Sanofi and GSK COVID-19 vaccine candidate demonstrates strong immune responses in Phase 2 trial


  • Adjuvanted recombinant COVID-19 vaccine candidate triggered strong neutralizing antibody responses in all adult age groups

  • High immune response after a single dose in patients with prior infection shows strong booster potential

  • Global Phase 3 study expected to start in the coming weeks


PARIS and LONDON – May 17, 2021 – The Sanofi and GSK adjuvanted recombinant COVID-19 vaccine candidate achieved strong rates of neutralizing antibody responses, in line with those measured in people who have recovered from COVID-19, in all adult age groups in a Phase 2 study with 722 volunteers. A global pivotal Phase 3 study is expected to start in the coming weeks.


The Phase 2 interim results showed 95% to 100% seroconversion following a second injection in all age groups (18 to 95 years old) and across all doses, with acceptable tolerability and with no safety concerns. Overall, the vaccine candidate elicited strong neutralizing antibody levels that were comparable to those generated by natural infection, with higher levels observed in younger adults (18 to 59 years old). After a single injection, high neutralizing antibody levels were generated in participants with evidence of prior SARS-CoV-2 infection, suggesting strong potential for development as a booster vaccine.


“Our Phase 2 data confirm 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. “With these favorable results, we are set to progress to a global Phase 3 efficacy study. We look forward to generating additional data and working with our partners around the world to make our vaccine available as quickly as possible.”


Roger Connor, President of GSK Vaccines added: “These positive data show the potential of this protein-based adjuvanted vaccine candidate in the broader context of the pandemic, including the need to address variants and to provide for booster doses. We believe that this vaccine candidate can make a significant contribution to the ongoing fight against COVID-19 and will move to Phase 3 as soon as possible to meet our goal of making it available before the end of the year.”


Based on these positive Phase 2 interim results, the companies plan to initiate a global Phase 3, randomized, double-blind study with the 10µg dose, in combination with GSK’s pandemic adjuvant, in the coming weeks. This Phase 3 trial is expected to enroll more than 35,000 adult participants from a broad range of countries and will assess the efficacy of two vaccine formulations including the D614 (Wuhan) and B.1.351 (South African) variants.


In parallel, the companies intend to conduct booster studies with various variant formulations in order to assess the ability of a lower dose of the vaccine to generate a strong booster response regardless of the initial vaccine platform received.

Pending positive Phase 3 outcomes and regulatory reviews, the vaccine is expected to be approved in the fourth quarter of 2021.



Original news