutralising antibody levels were generated in participants with evidence of prior SARS-CoV-2 infection after a single injection, suggesting a ‘strong’ potential for its development as a booster jab.

Following the positive results, the companies are planning to initiate a global Phase III trial ‘in the coming weeks’.

This pivotal trial will aim to enrol over 35,000 adult participants from a range of countries, and will assess the efficacy of two vaccine formulations including the Wuhan (D614) and South African (B.1.351) variants.

“Our Phase II data confirm[s] the potential of this vaccine to play a role in addressing this ongoing global public health crisis, as we know multiple vaccines will be needed, especially as variants continue to emerge and the need for effective and booster vaccines, which can be stored at normal temperatures, increases”, said Thomas Triomphe, executive vice president and global head of Sanofi Pasteur.