Sanofi and GSK have commenced a global phase 3 clinical study to evaluate the safety, efficacy, and immunogenicity of their adjuvanted recombinant-protein Covid-19 vaccine.

The phase 3 study is designed to enrol more than 35,000 volunteers, aged 18 years and above, at sites in different countries including the US, Asia, Africa, and Latin America.

Prevention of symptomatic Covid-19 in SARS-CoV-2 naïve adults is the primary endpoint of the study, and prevention of severe Covid-19 disease and prevention of asymptomatic infection are the secondary endpoints.

The companies are jointly developing the Covid-19 vaccine, where Sanofi contributes its recombinant antigen and GSK its pandemic adjuvant, both vaccine platforms with established activity against influenza.

Sanofi Pasteur executive vice president and global head Thomas Triomphe said: “We are encouraged to see first vaccinations starting to take place in such an important, pivotal Phase 3 study, as we believe that our unique technology platform will provide a clinically-relevant vaccine option.

“We have adapted our vaccine development strategy based on forward-looking considerations as the virus continues to evolve, as well as anticipating what may be needed in a post-pandemic setting.

“This trial is testament to the urgency and agility in our approach to help overcome the ongoing impact of this pandemic.”

Adjuvanted recombinant Covid-19 vaccine produced 95 to 100% seroconversion rates

The phase 3 study is planned to be conducted in a two-stage approach, where it will initially evaluate the vaccine formulation targeting the original D.614 virus (Wuhan), while a second stage will evaluate a formulation targeting the B.1.351 (South African) variant.

It is based the positive results from a phase 2 study, in which adjuvanted recombinant Covid-19 vaccine produced high immune responses, with 95 to 100% seroconversion rates.

According to recent scientific evidence, antibodies created against the B.1.351 variant may provide broad cross-protection against other more transmissible variants.

Furthermore, conducting the phase 3 trial across diverse geographies is expected to facilitate the evaluation of the vaccine candidate against a variety of circulating variants.

The companies expect to get approval for the vaccine in the fourth quarter of this year, subject to positive phase 3 outcomes and regulatory reviews.

GSK vaccines president Roger Connor said: “We believe further solutions for COVID-19 are very much needed to help reach people around the world, especially as the pandemic evolves and variants continue to emerge.

“Adjusting our technology and study designs reflects this need and will further build the potential of this adjuvanted protein-based vaccine.

“We are grateful to the volunteers who will take part in the trials and hope the results will add to the encouraging data we’ve seen so far so we can make the vaccine available as quickly as possible.”