On May 17, 2021, Sanofi and GSK reported that their 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.

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. The Phase 3 trial is expected to enrol 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.

The Phase 2 study interim results show that the adjuvanted recombinant vaccine candidate triggered a strong immune response amongst adults of all age groups with 95% to 100% seroconversion rates and neutralizing antibodies that were comparable to those generated by natural infection. The high titers observed in the non-naïve population after one dose of the vaccine candidate also suggest it may have strong potential for use as a booster vaccine. Full results of the Phase 2 study will be published in a peer-reviewed journal.

The randomized, double-blind, multi-center dose-ranging study was conducted in healthy adults aged 18 years of age and older, including those with high risk medical conditions, to evaluate the safety, reactogenicity, and immunogenicity of two injections given 21 days apart, with 3 antigen dose levels of 5, 10 and 15 µg. Beginning in February 2021, the study enrolled 722 volunteers, in the U.S. and Honduras. It included equivalent numbers of adults 18 to 59 years and those 60 years and above. Pending positive Phase 3 outcomes and regulatory reviews, the vaccine is expected to be approved in the fourth quarter of 2021.